CARROT

Daucus carota var. sativus

Leaf Blight (fungus - Alternaria dauci): Infection occurs mostly on older leaves but young plants may also be attacked. Leaf blight first appears as indefinite brown to black areas with pale yellow centers. Infected leaves shrivel when infection is heavy. Under these conditions foliage appears as if burned by fire. The fungus overwinters in infected crop refuse. Air-borne spores of the fungus are produced in large numbers on old lesions during periods of high humidity. Spores may also be carried on seed. The fungus requires moisture for infection. A preventative fungicide program should be followed where the disease is a threat. Spray interval should be every 10 to 14 days depending on fungicide used.

Leaf Spot (fungus - Cercospora carotae): This disease may occur at any place on the leaf but is most common on margins. Spots are circular in shape and with age they coalesce to form larger spots. Lesions on the leaves are sometimes surrounded by a lighter circle or halo. Lesions on the petioles are enlongated with a pale center and dark margin. Spots on the petiole may encircle it causing defoliation. Leaf spot is distinguished from leaf blight by the nearly circular, sharply defined lesions with a yellow halo. The disease usually occurs during the latter part of the growing season and can be controlled with the same recommendations as for leaf blight.

Powdery Mildew (fungus - Erysiphe polygoni:) Although the fungus does not appear to cause excessive damage, it may cause serious infection under conditions favorable for disease development. Affected leaves are covered by a white, powdery mass of spores. Symptoms may also be found along petioles. Fungicide applications at 10 to 14 day intervals will control the disease.

Root Knot Nematode (nematode - Meloidogyne spp.): Root-knot nematodes seriously damage carrots and cause multiple tap-root formation. Root production is severely limited rendering the crop unmarketable. Nematodes contained in the roots are not harmful to humans when consumed. It is best to select areas free of root-knot nematodes for carrot production. Certain pre-plant nematicides can be used where the soil is infested.

Damping-Off (fungi- Rhizoctonia, Fusarium, etc.): Like many other vegetables, carrot seedlings are susceptible to attack by several kinds of soil- borne fungi, particularly during the periods of cool, humid weather. Infected seedlings wilt, turn brown and die, resulting in poor stands. Plant on a bed, do not overwater, and control weeds as soon as possible after emergence.

Aster Yellows (Mycoplasma): The first symptom of aster yellows is yellowing of the foliage, followed by excessive growth and bunching of shoots. Older leaves become twisted and may fall off. Roots are misshapen, and of poor quality with many adventitious roots. The organism is introduced in the field by leafhoppers from overwintering infected weeds. The disease usually occurs sporadically with little economic loss.

See Cotton Root Rot:

CELERY

Apium graveolens var. dulce

Cercospora Blight (fungus - Cercospora apii): Symptoms begin as small, yellowish spots on both sides of the foliage. Spots enlarge quickly changing from yellow to ash-gray with the tissue drying in affected areas. The fungus also attacks leaf petioles and stems. Under conditions of high humidity and warm weather, a gray velvety growth can be seen on the surface of affected spots. The fungus is seed-borne and spores can also be blown in air currents for long distances. Warm temperatures are required for fungus development. Control is obtained by using disease-free seed treated with fungicides and spraying plants with a protective fungicide at regular intervals when disease represents a threat.

Late Blight (fungi - Septoria apiicola): Small, yellowish spots develop on the underside of the leaves which later spread to the entire foliage. Spots enlarge and turn brown, similar to lesions caused by Cercospora. Minute, black fruiting bodies can be found scattered in the affected areas. Lesions with fruiting structures can be seen on petioles and stems. High humidity, free water, and cool temperatures favor disease development. Fungicides recommended for Cercospora blight will also control late blight.

Stalk Rot (fungi - Rhizoctonia solani): A serious disease of celery that is favored by high temperatures and moist conditions. Symptoms are first seen as small lesions on the base of the petioles, near the ground. As the disease progresses, the spots are enlarged, appear watersoaked at first, turning later to a brick-red color. When matured, the spots are sunken and turn to a dark brown color that is characteristic of the disease. The lesion can be a few or numerous, making it necessary to trim a lot of the leaves, thus reducing quality and yield. Shallow planting on raised beds and fungicide applications serve to reduce disease losses.

See Root Knot Nematode (nematode - Meloidogyne spp.):

Zea mays var. saccharata

Seed Rots and Seedling Disease (fungi - Pythium spp. Macrophomina phaseolina , Gibberella zeae, Penicillium oxalicum and others): Both seed rots and seedling disease can cause poor stands. Cool wet soils slow seed germination and development of young seedlings so that there is exposure to fungi for a longer period of time. Low quality seed also produce seedlings that are weak and survive poorly in cold wet soils.

Control is obtained by using high quality seed which have been treated with a protective fungicide. Sweet corn should be planted on raised bed after the soil temperature is above 55 degrees F.

Stalk Rot and Kernel Rot (fungus - Fusarium spp.): Infected plants are stunted and delayed in maturity. During periods of high wind plants often lodge. Ears may hang downward on the stalk. The Gibberella stage of the fungus will infect kernels causing them to be pink in color. Infected ears have a strong odor and should not be used as food or feed.

Control stalk rots by rotating with non-related crops, planting in well drained soils and by using treated seed.

Southern Corn Leaf Blight (fungus - Bipolaris maydis): The disease is easy to recognize under field conditions. Spots on the leaves are tan to brown in color. On the ear the fungus causes oblong, bleached spots which penetrate through the shuck layers and finally into the ear.

The fungus overwinters in crop residue and produces spores which can be carried for long distances by wind.

Northern Corn Leaf Blight (fungus - Exserohilum turcicum): This disease is found in most sweet corn fields, yet is seldom severe enough to cause economic loss. Spots produced are larger than those caused by the southern corn leafspot fungus. Spots are from one to six inches long and one-half to one inch wide. With maturity, the center of the spot has a dark brown color. Infection occurs first on older foliage. High humidity and temperatures between 60 to 80 degrees F favor disease development. Varieties vary in their reaction to the fungus.

Brown Leaf Spot (fungus - Physoderma maydis): The fungus causing this disease occurs in most fields but seldom does economic damage. Infection requires high temperatures and presence of surface moisture. The first symptom of the disease is small circular spots. As they mature they turn dark brown. Rotation and deep burial of stalks will help reduce losses to this fungus.

Downy Mildew (fungus - Peronosclerospora sorghi): Infected plants are chlorotic, stunted and have striped leaves. Infected leaves have a downy growth on the underside, toward the basal part. Potential infection is increased when the crop is grown in soil previously grown to infected sorghum, field corn or sweet corn. Although high populations of spores are produced on the leaf surface, they are short lived and require extended periods of high humidity for infection. Overwintering spores produced between leaf veins exist in the soil for long periods. Practices which hasten the breakdown of crop residue will help reduce the amount of inoculum carried over in the soil. Varieties vary in their reaction to this disease. Growers should consult their county Extension agent for current hybrids and their reaction to this disease.

Crazy Top Downy Mildew (fungus - Sclerophthora macrospora): This disease is a problem when fields become flooded early in the life of the plant. The fungus produces swimming spores which require water for mobility.

Infected plants are sterile and have numerous shoots at the base of the stalk. Leaves are thickened, distorted, of a lighter green color than normal leaves. Tassels and ears develop green leafy shoots.

The fungus is commonly found in grasses along the edge of the field. Spores are washed into the field in flood water. Infection of the young corn plants takes place at this time.

Varieties vary in their reaction to this fungus. Due to the low percentage of occurrence, little has been done to rate varieties for their reaction. Avoid fields that flood regularly and plant on a raised bed which will help reduce the exposure of young seedlings to standing or flowing water.

Common Rust (fungus - Puccinia sorghi): Common rust occurs in most home gardens and commercial fields, but seldom causes economic losses. Infected leaves have raised spots or pustules formed primarily on the upper surface. The pustules are rectangular, brick red and occur in bands on the leaf. Spores are produced in the pustules, which are blown to neighboring leaves where infection can be repeated. Infection is encouraged by high humidity and cool temperatures (60 to 70 degrees F).

Common Smut (fungus - Ustilago maydis): Common smut is often found in fields of sweet corn. Losses from common smut vary based on the amount of infected plants in the field. Galls are formed as the common smut fungus causes cells of the corn plant to increase in size and number. These galls at first are covered with a thin white membrane. As the gall ages, the membranes break open to reveal a black powdery spore mass underneath. The spores are blown to adjoining corn plants where infection is repeated. Common smut of sweet corn is more of a problem during dry weather, which slows down the growth of the corn plant. Plants grown in soils high in nitrogen or plants damaged through cultivation are most susceptible to infection.

To control common smut, use resistant hybrids and plant high quality seed. Sweet corn should be grown on soil that is fertilized according to a current soil test recommendation.

Corn Stunt (spiroplasma): Corn stunt occurs in a small percentage in most sweet corn fields. It seldom reaches levels high enough to cause economic loss. The corn stunt spiroplasma is transmitted by leafhoppers. Infected plants are stunted, young leaves are yellow in color, and with age they take on a reddish-purple color. Internodes are reduced in length and infected stalks are sterile. Control is not required due to the very low percentage of plants that normally show this symptom in the field.

Maize Dwarf Mosaic (virus): Maize Dwarf Mosaic virus is the most common virus disease of sweet corn in Texas. Infected plants have mottled upper leaves that are lighter in color than healthy leaves. The mottled or mosaic pattern consists of alternate yellow and green islands in the leaf tissue. Aphids transmit virus particles from surrounding Johnsongrass. Johnsongrass rhizomes serve as the overwintering host for this virus. Early infected plants may be sterile. Late infection will reduce yields and quality of corn produced. Insect control is not successful due to the feeding pattern of the aphid. Elimination of Johnsongrass and isolation of sweet corn fields from Johnsongrass stands will help reduce the occurrence of this disease. There are a number of hybrids of sweet corn that are resistant.

See Charcoal Rot

Plant Parasitic Nematodes: (See Root Knot and other nematode sections.)

EGGPLANT

Solanum melongena

Leaf Spot and Fruit Rot (fungus - Phomopsis vexans): This disease is characterized by circular brownish spots on fruit and leaves. On the fruit, soft, sunken spots become rotted and shrivelled. Spray with approved fungicide beginning when fruit is first set and repeat at 10-day to two week intervals until fruit is nearly mature. Use a three year crop rotation. Florida High Bush, Florida market and Florida Beauty are resistant. Early Blight (fungus - Alternaria solani): This disease can be destructive on eggplant at any time in the life of the plant. It can cause seedling dieback known as collar rot. Later infection is on the foliage beginning on the lower part of the plant and developing upward. Spots are characterized by concentric rings which give a target appearance. Plants which are well fertilized and irrigated are not as susceptible. Infection of the fruit pedicels may cause a premature fruit drop. It requires eight to 10 days after infection before visible symptoms develop to the extent that epidemic levels are reached. Injured fruit are more subject to attack by the fungus than healthy fruit. Infection occurs between 60 and 90 degrees F. Long rotations, weed control, adequate fertilizer, and irrigation (furrow) will help reduce losses. Use clean seed and follow a thorough spray program when this disease is a problem.

Colletotrichum Fruit Rot (fungus - Colletotrichum melongenae): Lesions on the fruit vary from small spots to one-half inch in diameter. The tissue is sunken, with an area filled with a flesh-colored ooze of fungal spores. Spots vary from one to several on the fruit surface. Severely infected fruit drop to the ground with the pedicel still attached to the plant. The fungus overwinters in plant residue and grows at temperatures of 55 to 95 degrees F with optimum growth at 80 degrees F. Rainfall and overhead irrigation favor disease development. The fungus develops when the humidity is 93 percent or above. Although field sanitation is important, a preventive fungicide spray program is required during periods favorable for disease development.

Wilt (fungus - Verticillium albo-atrum): The pathogen attacks nearly 200 species of plants but eggplant and okra are the two most seriously affected vegetables. Young plants appear normal, but become stunted as they develop. Severely affected plants turn yellow. The lower foliage wilts and defoliation occurs. Symptoms continue to progress until death occurs. When the stem is cut, there is a dark brown, discolored band around the vascular system. Infection occurs directly through the root hairs. The fungus survives for indefinite periods in the soil. Survival is aided by weeds which are susceptible to the fungus. Infection takes place when the temperature ranges from 55 to 86 degrees F. Verticillium is favored in its development if the soil is alkaline. Some development takes place at pH of 5.0 but all growth is stopped at a pH of 4.0. Control involves the use of long rotations. Cotton gin trash should be avoided or be well composted if used.

Yellows (Tobacco Ring Spot Virus): The disease causes yellowing and whitening of upper leaves. Later, entire plant becomes yellow and may die. Avoid planting in fields where yellows have occurred and, if warranted, fumigate soil to control nematodes. The dagger nematode is a known vector of the virus.

ENGLISH PEA

Pisum sativum

Powdery Mildew (fungus - Erysiphe polygoni): Plants infected with this fungus are covered with a white powdery mold on the leaves, stems and pods. Infected plants are stunted and eventually die. The fungus is seed-borne. Optimum temperatures for development are between 68 and 75 degrees F. Soils should be kept as dry as possible yet will permit maximum growth. Avoid heavy application of fertilizer and rotate with non-related crops. Powdery mildew is the most serious disease of English peas in Texas.

Bacterial Blight (bacterium - Pseudomonas syringae pv. pisi): The bac- terium attacks all parts of the plant. Infected stems become olive brown in color, while the leaflets become yellowish or water-soaked. Young infected pods drop prematurely. Well formed pods become water-soaked.

The bacterium is seed-borne. Rain or irrigation water is necessary for movement of the organism. After infection takes place, four to six days is required before lesions are visible. Optimum temperature for development is 82 degrees F.

Control of this pathogen is through a combination of practices such as drainage, row spacing, seeding rates, weed control, and restricting irrigation only to that needed for maximum plant growth.

Ascochyta Blight (fungi - Ascochyta pisi, A. pinodella, A. pinodes): All three fungi are known to attack peas. Affected leaves have spots which are large, pale brown to dark brown in color. Lesions are papery in appearance and have gray to tan centers marked by small black pycnidia. Infection by some species cause purple lesions. On pods, deep lesions are formed which may have purple margins. The center is tan with black pycnidia.

Planting infected seed results in poor stands. All three species of fungi are seedborne and carry over in crop residue. Rainfall and heavy dews are necessary for infection. No infection occurs when the relative humidity is below 80 percent. Optimum temperatures for the fungus are between 68 and 82 degrees F.

Control is achieved by using clean seed, long rotations (four years or longer), planting in well-drained soil, and deep plowing to remove old crop residue.

Aphanomyces Root-Rot (fungus - Aphanomyces euteiches): Early infection causes complete crop loss due to seedling death. Late infection results in poor plant growth and reduced seed formation. Tissue decay does not develop above the soil line unless the weather is extremely wet. Infection occurs in both wet and dry soils, but is most destructive in wet soils. Optimum temperatures for infection are between 65 and 75 degrees F. The use of high levels of fertilizer will encourage continued root development. Nitrogen acts as a suppressant to fungal growth.

The use of three year rotation, well-drained soil, and the liberal use of fertilizer will help reduce losses from this disease. Mosaic (virus): Irregular, light and dark, greenish areas and puckering occurs in leaves. Control aphids that transmit the virus.

Chlorosis: (See section on Chlorosis.)

See Charcoal Rot

See Root Knot Nematode

Introduction

These Disease Management Guidelines were put together for growers with an interest in the "Organic" production of apples in Ohio. In current organic production systems, growers are not permitted to use conventional synthetic organic fungicides in their disease management program. If fungicides are required in the organic system, growers are limited to the use of "Inorganic" fungicides such as sulfur (elemental sulfur and lime-sulfur) or copper (Bordeaux mixture and basic copper sulfate). There are several problems associated with the use of these inorganic fungicides in modern apple production systems. Among the most important are: 1) phytoxicity, which is the potential to cause damage to foliage, fruit set and fruit finish, and 2) their limited spectrum of activities, which means they may not be capable of providing simultaneous control of the wide range of fungal pathogens that can cause economic damage to the crop.

In a climate like Ohio, environmental conditions during the growing season are generally very conducive to the development of several important diseases, insect pests and weeds. Limitations in relation to which pesticides may or may not be used, present the organic grower with some unique and very demanding challenges.

This Disease Management Program should aid organic growers in achieving an acceptable level of disease control. However, the successful control of diseases alone is generally not sufficient to provide a commercially acceptable level of fruit quality in the Midwest and northeastern United States. Unless similar programs are developed and implemented for controlling insects, weeds and other pests (i.e., deer), I strongly question if the organic production of apples on a commercial scale is feasible in Ohio.

Pest management will remain one of the major challenges and constraints facing the organic production of fruit and vegetables in Ohio. In my opinion, growers need to be fully aware of the unique challenges involved, before making any substantial economic commitments.

Objective of the "Organic" disease management program.

The overall objective of this disease management program is to provide a commercially acceptable level of disease control, with minimal pesticide use. This is accomplished by developing a disease management program that integrates the use of disease resistance, various cultural practices, and knowledge of disease biology to minimize fungicide use. When fungicides are used within the disease management program, they must be acceptable within organic certification programs.

For information on organic production and standards or requirements for organic certification, contact the following organizations: Ohio Ecological Food and Farm Association, 65 Plymouth Street, Plymouth, OH 44865; Phone: 419-687-7665; and Organic Crop Improvement Association, 3185 Township Rd. 179, Bellefontaine, OH 43311

A. DISEASES THAT NEED TO BE CONSIDERED WITHIN THE DISEASE MANAGEMENT PROGRAM.

I. Early Season Diseases:

Apple Scab	Powdery Mildew	Cedar Apple Rust

Unless disease resistant varieties are used, all of these diseases must be controlled with the use of fungicide early in the growing season (from green tip or 1/2 inch green through first to third cover, mid to late June). Failure to control scab and powdery mildew during this period will result in secondary infections occurring throughout the remainder of the growing season. Late season (secondary) infection of scab and mildew will result in increased fungicide usage late in the growing season in order to achieve acceptable control.

II. Late season or "Summer Diseases"

Secondary scab - if primary scab is not controlled.	Black Rot	Sooty Blotch
Secondary mildew - if primary mildew is not controlled.	White Rot	Fly Speck

We need to emphasize early season control of primary scab and powdery mildew so that late season (after mid to late June) fungicide applications for these diseases will not be required. If primary scab and mildew are controlled, then black rot, white rot, sooty blotch and fly speck are the major diseases we need to consider in the late season (end of June through harvest) fungicide program.

III. Other Diseases

Fire blight

Collar Rot

Each of these diseases may require specific control measures and each will be discussed separately.

B. IDENTIFYING AND UNDERSTANDING THE MAJOR APPLE DISEASES.

It is important for growers to be able to recognize the major apple diseases. Proper disease identification is critical to making the correct disease management decisions. In addition, growers should develop a basic understanding of pathogen biology and disease cycles. The more you know about the disease, the better equipped you will be to make sound and effective management decisions.

C. UNDERSTANDING THE EARLY SEASON DISEASES (SCAB, MILDEW AND RUSTS)

1. APPLE SCAB BIOLOGY - The importance of early season disease control.

Much of the fungicide spray program for apples in Ohio is directed at the control of apple scab. Therefore, growers that have scab susceptible varieties need to develop a thorough understanding of the apple scab disease cycle before a successful disease management program can be developed.

Note: If scab resistant varieties are used, apple scab requires no other control measures.

a) Primary Disease Cycle

The fungus overwinters in diseased apple leaves on the orchard floor. In late fall and early spring, microscopic, black, pimple-like structures, called pseudothecia, are produced in these dead leaves. Within each pseudothecium are sac-like structures called asci, each with eight ascospores. The ascospores produce the first, or primary, infections on the new growth in the spring.

Apple Scab Disease Cycle

Pseudothecial development in the old dead leaves is favored by alternating periods of wetness and dryness in late winter and early spring. Normally, pseudothecia have mature ascospores when the blossom buds start to open. When the leaves on the orchard floor become wet, ascospores are forcibly ejected into the air. Air currents carry them to the emerging tissues where infection takes place. Maturation and discharge of ascospores usually lasts one to several weeks past petal fall. After this time, there are no ascospores left to cause primary infections.

Environmental conditions that affect ascospore discharge.

Ascospore discharge is induced after dead leaves on the ground have been wetted by at least .01 inches of rain for a least 1/2 hour. After 2 to 3 hours of wetness, the maximum rate of discharge will be reached. After about 6 hours of wetness, 75% of the ascospores that are mature during that wetness period will have been discharged. Some recent research indicates that most ascospore discharge occurs only during daylight.

Ascospore germination begins as soon as a spore lands on young, green leaves or fruit, provided a film of moisture is present. After primary infections occur, lesions are produced in about 1-2 weeks on leaves and fruit. Each lesion (which was caused by a single ascospore) will produce hundreds of thousands of conidia, each of which is capable of causing a new infection. Secondary infections caused by conidia can result in economically damaging levels of fruit scab. The number of hours of wetting required for infection by ascospores varies with temperature. Information on the environmental conditions (leaf wetness duration and temperature) required for scab infection is provided in Table 1.

It is important that growers understand the basic disease cycle for apple scab in order to develop the most successful disease management program.

THE BOTTOM LINE FOR APPLE SCAB CONTROL

In order to effectively control apple scab, you must control primary infections from ascospores. If ascospores are prevented from infecting leaves and fruit early in the season, no further scab control measures are needed after the supply of ascospores is depleted. However, if early-season infections are not controlled, additional fungicide protection is required throughout summer to protect against secondary infections by conidia. The number of conidia produced by just a few early-season scab lesions is much greater than the total number of ascospores produced in an entire acre of leaf litter in most clean, commercial orchards.

Note: Organic growers should use scab resistant varieties whenever possible. If scab resistant varieties are used, no fungicides for scab control are necessary.

b) Secondary Disease Cycle:

Secondary infections are initiated by conidia produced in primary lesions. Since conidia may develop as soon as 7 to 9 days after infection, secondary infections may be initiated very early in the growing season (prebloom). This is particularly true when ascospores infect the apical portions of sepals and leaves near bud break. Conidia are disseminated by splashing rain and by wind. Conidial germination and infection occurs under about the same conditions as for ascospores.

Although developing fruit become more resistant as they mature, secondary infection to fruit can occur before harvest in the fall but not show up until the fruit have been stored for several months. The disease also can build up on the leaves after harvest. Since the fungus overwinters in these leaves, pseudothecia may be present in sufficient quantity to start the new season even though a good spray program was followed the previous year.

The Bottom Line For Secondary Scab Control is to use a good early season program to eliminate primary infections. Once infections are established in the orchard, the use of additional fungicide sprays throughout the growing season to control secondary scab will probably be required.

Note: If scab resistant varieties are used, no other control measure is required. The use of disease resistance must be emphasized within the Organic program.

Get more apple scab info - facts and photos here

II. POWDERY MILDEW BIOLOGY

Powdery mildew (PM) is generally not as severe a problem as scab in most Ohio orchards. However, under certain environmental conditions and on highly susceptible varieties, powdery mildew can become a major problem.

The conditions required for infection by the PM fungus are very different from those required by the scab fungus. It is important that growers understand these basic differences in order to develop a disease management program for managing both diseases simultaneously.

a) Powdery Mildew Disease Cycle

Dormant period

Powdery mildew overwinters as fungal strands (mycelium) in vegetative or fruit buds which were infected the previous season. Infected terminals may have a silvery gray color, stunted growth, and a misshapen appearance, and are more susceptible to winter kill than are healthy terminals. Temperatures near -18 F kill a majority of mildew infected buds and the fungus within them. Unfortunately, even at lower temperatures some PM survives.

The PM fungus produces masses of small black structures called cleistothecia on infected leaves and terminals in the late summer and fall. Although the cleistothecia contain ascospores, their role in the disease cycle is not clearly understood.

Primary Infection

As buds break dormancy, the powdery mildew fungus resumes growth and colonizes developing shoots causing primary infections (Figure 2). The powdery white appearance on infected shoots consists of many thousands of spores which are responsible for spreading the fungus and causing secondary infections. Primary mildew infections may occur on vegetative shoots and blossoms and thereby cause a reduction in yield.

Secondary Infection

Secondary infections are important because they result in the overwintering infected buds and fruit infections. Secondary infections usually develop on leaves and buds prior to terminal bud set in mid-summer and may reduce the vigor of the tree. Young fruit may become infected from about the pink stage of flower development through 1 to 3 week after bloom. Fruit infection results in a weblike russetting on the mature fruit.

b) Environmental Conditions That Favor Infection.

Powdery mildew infections occur when the relative humidity is greater than 90% and the temperature is between 50-77 F. The optimum temperature range for the fungus is 66-72 F. Although high relative humidity is required for infection, the spores will not germinate if immersed in water. The high relative humidity that often occurs before and after wetting periods (rainfall or dew) is conducive to powdery mildew development; however, unlike the apple scab fungus, the powdery mildew fungus does not require leaf wetness for infection. Under optimum conditions, powdery mildew will be obvious to the unaided eye 48 hr after infection. About 5 days after infection, a new crop of spores is produced. Non-germinated powdery mildew spores can tolerate hot dry conditions and may persist in the orchard until favorable conditions for germination and infection occur.

Note: As a general "rule of thumb" disease pressure from powdery mildew is greater in growing seasons following mild (warm) winters. The critical period for powdery mildew control is from about "tight cluster to pink" through "first" or "second" cover.

Note: Several scab resistant varieties also have good resistance to powdery mildew. The use of disease resistance must be emphasized within the Organic Program.

Get more powdery mildew info - facts and photos here

III. RUST DISEASES

Rust diseases and causal fungi include: 1) cedar apple rust, caused by Gymnosporangium juniperi-virginianae; 2) quince rust, caused by G. clavipes; and 3) hawthorn rust, caused by G. globosum. All three fungi spend part of their life cycle on red cedar and are problems only when red cedar is found close to the orchard. The life cycles and control of these diseases are similar.

Cedar-apple rust is the most important rust disease in Ohio and the disease is generally more severe in the southern portion of the state. In Ohio, the rust diseases are generally not a serious problem to apple production; however, if the disease is established on cedar (juniper) within a 2-mile radius of the orchard, serious losses can result.

a) Cedar-Apple Rust Disease Cycle

The disease cycle is very similar for all three rusts and is very complex. For the purposes of this discussion, cedar-apple rust will be used as an example. Two plants (apple and cedar) and three fungal fruiting structures (telia, aecia and pycnia) are involved. The pathogen requires 2 yr. to complete its life cycle.

The cedar-apple rust and hawthorn rust fungi overwinters in reddish-brown galls or "cedar apples" in the cedar tree. The quince rust fungus overwinters in elongated galls in cedar branches. When galls become wet during spring rains, they extrude gelatinous tendrils or "horns" consisting of microscopic two-celled teliospores, each of which produces four basidiospores. Air currents carry the basidiospores to the apple leaf and fruit where they infect under favorable conditions. Leaves are most susceptible when they are 4 to 8 days old. Apple leaves and fruit can only be infected by the basidiospores of the rust fungus from cedar trees. Thus, when the basidiospores have all been discharged from the spore hornes on cedar trees, the danger from infection on apple is past. There is no secondary cycle or infections on apple. Once the lesions form on leaves or fruit, they will not spread or cause additional infections on apple. Instead, another type of spore (aeciospore) is produced and during July and August, these aeciospores are carried by wind back to the cedar trees where they cause infection and complete the life cycle of the fungus.

Note: The basidiospores that infect apple are produced and released from galls on cedar trees from about the "Pink" stage of apple bud development, until about "First" to "Second" cover. If fungicide is required to control this disease, this period is most critical for timing sprays.

Note: Apple varieties differ greatly in their susceptibility to rusts. Many scab resistant cultivars also have good resistance to cedar-apple rust, which is the most common rust disease in Ohio. It is important to realize that the resistance reported to rust in the disease resistant apple varieties is for cedar-apple rust. The varieties may not be resistant to quince rust. Due to the lack of effective fungicides for rust control, if quince rust is a serious problem in the area, organic production may not be feasible unless you can eliminate cedar trees within at least a 1/2 mile radius. The use of disease resistance must be emphasized in the Organic disease control program.

b) Bottom Line For Rust Control.

Use rust resistant varieties and eradicate the alternate host within at least a 1/2 mile radius of the orchard.

Get more cedar-apple rust info - facts and photos here

Get quince rust info - facts and photos here

D. UNDERSTANDING THE LATE SEASON OR "SUMMER" DISEASES (SOOTY BLOTCH, FLY SPECK, BLACK ROT, WHITE ROT)

I. SECONDARY SCAB - This should not be a problem if primary scab in controlled or scab resistant varieties are used. See previous section on apple scab biology.

II. SECONDARY MILDEW - This should not be a problem if powdery mildew is controlled early in the season or mildew resistant varieties are used. See previous section on powdery mildew.

III. SOOTY BLOTCH AND FLY SPECK - These two diseases are caused by different fungi, but the environmental conditions that favor their development and the management strategies for this control are very similar. Sooty blotch and fly speck are common names of two diseases often found on apple and pear fruit at the same time. Sooty blotch is caused by Gloeodes pomigena and fly speck by Microthyriella rubi. They do little or no actual damage to the fruit, but their presence on the fruit's surface lowers quality and the subsequent market value. The diseases occur throughout the eastern apple-growing areas of the United States, but are most severe in the southern fruit-growing regions. Both fungi also occur on the bark, stems and leaves of many other plant species with waxy cuticles.

a) Disease Cycle

Both pathogens overwinter on twigs of many woody plants. Gloeodes pomigena is spread from these overwintering hosts by waterborne conidia or mycelial fragments. Spread of M. rubi is by airborne ascospores, which are discharged during rain periods or by airborne or waterborne conidia. Fruit infection can occur anytime after petal fall but is most prevalent in mid- to late-summer. Both diseases are favored by moderate temperatures, high humidity and abundant rainfall. The diseases are most severe in orchards where fog or heavy dews are common through the mid-to-late growing season. Gloeodes pomigena and M. rubi are primarily restricted to the fruit's cuticle. Fruit severely affected with sooty blotch may shrivel more readily in storage.

b) Environmental Conditions That Favor Disease Development.

Both diseases are favored by temperatures between 65⁰ and 80⁰F and by high humidity (greater than 90% relative humidity for sooty blotch and greater than 95% relative humidity for fly speck). Conditions such as these occur frequently when nighttime temperatures remain above 65⁰ to 70⁰F during summer, or during extended warm rainy periods. Sooty blotch and fly speck symptoms can develop within 14 days from infection under ideal conditions, but symptom development is arrested by high temperatures and low relative humidity. Thus, the period between infection and symptom development ranges from 25 to more than 60 days in the Northeast. Sooty blotch and fly speck infections not yet visible at harvest can develop during cold storage.

Note: All varieties, including scab resistant varieties are susceptible to sooty blotch and fly speck.

BOTTOM LINE FOR SOOTY BLOTCH AND FLY SPECK CONTROL

i) Emphasis must be placed on cultural practices that increase air circulation and reduce drying time of fruits and foliage.

CULTURAL PRACTICES THAT AID IN CONTROL OF SOOTY BLOTCH AND FLY SPECK

Any management practice which improves air movement and reduces relative humidity within the orchard and tree canopy will aid in reducing the incidence of sooty blotch and fly speck. Management strategies that encourage good air movement and speed drying include dormant and summer pruning, keeping orchards well mowed, and removing hedgerows or adjacent woodlots that obstruct air flow. Removing hedgerows will also remove some of the inoculum sources.

Pruning is the most important cultural practice for improving air movement and reducing drying time in the tree canopy. The combination of good dormant and summer pruning will aid greatly in controlling sooty blotch and fly speck.

Dr. Dan Cooley (University of Massachusetts) reported that summer pruning alone resulted in a 50% decrease in the incidence of flyspeck in an orchard that received no summer fungicides. Summer pruning and traditional dormant pruning also opens tree canopies so that in addition to providing increased air movement, better spray coverage of fruits during late summer is also accomplished.

Adequate fruit thinning is also important for minimizing the incidence of Sooty Blotch and Fly Speck. If fruit are clustered (more than two fruit per spur), it becomes virtually impossible to maintain adequate fungicide coverage in the center of the clusters as fruit mature. Clustered fruit often have flyspeck on their inner faces even where an adequate fungicide program has been used.

Growers wishing to minimize the need for summer fungicides in new orchards should recognize that site selection and tree spacing will ultimately impact on incidence of summer diseases in these orchards. High density orchards may provide a faster return on investment, but tight spacings will also result in dense canopies and poor air movement between trees as the plantings mature.

ii) If fungicide is required, sulfur or Bordeaux mixture are the only choices. During wet growing seasons or on problem sites, fungicide application may be required. Sulfur is at best only "fair" for controlling these diseases. Bordeaux mixture is much more effective than sulfur and will provide longer residual activity. See "Comments" on copper in the suggested spray schedule.

iii) Chlorine Dip for Removing sooty Blotch and Fly Speck.

Research at the University of Georgia by Dr. Floyd Hendrix Jr. has shown that a 5-7 minute dip in 500 ppm chlorine in the dump tank of a commercial packing line, followed by brushing and a fresh water rinse was effective in removing both diseases from apple fruits. For severely infected fruit, the longer time period may be required. Dr. Hendrix saw no phytotoxicity on red delicious fruit soaked for 15 min in a 4100 ppm chlorine solution (personal communication). Pennwalts liquid Sodium Hypochlorite is labeled for use in this post harvest dip.

Note: Before using any chemical in the organic program, first check to see if it is acceptable for use in organic production.

Get more sooty blotch and fly speck info - facts and photos here

IV. SUMMER ROTS - Black Rot, Bitter Rot and White Rot

There are three summer fruit rots that can occur in Ohio: black rot, bitter rot and white rot. Of these diseases, black rot, and white rot can be commercially important problems. The rather intensive fungicide program that is generally maintained to control our other major diseases probably adds greatly to the control of the summer rots. Where conventional fungicides such as captan are used, summer rots seldom occur as a significant problem. As we develop new programs and strategies that reduce our overall fungicide use, these rots may become more important.

Note: There is good potential for these diseases to become serious problems in organic production systems. Sulfur is not effective in controlling any of the summer rots. In organic systems any cultural practice (primarily sanitation) that aids in controlling these diseases must be emphasized.

Black Rot

Black rot of apple fruit is caused by the fungus Botryosphaeria obtusa. It also causes frog-eye leaf spot. In addition, the fungus causes a limb canker. The limb canker phase is most important in the northeastern and north central apple growing regions of the United States, and leaf spot and fruit rot phase is most important in the southeast.

a) Disease Cycle

Botryosphaeria obtusa overwinters in dead bark, twigs, cankers and mummified fruit. Ascospores and conidia are released during rainfall throughout the growing season and are washed or blown onto fruit and foliage. Ascospores are generally more common during the spring than summer months. Sepal infection can occur any time during the growing season. Leaf infection is most common just after petal fall. Black rot infection of leaves and fruit commonly develops in cone-shaped areas on the tree beneath black rot mummies or old fire blight cankers. Early-season infection may result in fruit drop. Severely diseased fruit may mummify and remain attached to the tree.

b) Environmental Conditions That Favor Disease Development

The optimum temperature for leaf infection (frog-eye leaf spot) is 80⁰F; at this temperature, 4.5 hours of wetting is required for light infection. No infection occurs at 46⁰F, even with 48 hours of wetting. The optimum temperature for fruit infection ranges from 68⁰F to 75⁰F, and 9 hours of wetting is required for fruit infection to occur.

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White Rot

White rot is also referred to as Botryosphaeria rot or Bot rot. The disease is most severe in trees weakened by drought, winter injury, sunscald, poor pruning, low or unbalanced nutrition, and other plant diseases. White rot can be sporadic in appearance, being serious one season and difficult to find in the following season. The Botryosphaeria fungus attacks a wide range of woody plants that are common in Ohio.

Dutchess, Golden Delicious, Grimes Golden, Gallio Beauty, Rome, and Yellow Transparent apple varieties are all very susceptible to white rot. Jonathan and Red Delicious are less affected than other varieties. In addition to fruit rot, the disease can also result in cankers on twigs and limbs.

a) Disease cycle

The fungus overwinters as black pycnidia and perithecia in a wart-like stroma on living and dead cankered limbs and in rotted or mummified fruits. The fungus is also commonly found on fire-blighted twigs or cankers. Wounds or breaks in the epidermis are necessary for the fungus to penetrate. Spores (ascospores) are forcibly discharged from the perithecia during spring rains. Another type of spore (conidia) is produced within pycnidia and ooze out in tremendous numbers. They are then washed and rain-splashed to other parts of the plant throughout the summer. Apple fruits may become infected fairly early in the season, but the rotting does not develop much until the fruit is almost mature. At temperatures above 75⁰F (24⁰C), mature fruit may rot completely within a few days after infection. The development of Botryosphaeria canker and fruit rot is favored by any condition that reduces tree vigor.

b) Environmental Conditions that Favor Disease Development

The optimum temperature for germination of ascospores and conidia is 82 to 90⁰F. Germination can occur in as little as 90 min at 82⁰F. Germination is greatest in free water, but some can occur in the absence of free water at relative humidity as low as 96%. Wounding is not necessary for fruit infection, but entry through wounds is probably the most important means of infection. Infection of wounded fruit can occur in as little as 2 hours at 82⁰F.

Get more white rot info - facts and photos here

C. CULTURAL PRACTICES THAT AID IN BLACK ROT AND WHITE ROT CONTROL

a) Maintain trees in a healthy vigorous condition. Prune trees annually and maintain good soil fertility based on foliar and soil analysis.

b) Sanitation is probably the most important cultural practice that aids in control of these diseases. Piles of prunings are an important source of inoculum and should be removed from the perimeter of the orchard or burned. Prunings can be left on the orchard floor if they are chopped with a flail mower, which removes much of the bark. All dead, cankered, or infected twigs and limbs should be carefully pruned, then removed from the orchard and destroyed (preferably by burning) during the winter. This will reduce the carryover of the fungi. Old, weak, and diseased trees should be destroyed.

Removal of mummified apples in the tree is important for reducing the inoculum within the tree. Pruning out current-season shoots infected with fire blight is also important, because they can be colonized and serve as an inoculum source during the same growing season.

c) Handle fruit very carefully while picking, sorting, and packing to avoid bruises and cuts which are quickly colonized by the fungi.

d) Refrigerate fruit promptly after harvest. Although rot can develop in cold storage, disease development is greatly reduced at temperatures below 40⁰F.

E. DISEASE MANAGEMENT OPTIONS FOR ORGANIC PRODUCTION SYSTEMS.

I. Options:

Option 1) Do not use Fungicides

Use Disease Resistant Apple Cultivars and Emphasize the Use of Good Cultural Practices. The use of scab resistant or "immune" varieties will greatly reduce the need for early season fungicide use. In fact, by using a variety such as "Liberty" that has resistance to scab, mildew and rust, the need for early season fungicide application is essentially eliminated. Several new varieties have multiple resistance to the early season diseases. These varieties are not resistant to the summer diseases. However, the diligent use of good cultural practices that have been described will greatly aid in controlling these diseases. If the use of disease resistant varieties combined with good cultural practices does not provide an acceptable level of disease control, the use of fungicide will be required.

Note On The Use of Fungicides in Organic Production Systems: The use of disease susceptible varieties that require the intensive use of fungicides to control diseases is strongly discouraged within an Organic Production System. In fact, this approach is probably doomed to failure in the long run. The use of disease resistant varieties and rootstocks that require no or minimal fungicide use must be emphasized in organic systems.

Option 2) Use Inorganic Fungicides (copper and sulfur) In a Protectant Fungicide Program.

This program requires a 4-7 day interval between fungicide sprays from green tip to 1/2 inch green through first or second cover (through primary scab) for control of the early season diseases on susceptible varieties, then a 10-14 day interval between the remaining cover sprays through harvest for control of summer diseases. During wet growing seasons, the shorter interval will probably need to be used, and during dry growing seasons the interval can usually be extended.

If used in conjunction with good cultural practices, this program should provide acceptable disease control, but it requires an intensive use of fungicides. The only fungicides currently acceptable for use within organic programs in Ohio are elemental sulfur, lime sulfur, Bordeaux mixtures (copper plus lime), and basic copper sulfate. Although these are actually "inorganic" compounds (contain no carbon atoms) they are often referred to as "organic" fungicides. The following is intended to provide some general information about these fungicides.

a) Copper Fungicides

In general, copper fungicides are very effective against most apple diseases and provide good residual activity, thus increasing the time interval required between sprays. However, copper fungicides have some very important disadvantages that growers need to understand before they use them.

When different formulations of copper are dissolved in water, copper ions are released into solution. These copper ions are toxic to fungi and bacteria because of their ability to destroy proteins in plant tissues. However, because copper can kill all types of plant tissues, the use of copper fungicides carries the risk of injuring foliage and fruit of most crops. Factors promoting this injury include: 1) the amount of actual copper applied, and 2) cold, wet weather (slow drying conditions) that apparently increases the availability of copper ions and, thus, increases the risk of plant injury. Because of the potential to injure plants, the use of copper fungicides for fruit disease control has largely been replaced with the synthetic, organic fungicides that are safer to plant tissues and often more effective. The use of copper fungicides on apple after the 1/2 inch green stage of bud development through about 4 to 5 weeks past bloom will probably result in some level of fruit russet.

Several terms are used when discussing copper as a fungicide. The original material used was copper sulfate (also known as blue vitriol or bluestone). When this material was combined with lime in French vineyards, the combination became known as Bordeaux mixture.

Bordeaux Mixture

Bordeaux mixture is a mixture of copper sulfate and hydrated lime in water. The formulation of Bordeaux mixture is usually expressed by using three numbers, such as 8-8-100 or 6-8-100. The first number is the amount of copper sulfate in pounds; the second is the amount of hydrated (spray) lime in pounds and the last number is the gallons of water they are mixed in. For example, an 8-8-100 Bordeaux mixture is 8 lbs. of copper sulfate plus 8 lbs. of spray lime in 100 gallons of water. The addition of lime to copper sulfate makes it safer for use on plants. The lime reacts with the copper ions making them more stable. Thus, copper compounds in the presence of lime will generally produce lower, more uniform concentrations of free copper ions, which in turn is less likely to injure plant tissues. Bordeaux mixture has long residual activity and has been used to control fire blight and apple scab. The use of copper (Bordeaux Mixture) in the later cover sprays (mid-to late-summer) may result in acceptable fruit finish and good disease control; however, I feel that the use of copper on apple anytime after bud break is risky and may result in damage to fruit and foliage. Bordeaux mixture is available as a wettable powder or it can be made on the farm (see below). Bordeaux mixture is approved for use in organic production in Ohio.

Fixed Copper Fungicides

Following the discovery and use of Bordeaux mixture, several relatively insoluble copper compounds or fixed coppers were developed. Fixed copper formulations may be less injurious to plant tissues than Bordeaux mixture, but their use is still limited because of their potential to injure plants and lack of compatibility with other pesticides. Some of the more common formulations of fixed copper include C-O-C-S, Kocide 101, Tribasic Copper Sulfate, and Tenn-Copp 5E. There are many copper fungicide formulations on the market.

Note: Before using any form of fixed copper fungicide, check to make sure it is approved for use in organic production in Ohio (see note page 4). It must be emphasized that these copper containing compounds are fungicides and must be labeled for use on apple before they can be used. Label instructions must always be followed.

b) Sulfur Fungicides

Sulfur is available as liquid lime sulfur, dry wettable powders, and in liquid or flowable formulations. The following are some of the more common and readily available types.

Liquid Lime-Sulfur or Lime-Sulfur Solution is a 29% solution of calcium polysulfide. It is rather caustic material and smells like rotten eggs but it is a good fungicide and is accepted within many organic certification programs. The labels I have seen do not mention its use on apple past petal-fall or first cover. In addition, if it is used past tight cluster it may result in poor fruit finish (russet).

Dry Wettable Sulfurs

Dry wettable sulfurs are available under many trade names. The microfine wettable sulfurs are usually much less injurious to foliage and fruit than liquid lime sulfur, but their use during hot weather (above 80 F) may result in some leaf burning and fruit russeting.

Flowable Sulfurs

Flowable sulfurs are also available from several manufactures. The most common formulation I have seen is the 6F which contains 6 pounds of sulfur per gallon. Due to smaller particle size, flowable sulfurs may be a bit more efficacious than wettable powders. Flowable sulfurs are often preferred to wettable powders because they do not create dusts that can be inhaled during loading and measuring operations.

Various other forms of sulfur such as dispensable granules are also available.

Note: Elemental sulfur and lime sulfur are approved for use in organic production systems in Ohio.

General Comments on Sulfur

Sulfur is highly effective for control of powdery mildew. It is "at best" only fair for control of apple scab and summer diseases and provides no control of rusts. A major problem with the use of sulfur as a fungicide is the lack of residual protectant activity. Sulfur only provides about 3-5 days of protection. When sulfurs were the only fungicides being used in the past, up to 25 applications per season were necessary to obtain satisfactory control.

Growers should also note that sulfur is toxic to many beneficial insects, spiders and mites. These beneficial insects are natural predators of harmful insects and mites that affect fruit crops. Killing these beneficial insects may increase certain insect problems, especially with mites.

II. A Suggested Fungicide Spray Schedule for Organic Production Systems In Ohio (Option 2).

Important Note:

The following spray schedule is only intended to provide guidelines for organic growers that need to use fungicide in order to obtain satisfactory disease control. Organic growers must understand that it may not be feasible to use "organic" fungicides on a strict calendar schedule with a precise number of days between sprays. Calendar spray schedules are feasible with some of the conventional synthetic, organic fungicides such as captan because they provide enough residual activity to allow a specific number of days between sprays. Sulfur, on the other hand, only provides 3-5 days of protective activity and needs to be applied just prior to rains that are infection periods (Table 1). Thus, the timing of fungicide sprays within an "organic" spray schedule will be largely dictated by weather conditions.

Growers should pay close attention to the "Comments" sections within this spray schedule.

Timing	Disease Controlled	Fungicide and (Rate/100 gal)
Green tip to 1/2 inch green	Scab	Copper fungicide (see label) or Lime-Sulfur (1.5-2 gal) or Microfine Wettable Sulfur (6 lb.) or Flowable Sulfur 6F (5 qt.)

Comments

If scab was a problem in the orchard last year, copper or lime-sulfur should be the fungicide of choice. Lime-sulfur is incompatible with oil and should not be applied within 3 weeks of an oil spray. The use of a copper fungicide past 1/2 inch green is not recommended due to fruit finish problems (russet) and potential damage to foliage and overall tree health.

If sulfur is used, it should be re-applied after every rain, and may need to be re-applied after each additional 1 inch of rain during long wetting periods until the danger of primary scab infection is past.

Timing	Disease Controlled	Fungicide and (Rate/100 gal)
Tight Cluster (5-7 days after 1/2 inch green	Scab Powdery Mildew	Lime-Sulfur (1.5-2 gal) or Microfine Wettable Sulfur (6 lb.) or Flowable Sulfur 6F (5 qt.)

Comments

The use of lime-sulfur past tight cluster may result in fruit finish problems and damage to leaves; however, if scab is established in the orchard or disease pressure is severe, lime-sulfur would be the fungicide of choice.

The labels I have seen for lime-sulfur recommend its use up to petal-fall or first cover, depending upon the manufacturer.

If sulfur is used, it should be re-applied after every rain, and may need to re-applied after each additional 1 inch of rain during long wetting periods until the danger of primary scab infection is past.

Timing	Disease Controlled	Fungicide and (Rate/100 gal)
Open Cluster to Pink (5-7 days after tight cluster)	Scab Powdery Mildew Rust	Lime-Sulfur (1.5-2 gal) or Microfine Wettable Sulfur (6 lb.) or Flowable Sulfur 6F (5 qt.)

Comments

This is an important period for disease control. See comments on lime-sulfur and sulfur above, under tight cluster.

Timing	Disease Controlled	Fungicide and (Rate/100 gal)
Bloom (5-7 days after previous spray)	Scab Powdery Mildew Rust	Microfine Wettable Sulfur (6 lb.) or Flowable Sulfur 6F (5 qt.)

Comments

See comments on lime-sulfur under tight cluster. Sulfur sprays will probably need to maintained on a 5-7 day schedule.

Timing	Disease Controlled	Fungicide and (Rate/100 gal)
Petal Fall (When last petals are falling or 5 -7 days after previous spray)	Scab Powdery Mildew Rusts Sooty Blotch Fly Speck Black Rot White Rot	Microfine Wettable Sulfur (6 lb.) or Flowable Sulfur 6F (5 qt.)

Comments

Fruit Finish: The time from bloom to about second cover (4 to 5 weeks past bloom) is thought to be the most critical time for fruit russet due to pesticides. Sulfur is probably the safest material available. Unfortunately, it is also the least effective. Sulfur applications need to be maintained on a 5-7 day schedule until the danger of primary scab infection is over. (See page 6, Environmental conditions that favor ascospore discharge.)

Lime-Sulfur: The labels I have seen for lime-sulfur solution state that applications can be made up to petal fall or first cover, depending upon the manufacturer. My interpretation of the label is that lime-sulfur is not labeled for use in the cover sprays. Thus, other labeled formulations of sulfur must be used to control summer diseases in the cover sprays past petal fall.

Copper: I have not found a label for a copper fungicide (other than Bordeaux Mixture, Tri-basic copper sulfate, and Tenn-Cop 5E) that is registered for use on apple past petal-fall. The Bordeaux Mixture I have seen is sold in small packages primarily intended for homeowner use. I feel that the use of copper during the period from 1/2 inch green through 4 to 5 weeks past bloom will probably result in serious fruit finish (russet) problems. However, copper fungicides should provide good control of the summer diseases in the later cover sprays when temperatures are higher and if they are not applied under slow drying conditions. If growers decide to use Bordeaux Mixture for summer disease control, they should consider avoiding its use from bloom through second or third cover which is considered to be the critical period for russet. Remember that there is always some risk of fruit and foliar damage anytime copper is used during the growing season. Check labels of products to verify their registrations for use on fruit after petal-fall.

Timing	Disease Controlled	Fungicide and (Rate/100 gal)
First Cover (5 -7 days after Petal Fall)	Scab Powdery Mildew Rusts Sooty Blotch Fly Speck Black Rot White Rot	Microfine Wettable Sulfur (6 lb.) or Flowable Sulfur 6F (2.5 qt.)

Timing	Disease Controlled	Fungicide and (Rate/100 gal)
Second and Third Covers (10 - 14 days after First Cover)	Scab Powdery Mildew Rusts Sooty Blotch Fly Speck Black Rot White Rot	Microfine Wettable Sulfur (6 lb.) or Flowable Sulfur 6F (2.5 qt.)

Comments

Sulfur is not very effective in controlling the summer diseases. The use of good cultural practices must be emphasized if sulfur is expected to provide acceptable control. During wet growing seasons a shorter interval between sprays may needed.

Timing	Disease Controlled	Fungicide and (Rate/100 gal)
Remaining Covers (10 - 14-day intervals through harvest)	Sooty Blotch Fly Speck Black Rot White Rot	Microfine Wettable Sulfur (6 lb.) or Flowable Sulfur 6F (2.5 qt.) or Bordeaux mixture (see label)

Comments:

If summer diseases are a persistent problem in the orchard, growers may want to consider the use of Bordeaux mixture in the later cover sprays (after third cover). Although the risk of damage to fruit finish and foliage still exists, it is minimized during these later sprays. Copper should not be applied during cool temperatures or under wet, slow drying conditions. The 14 day interval should be satisfactory for copper fungicides and during dry growing seasons the interval could probably be extended to 21 days.

Do not apply sulfur if the temperature is warmer than 80⁰F. If summer diseases are a problem, the spray interval for sulfur should not exceed 10-14 days. Regardless of the fungicide being used, the use of good cultural practices to aid in summer disease control must be emphasized.

F. APPROACHES TOWARD REDUCING THE USE OF FUNGICIDES FOR SCAB CONTROL.

1) Use scab resistant cultivars. This eliminates the need for fungicides to control scab.

2) Reduce scab inoculum levels in the orchard.

a. After leaves drop in the fall, pulverize them with a mower. This will speed up their decay. Obviously, if leaves do not overwinter in the orchard, they can't serve as a source of primary inoculum in the spring.

b. Apply nitrogen to leaves on the ground or in the tree just before they drop to speed up their degradation. Some tests in North Carolina have used 5 lbs. of urea per 100 gal of water (personal communication: Dr. Turner Sutton). In theory this sounds good, and some discussion about this approach surfaces from time to time; however, I would not recommend this approach until more research has been conducted and specific recommendations are available.

3) Good pruning practices (both summer and dormant pruning) to open up the tree canopy will be beneficial in increasing the efficacy of the fungicide spray program. Open canopies result in better air circulation and light penetration that aid in reducing the length of wetness periods, in addition to providing for better spray penetration and coverage.

4) Properly calibrate the sprayer and make sure that you are getting complete coverage of all susceptible plant parts.

G. OTHER IMPORTANT DISEASES THAT NEED TO BE CONSIDERED.

a) Collar Rot (Crown Rot) of Apple

Collar rot, caused by the soil borne fungus Phytophthora cactorum is a chronic problem in midwestern apple orchards, several other Phytophthora species can also cause collar rot on apple. Collar rot is especially severe on trees that are grown on Malling Merton 106 (MM.106) rootstocks. The disease is most frequently associated with those areas of the orchard having heavy, poorly-drained soil. Phytophthora collar rot attacks the lower trunk just at or below the soil surface. One of the first indications of a collar rot problem is the production of smaller, chlorotic (yellowish) leaves in spring or early summer, and reddish or bronze colored leaves in late summer. This is soon followed by general stress symptoms which include poor terminal growth, small off-colored leaves, and numerous, small, brightly colored fruit. Cankers at the base of the main trunk can be recognized by the dark, sunken appearance of the bark. Tissue beneath the bark has a reddish to dark brown to black marbled appearance.

Collar Rot Control: Good water management and site selection are the most important factors for control of collar rot. Orchard soils should have good internal as well as surface drainage and should be leveled before planting. If collar rot occurs after trees are planted, improve drainage in the vicinity of the "saucer" around the base of the trunk. If subsurface drainage is a problem the only solution may be the installation of drainage tile through the area in which trees are planted, a task much more easily done before trees are planted! Select rootstocks that are not highly susceptible to collar rot. Although no rootstock is immune to collar rot, some are much more resistant than others.

Get more info on collar rot - facts and photos here

b) Fire Blight

Fire blight of apple and pear is a very serious disease on susceptible varieties. The disease is caused by the bacterium Erwinia amylavora. Incidence varies from year to year and severity is influenced by cultivar susceptibility, tree age, succulence of tissues and spring climatic conditions. The disease is most serious when temperatures during pre-bloom and bloom are warmer than average. Warm rainy periods at this time are particularly conducive to rapid spread of the pathogen resulting in blossom blight. Secondary blight of twig terminals occurs in late May through June during wind driven rains. Hail and wind damage provide openings that the pathogen enters. Insects with sucking mouth parts such as aphids and leaf hoppers may also be capable transmitting the disease to twig terminals. However, the role of insects in twig or shoot blight development is not clearly understood. Hot July weather generally slows disease progress. The bacterium overwinters in cankers on infected trees.

Fire Blight Disease Cycle

Fire Blight Control: Completely reliable control methods for blight are not available. Control strategies for this disease must include all aspects of fruit production. Resistant varieties of both apple, including scab-resistant varieties, and pear are available and should be planted wherever possible. Avoidance of blight susceptible rootstocks (M26, M9) especially when grafted to susceptible scions is encouraged. Cultural conditions should be modified if susceptible varieties are grown. Cultural practices which minimize rapid growth and succulent tissues should be practiced. Annual pruning with avoidance of major cuts will help minimize tree vigor. Similarly, limiting the amount of nitrogen fertilizer will reduce twig terminal growth. Fertilization should be based on the results of foliar and/or soil nutrient analysis. Other cultural practices which will help control fire blight include careful pruning of trees during dormancy to remove overwintering cankers.

Note: Certain years are "blight years" and even well-managed trees may be severely blighted. Organic growers should avoid varieties that are highly susceptible to fire blight.

Cutting Out Infected Twigs In The Growing Season

When large blocks of trees are severely affected by fire blight, it is difficult to determine whether removing fire blight strikes as they appear during summer is cost effective. In mature apple orchards that are not overly vigorous and do not include trees on M.9 or M.26 rootstocks, fire blight can often be left to run its course without endangering the tree. Older, nonvigorous trees will wall off the cankers before they spread very far in larger limbs. There is less risk of spreading the blight bacteria if pruning is delayed until winter, and winter pruning can be accomplished more efficiently because pruning tools need not be disinfected between cuts if pruning is done when trees are fully dormant. Generally, remove fire blight strikes during summer only if the following conditions exist:

1. The infections are in young, vigorous trees, where significant damage to the central leader and scaffold limbs will often occur if blight is not removed as it develops.

2. The infections are in dwarfing trees on highly sensitive rootstocks, such as M.9 or M.26, in which case the entire rootstock may die if exposed to inoculum from scion infections.

3. The number of infections in older trees is limited and can easily be removed.

4. Summer rot diseases such as black rot, bitter rot, or white rot have been a problem in the orchard. The removal of dead, blighted twigs is an important sanitation measure to prevent the increased development of these diseases.

Remove infected shoots during the growing season only on dry, sunny days. Make the cuts 8" to 10" below the visible canker. Disinfect the cutting tools between each cut, using 70% alcohol, 10% bleach, or 5% Lysol to avoid spreading the bacteria. When blight appears in an orchard, sucking insects should be controlled as long as the trees continue growing, to minimize secondary spread to new terminal shoots. Aphids and leafhoppers transmit fire blight, but their efficiency as disease vectors has not been determined. The usual control thresholds for aphids and leafhoppers are based on their feeding damage to trees and are not valid when they may be transmitting fire blight.

Get more info on fire blight - facts and photos here

Chemical Control of fire blight

Sprays of copper sulfate during dormancy and fixed copper or Bordeaux mixture (8-8-100) during early growth (no later than 1/2 inch green) may help reduce inoculum from cankers in the spring.

Recommended Spray Schedule For Fire Blight
DORMANT TO SILVER TIP
Before growth starts in the spring and when temperatures are above 45º F.

Pest/Problem	Material	Rate/100 gal	Low volume rate/acre	Comments
Fire blight	Bordeaux mixture OR Copper sulfate plus Superior oil (70 sec vis.)	8-8-100, plus oil (see comments) OR 5 lb. plus 1/2 gal.	not recommended not recommended	If fire blight was severe last year, a Bordeaux or copper spray at silver tip is suggested. Use a dilute Bordeaux spray of 8 pounds copper sulfate, 8 pounds spray lime, and 1 gallon miscible superior oil per 100 gallons of water. To mix, dissolve the copper sulfate in one-half tank of water. Once completely dissolved, add the spray lime with constant agitation as the tank fills. Add the oil last but before completely filling the tank. The mixture must be agitated continuously or the mixture will gel plugging nozzles, etc. Do not apply after 1/4 inch green leaf stage or when drying conditions are slow, as severe injury can occur. Bordeaux mixture and its residue have many compatibility problems with other pesticides. Do not apply copper sulfate plus oil past silver tip. It will burn any green tissue.

HALF INCH GREEN STAGE

Pest/Problem	Material	Rate/100 gal	Low volume rate/acre	Comments
Fire blight Scab	Bordeaux mixture	8-8-100, plus oil (see comments)	not recommended	See comments above. Do not apply copper during the period between 1/2 inch green and second or third cover or severe fruit finish problems may result. This spray may be beneficial for fire blight control and will also control apple scab. Some people have reported fruit finish problems, when copper fungicide was applied at 1/2inch green. The use of copper any time during the growing season is risky.

Note: Before using any copper compound, make sure that it is approved for use in Organic programs in Ohio or in other locations where fruit may be sold (see note page).

Some Links for Organic Insect and Disease Management:

• MSU Organic Apple Spray Program, by Mark Longstroth
• Organic Apple Production Guide for Nova Scotia, by G. Braun

Additional Resources:

The following literature contains color photographs of disease symptoms on apple, as well as information on pathogen biology and disease development.

"Compendium of Apple and Pear Diseases", is published by The American Phytopathological Society, 3340 Pilot Knob Rd., St. Paul, MN 55121, Phone: 612-459-7250. This is the most comprehensive book on apple diseases available. It has excellent color photos and all commercial apple growers should have a copy. Cost including shipping is $35.00 within the U.S.

"Management Guide For Low-Input Sustainable Apple Production", is a publication of the USDA Northeast LISA Apple Production Project. For detailed information about disease resistant cultivars, growers should obtain a copy of this publication from: Dr. David Rosenberger, Box 727, Highland, NY 12528. Make checks payable to: New York State Agricultural Experiment Station, Cost: $10.00 plus $2.00 shipping = $12.00.

"Diseases of Tree Fruits in the East", North Central Regional Publication No. 45, by Alan L. Jones and Turner B. Sutton. The publication has excellent color photos and is available for $10 from Michigan State University, Bulletin Office, 10-B Agriculture Hall, East Lansing, MI, 48824-1039, telephone (517) 355-0240 for more information.

Apple Disease Control

Guide H-317

Natalie P. Goldberg, Extension Plant Pathologist

College of Agriculture and Home Economics New Mexico State University

This publication is scheduled to be updated and reissued 4/05.

Several infectious disease agents (biotic pathogens such as fungi, bacteria, viruses, nematodes, and mycoplasmas) and non-infectious factors (abiotic factors such as temperature, moisture, nutrients, soil conditions, and chemicals) can cause diseases on apple trees. The climate in New Mexico tends to limit the common types of diseases; however, the diseases that do occur can be serious.

Disease severity is dependent on the susceptibility of the host, the aggressiveness of the pathogen, and the environment. Cultural management of the host also plays an important role in the severity of disease. Factors influencing the susceptibility of the apple trees include genetic tolerance, tree maturity, vigor (degree of stress), and planting density. Most infectious microorganisms go through a life cycle that includes a period of dormancy. During this period, the organism cannot cause disease. When the pathogen is not dormant, other factors such as its natural state of virulence (aggressiveness) and population density will influence disease severity. Environmental conditions play a key role in disease outbreaks. Disease is most severe when the environment is ideal for infection and disease development.

Diseased trees will produce a variety of symptoms, depending on which part of the tree is attacked (table 1).

Table 1. Symptom expression in diseased apple trees.

Part of Plant		Physiological function		Symptom
affected		impaired			development

Roots, crowns		Uptake and transport of		Poor plant vigor
			water and nutrients		(poor or weak
							growth, chlorosis,
							stunting, tip or
							branch die back,
							loss of leaves or
							flowers, poor fruit
							quality, etc.), loss
							of roots (rot)

Trunk, branches		Damage to cambium		Cankers, dead
			impaired transport of		limbs, girdling
			water and nutrients

Twigs, branches,	Impaired ability to 		Chlorotic or 
blossoms, fruit		manufacture food		necrotic, spots,
							flower loss, poor
							fruit  set , poor fruit
							quality

Growers should monitor trees frequently for symptoms of disease. Watch for indications of stress such as poor growth, branch or twig dieback, yellowing, and discolored or sunken areas on roots, trunk, branches, leaves, or fruit. This type of monitoring may require scraping bark, digging feeder roots, or removing soil around the crown or lateral roots. Keep good records on all phases of orchard management, including routine monitoring for diseases. Record the date of inspection; disease symptoms and signs; environmental conditions; information on recent irrigation, fertilization and chemical applications; and the presence of pests. Sometimes positive diagnosis of diseased trees is not possible at first inspection. Draw a map of the orchard to keep track of suspect trees, which will allow for easy follow-up inspection of suspect trees.

Seasonal and environmental influences on apple tree diseases is great. Some pathogens are only active at certain times of the year. Diseases caused by these organisms are highly dependent on the environment and somewhat less dependent on the degree of host stress. For example, most diseases that affect the flowers, fruit, and leaves are triggered by excess moisture, so the diseases cause problems in the spring during periods of rain, fog, and heavy dew. Some pathogens attack tree roots in the fall; however, symptoms are not visible until the spring when the actively growing tree is unable to take up sufficient water and nutrients. Some pathogens weaken plants year round. These diseases are less dependent on the environment and more dependent on degree of host stress.

The primary goals of a disease management program are to prevent disease outbreaks and to reduce the impact of plant diseases. Often the best approach is to attack the problem by manipulating the plant and its environment. Many pathogens establish themselves slowly over years. Once disease symptoms appear, management options become limited; therefore, the key to effective disease management is prevention. Disease management strategies also must be cost effective.

Disease management begins before the trees are planted. Selecting proper rootstock and cultivars is important in the overall success of the orchard. In selecting trees, make decisions based on market and cultural considerations, but also take into account soil conditions, climate, and the most likely disease problems.

Soil preparation prior to planting will impact tree health and vigor. Apples require deep, level soil with good drainage. Cultivation and amendment of the soil may be necessary to reduce the impact of compacted soil, hardpans, and poor drainage.

Tree establishment and cultural management of the orchard will also affect the overall health and performance of the trees. Careful water and fertilization management are critical in maintaining healthy, vigorous trees. Other important management considerations include sanitation practices, pruning, thinning, harvesting, and pest control. For more information on orchard management, see New Mexico State University Cooperative Extension Guide H-321.

Controlling diseases in apple orchards is difficult once trees are infected. There are no chemical controls available for many diseases, particularly root and crown rots and cankers. Control of these diseases can only be obtained by careful water management and good sanitation practices. Chemical controls are directed at fungal and bacterial diseases of fruit and foliage. The current climate for pesticide registration makes it difficult to maintain a current listing of available materials. Check current chemical references for registration of available fungicides.

Avoid injuring trees, fruit, and beneficial organisms when using pesticides. Copper compounds used to control fungal diseases may cause russeting on developing fruit. Likewise, sulfur compounds used incorrectly may disrupt the natural control of mite pests by destroying predaceous mites. Always read and follow the product label carefully.

Common Apple Diseases In New Mexico Orchards

Powdery Mildew

One of the most common diseases in New Mexico apple orchards is powdery mildew, which is caused by the fungus, Podosphaera leucotricha. The disease occurs during periods of high humidity (above 70%) and warm temperatures. Infected trees develop a white, powdery appearance on the underside of the leaves. This powdery growth is mycelium and spores (conidia) of the fungus. As the infection develops, the disease spreads to twigs, flowers, and fruit. Infected leaves curl upward, and infected fruit develops a net-like russeting on the surface. Late in the season tiny black fruiting bodies (cleistothecia) of the fungus may appear on infected leaves and twigs. Severe infection causes stunted trees with reduced vigor, yield, and fruit quality.

Powdery mildew overwinters as fungal strands (mycelium) in buds infected the previous year. The infected terminals may be silvery-gray in color, stunted, and misshapen. When the buds break dormancy, the new leaves and flowers are infected by the fungus. The powdery fungal growth produced on infected tissue consists of thousands of tiny spores, called conidia, which are responsible for secondary spread and infection. Conidia are disseminated throughout the orchard in wind currents and water splashes. High humidity (greater than 70%) and relatively warm temperatures are required for the conidia to germinate. Although spore germination depends on high humidity, they will not germinate in free water. Thus, while the leaf surface is wet, the fungus is not active. When the water evaporates from the plant surface, the humidity in the plant canopy increases and the fungus becomes active. A new batch of conidia are produced 5 days after infection. In favorable conditions, the disease spreads rapidly.

Conidia are the fungus's short-term survival spore. However, they can withstand hot, dry periods for many weeks. Once the disease begins, it is a potential threat throughout the season. This fungus may also produce fruiting bodies, called cleistothecia, which contain ascospores. These spores are protected from the winter climate. Thus, if produced, the fungus has two mechanisms for overwintering, as dormant mycelium in buds and as ascospores. The disease cycle of apple powdery mildew is illustrated in fig. 1 (Not Available).

Management of powdery mildew on apple begins before the orchard is planted by selecting cultivars with some degree of tolerance to the disease. Highly susceptible cultivars include 'Jonathan', 'Rome Beauty', 'Gravenstein', and 'Mutsu' (Crispin). 'Golden Delicious' and 'Granny Smith' are moderately susceptible. Avoid these cultivars in areas with a history of severe powdery mildew problems. No cultivars are completely resistant to infection. Check with tree producers for information regarding the tolerance of individual cultivars.

Additional management practices include good sanitation practices and protective fungicide spray programs. Sanitation programs should include removing fallen leaves and pruning shoots suspected of infection during dormancy or in early spring. This will help to reduce the primary infection and limit the amount of fungus present in the environment. Routine pruning and thinning are also helpful in allowing good air circulation around the trees, reducing humidity and chances for severe disease development.

In orchards where powdery mildew is known to be a problem, a preventative fungicide spray program can be helpful in controlling the disease. Fungicides are most effective when applied at 7- to 10-day intervals from prepink stage through petal fall. In some areas continued sprays may be necessary until terminal growth stops. A number of registered fungicides control powdery mildew on apple. However, pesticide registrations are constantly changing, making it difficult to compile pesticide lists that will stand up over time. Check with your local county extension service or chemical representative for product availability. Always be sure to read the current label before using any pesticide.

Phytophthora Crown, Collar, and Root Rot

One of the most serious diseases that infects apples is Phytophthora crown, collar, or root rot. This disease is caused by several species of Phytophthora. Crown rot is a disease of the rootstock, affecting bark at the crown (the point where the roots join the stem). When the scion portion of the trunk is affected, the disease is called collar rot. Root rot occurs when the fungus attacks roots away from the crown area. These diseases may occur simultaneously, in any combination, or singly depending on the portion of the tree that is attacked.

General foliar symptoms result from infection by Phytophthora spp. Infected trees exhibit varying degrees of decline:

• Trees will have poor terminal growth.
• Trees become stunted in comparison to non-infected trees.
• The foliage will generally be sparse and yellow.
• Early fall color may occur on infected trees.
• The fruit will be small and color prematurely.

Trees infected with Phytophthora typically decline slowly over many years; however, if infected during an excessively wet spring or fall, the tree may die in the first year.

To see symptoms produced at the collar or crown, the bark must be removed. The underlying tissue is discolored orange-red to brown. Older infections are dark brown to almost black. A distinct margin separates healthy and diseased tissue. Initial infection sites on roots are difficult to see; however, as the disease progresses, the roots decay and become discolored, firm, and brittle. When secondary organisms invade decaying roots, they may become soft.

The speed with which infected trees decline is dependent on several factors, such as the particular Phytophthora species, the tree's age, the type of rootstock and scion, water management, and climatic conditions. In general, younger trees, trees under stress, and trees attacked at the crown are more likely to collapse and die more quickly than older, stronger trees.

Phytophthora spp. are soil-borne fungi that are favored by heavy, wet, poorly drained soils. In the absence of a host plant, the fungus persists in soil for long periods. Severe disease problems occur with heavy rains in late fall through spring, when the soil remains flooded or saturated for a long time. The fungus is most active during relatively cool temperatures. Because disease development is dependent on cool temperatures and high soil moisture, the activity of the fungus is limited during unfavorable conditions. Trees suffering from root rot alone may be able to regenerate roots and recover from infection when the environment is unfavorable for the fungus. In contrast, trees infected with crown or collar rot will not recover once infected, and the tree will eventually die.

Water management is the key to controlling diseases caused by Phytophthora spp. Do not allow water to accumulate around trees crowns! Provide adequate drainage, and avoid planting in heavy soils, low spots, and areas that flood frequently. Once Phytophthora is established in an orchard, it is impossible to eradicate. Therefore, replanting where trees have died from this disease is risky. If trees are replanted in diseased areas, plant them on raised mounds or on broad ridges so that the upper roots are near the soil surface. Always plant with the graft union well above the soil line.

Another important aspect of control is the use of disease-resistant rootstock and scion. This is particularly important in choosing cultivars to replant orchards where Phytophthora has been a problem. Rootstock and scion cultivars will vary in their sensitivity to different Phytophthora spp., therefore every effort should be made to identify the species present in the orchard before replanting.

Fire Blight

Fire blight is a bacterial disease caused by Erwinia amylovora, a bacterium that causes a distinct fire-like appearance on infected plant parts. New shoots are highly susceptible to infection; however, all above-ground plant parts are susceptible to disease.

The bacterium overwinters in cankers and invisible infections on twigs and in buds. In the spring, the bacteria multiplies in infected tissue and begins to ooze from natural openings in the plant. The bacterial cells spread to healthy tissue by water, insects, and pruning tools. Rain, sprinkle irrigation, or high humidity and temperatures between 75 and 85 degrees F provide ideal conditions for infection and disease development. Symptoms develop in spring and summer; hot, dry summer weather generally stops spread and development of the disease.

Apple cultivars vary in their susceptibility to fire blight. Highly susceptible cultivars such as 'Jonathan', 'Gala', 'Fuji', 'Mutsu' (Crispin), and 'Granny Smith' should be avoided in areas known to have a history of the disease.

Cultural practices are important in managing this disease. Removing and destroying infected tissue from trees can go a long way in reducing the severity of the disease. When pruning, cut the branches several inches below visible symptoms, as the bacterium advance through the tissue ahead of symptom development. Clean pruning tools between pruning cuts to avoid inadvertent spread of the bacterium throughout the tree or orchard. Clean tools by dipping them in 70-95% alcohol solution or a 10-50% bleach solution between each pruning cut.

Rapidly growing, young, succulent twigs resulting from excessive tree vigor are particularly susceptible to fire blight. Avoid practices that promote excessive vigor, such as excessive nitrogen fertilization, to reduce the incidence of disease. Proper orchard management practices, including irrigation, fertilization, pruning, thinning, and pest control, will help to maintain moderately vigorous, strong trees that will be less susceptible to bacterium attack.

Antibiotics and copper compounds can be used to control fire blight in orchards with a history of disease. Timing of sprays is critical. Make applications from first bloom to petal fall, but beware of overuse, as copper can damage fruit and bacteria readily develop resistance to antibiotics.

Crown Gall

Crown gall, caused by the soil-borne bacterium Agrobacterium tumefaciens, is an important disease of many plant species and is found in all types of soils worldwide. The bacterium is somewhat unique in its behavior. It stimulates plant tissue to grow and divide abnormally, causing tumor-like galls at infection sites. Gall development impedes the flow of water and nutrients in the plant, resulting in above-ground symptoms of decline and reduced growth.

The bacterium enters the roots, crowns, and branches through wounds created by cultivation, pruning, insects, frost injury, and growth cracks. Once inside the tree, a tumor-inducing plasmid in the bacterium stimulates plant cells to grow abnormally. The resulting tumors, made of plant tissue, are rough in texture and appearance. This disease is sometimes confused with galls produced by woolly apple aphid. However, the woolly apple aphid generally produces more numerous, smaller galls. Additionally, the red-purple insects hidden in a white cottony wax will appear on the trunk of infected trees from spring through fall.

Once a tree is diseased by crown gall, it will eventually die, though the progress of disease development may be slow, causing the tree to linger in a weak state. Decline of infected trees may be slowed by painting above-ground galls with paint containing antibiotics. When treating trees in this manner, it is important not to paint more than 50% of the tree circumference at one time. When trees die, remove and burn the stumps and roots. Wait 2-3 years before replanting.

The best control for crown gall is preventing infection. Plant certified disease-free rootstock, and when planting, take care to avoid injuring the roots and crown. When cultivating around trees be careful to avoid injuring the crown and surface roots. In some cases, the crown and roots may be protected by dipping them in a biological control agent, Agrobacterium radiobacter, prior to planting. A. radiobacter is the same bacterium as A. tumefaciens, but it lacks the tumor-inducing plasmid, thus it is unable to cause disease. A. radiobacter protects the roots and crown by occupying infection sites and thereby excluding the disease-causing bacterium. Unfortunately, A. radiobacter is not effective against all strains of crown gall. Thus, this control practice is not 100% effective.

Alternaria Rot

Alternaria alternata is a common saprophyte ( an organism capable of growth and survival without the aid of another living organism) which can become somewhat infectious to apple fruit that is predisposed to infection because of an injury. Common injuries that can lead to Alternaria rot include mechanical or chemical injury, sunscald, or chilling injury. Infection can occur before or after harvest, although it is more commonly a post-harvest problem.

Alternaria rot is managed by avoiding injury during harvest and packing. Additionally, post-harvest fruit dips in chlorine can help to prevent post-harvest disease problems. Cold storage is another good practice that will reduce disease problems.

Moldy Core

Moldy core is caused by many different species of fungi. This disease is characterized by infection within the locules (the cavity of the ovary or seed cavity), without penetration into the fruit flesh. External symptoms on the fruit are quite subtle, and typically the disease goes unnoticed until the fruit is cut open. External symptoms may include premature ripening, and infected fruit may drop from the tree.

The fungi responsible for this disease colonize the flower parts as soon as the blossoms open. The fungi then enter the developing fruit through an opening in the calyx. Moldy core is primarily a problem during years with light fruit set or in years when dry weather in early summer is followed by heavy rains in late summer. In addition, wet weather during bloom may cause conditions favorable for the fungi to produce spores.

Apple cultivars vary in their susceptibility to moldy core. This difference is primarily related to the presence of the sinus opening at the calyx end of the fruit. 'Delicious', 'Gravenstein', and 'Idared' are susceptible cultivars and should be avoided in areas prone to moldy core problems. In some studies, fungicides used during bloom have been successful in controlling moldy core, but the results are erratic and fungicides are rarely recommended. Cultural practices, such as tree training and pruning (which open up the tree canopy and allow good airflow and light penetration), will help to promote fast drying of plant surfaces, reducing the potential for spore development. These practices should help to reduce the incidence of moldy core.

Nutrient Deficiencies

Nutrient deficiencies result either from a lack of available nutrients (low fertility) or from soil pH that inhibits the uptake of nutrients from the soil. Additionally, an imbalance of nutrients may impair a tree's ability to absorb certain nutrients. Symptoms of nutrient deficiencies vary depending on the deficient element. However, general symptoms include abnormal or reduced growth, discoloration of the foliage and fruit, loss of flowers, reduced yields, and poor fruit quality.

In New Mexico the nutrients most commonly deficient are iron, manganese, and zinc. These elements are relatively unavailable in soils that have a high pH, which is typical of our high-alkaline, low-organic-matter soils.

Iron deficiency, also called iron chlorosis, is identifiable by interveinal chlorosis, where the veins of the leaves remain green while the interveinal areas turn yellow. Severe deficiency may cause white spots or leaf scorch on affected foliage. The symptoms first appear on new growth, but the whole tree may be affected in severe situations. Leaf size is not affected by lack of iron, as happens with zinc deficiency. When iron chlorosis is the result of alkaline soil conditions, as in New Mexican orchards, it is best corrected by acidifying the soil with soil sulfur. As soil pH decreases, the iron in the soil will become available for plant use.

Manganese deficiency symptoms may be similar to those of iron deficiency. The intervienal areas of the leaves become yellow or golden (but will not turn white). As with iron deficiency, a lack of manganese will not affect leaf size. Using acid-forming nitrogen fertilizers usually helps to reduce problems associated with manganese deficiency. Additionally, a foliar spray of manganese sulfate in April can help to alleviate the problem.

Zinc deficiency symptoms develop on the tips of new growth. Leaves are small, stiff, and more narrow than normal--a symptom often called "little leaf." Other symptoms include yellow mottling of the foliage, reduced fruit size and quality, and slow development of lateral branches. In orchards with a history of zinc deficiency, yearly applications of zinc are necessary to control the situation. Zinc is best applied in the spring as the trees are leafing out. Foliar applications are usually more efficient than soil treatments.

Bitter Pit

Bitter pit is a common disorder in apples grown in New Mexico. This physiological disorder is associated with an insufficient amount of calcium in the developing fruit. Bitter pit is not an infectious disease and does not spread from fruit to fruit.

The disorder first appears as small, water-soaked lesions on the surface of the fruit. Gradually, the spots will turn brown and look like bruises. Spots vary in size from 2 to 10 mm, depending on the variety. With time, the spot will become sunken and the underlying tissue spongy. Spots most frequently occur at the calyx end of the fruit, though the entire fruit is susceptible. Fruit is predisposed to bitter pit while on the tree, but while symptoms can develop before harvest, the disorder often does not appear until after harvest. Maximum symptom development usually occurs within 1-2 months in storage. Affected fruit tastes bitter.

Any condition that causes calcium to concentrate in the leaves at the expense of the fruit can cause bitter pit. The disorder is more likely to occur on vigorous upright branches with lots of leafy growth because calcium is diverted away from developing fruit to the rapidly growing leaves. Other factors contributing to bitter pit include variety susceptibility, poor fruit set, excessive nitrogen or potassium fertilization, and a hot, dry growing season. In New Mexico, climate plays an important role in the development of bitter pit. The hot, dry climate typical in many locations causes high rates of evapotranspiration (movement of water through the plant). High evapotranspiration rates cause a diversion of calcium to the leaves at the expense of the fruit. Once calcium gets into the leaves, it is not easily redistributed to the fruit. Additionally, trees that have lost their crop the previous year to frost are more likely to develop bitter pit the following year.

Cultivars vary in their susceptibility to bitter pit. Selection of cultivars may be an important consideration in areas likely to have serious problems associated with the disorder. Apple varieties that are highly susceptible to bitter pit include 'Golden Delicious', 'Jonathan', and 'Granny Smith'. 'Red Delicious' is moderately susceptible. 'McIntosh' and 'Rome Beauty' are fairly resistant to bitter pit.

There is no control for bitter pit once fruit develop symptoms. The best management for this disorder is to use cultural practices that reduce excessive vegetative growth and increase the fruit-to-foliage ratio. Take soil and leaf tissue samples for analysis of nutrient levels and develop a fertilization program according to the orchard's needs. Avoid excessive applications of nitrogen and potassium fertilizer. Avoid heavy dormant pruning, as it results in excessive growth and light fruit set. Summer pruning of vigorous young trees may help lower the incidence of bitter pit. In hot, dry climates, growers should evaluate the potential damage from bitter pit and sunscald and prune accordingly. For example, if sunscald will cause greater losses than bitter pit, prune the trees to encourage moderately vigorous growth.

Other recommended management practices for avoiding heavy losses include avoiding early thinning and overthinning; avoiding early harvest; and storing apples in a cool, climate-controlled environment. In some areas, summer calcium sprays using calcium nitrate or calcium chloride may be effective in managing bitter pit. Apply at least three sprays at one-month intervals beginning mid-June. Take care when applying these materials, as they may cause fruit russeting or leaf burn. Additionally, post-harvest dips in calcium chloride may reduce the amount of bitter pit that develops after harvest.

Watercore

Watercore is similar to bitter pit in that it is an abiotic disorder that does not spread between fruit. This disorder, which causes water-soaked, translucent, glassy cores, is caused by rapid translocation of sugar into the fruit. The disorder is not usually noticeable from the outside of the fruit.

Watercore is most likely to develop on fruit exposed to high levels of heat and sunlight. Additionally, the conditions that favor bitter pit, such as excessive vigor and poor fruit set, also increase the incidence of watercore. Cultural practices that reduce the incidence and severity of bitter pit are also recommended for managing watercore.

The high sugar content of the fruit makes mildly affected fruit good eating quality. Mild watercore symptoms usually disappear after a few weeks in storage. Thus, timely storage of affected fruit can help avoid losses associated with the disorder. Affected fruit should not be stored over six months, as the fruit may begin to develop internal browning.

Salt Injury

Too much soluble salt, such as sodium and chlorine, in the soil or water can adversely affect apple trees by causing burning or scorching on the leaf tips or margins (edges). Water deeply so that accumulated salts leach down to the root zone.

Frost Injury

At maximum dormancy, apple trees can tolerate temperatures well below freezing. However, in early spring as temperatures increase, the plant begins to grow and the young succulent growth is susceptible to frost injury. Mild frost during early development may injure fruit (causing corky ring), twigs, and branches (causing dieback and cankers). Frost later in fruit development can cause internal necrosis. Hard freezes can cause canker damage to larger branches and the trunk. Sap may ooze from cracks caused by low temperatures, a condition called "gummosis."

In areas were freezing temperatures are a serious threat, the likelihood of frost injury may be reduced by conserving heat in the orchard. Keep cover crops or weeds mowed or tilled under. This will help keep the soil surface firm and moist. Experience shows that recently disked orchards or orchards with knee-high ground cover can be considerably colder than an orchard with clean-cultivated, firm, moist floor. In some locations n New Mexico, it may be more important to try to prolong dormancy, thus avoiding injury due to premature bud break. In these areas, ground cover may help by keeping the temperatures a little cooler. Sprinklers or wind machines also may be beneficial in areas with high frost damage.

Sunburn Injury

Sunburn, also referred to as sunscald, affects fruit that are exposed to direct sunlight. the first symptoms of sunburn is the development of yellow or flushed areas on the skin. The discolored areas eventually turn dark while the fruit is still on the tree. This symptom is easy to see, so damage fruit can be avoided at harvest. Another symptom, small yellow spots, are less easy to see and may be overlooked at harvest. The injury is noticed in storage when the spots turn brown.

Sunburn is managed by proper tree training an pruning. In some areas, overhead sprinklers may help to reduce the heat load on developing fruit. However, overhead irrigation can cause other disease problems, so its value in preventing sunburn is probably limited.

Original author: Emroy L. Shannon, Extension Specialist Emeritus.

New Mexico State University is and equal opportunity/affirmative action employer and educator. NMSU and the U.S. Department of Agriculture Cooperating.

Reprinted: April 2000
Electronic Distribution August 2000

Rhizoctonia Disease of Potato

Rhizoctonia solani is a fungus that attacks tubers, underground stems, and stolons of potato plants. Although it probably occurs wherever potatoes are grown, it causes economically significant damage only in cool, wet soils. In temperate production areas, losses from R. solani are sporadic and occur only when weather is cold and wet in the weeks following planting. In northern areas, where growers often must plant in cold soils, Rhizoctonia is a more consistent problem. Poor stands, stunted plants, reduced tuber number and size, and misshapen tubers are characteristic of the Rhizoctonia disease.

Symptoms and Signs

The phase of the disease called black scurf is common on tubers produced commercially and in home gardens. The irregular, black to brown hard masses on the surface of the tuber are sclerotia, or resting bodies, of the fungus (fig. 1). Although these structures adhere tightly to the tuber skin, they are superficial and do not cause damage, even in storage. They do perpetuate the disease and inhibit the establishment of a plant from the tuber if it is used as seed.

Black scurf is the most noticeable sign of Rhizoctonia. But the most damaging phase of the disease occurs underground and often goes unnoticed. The fungus attacks underground sprouts (fig. 2) before they emerge from the soil. Stolons that grow later in the season can also be attacked (fig. 3). The damage varies. The fungal lesion, or canker, can be limited to a superficial brown area that has no discernible effect on plant growth. Severe lesions are large and sunken, as well as necrotic. They interfere with the normal functioning of stems and stolons in translocating starch from leaves to storage in tubers. If the fungal lesion expands quickly, relative to the growth of the plant, the stolon or stem can be girdled and killed.

Damage is most severe at cold temperatures, when emergence and growth of stems and stolons from the tuber are slow relative to the growth of the pathogen. Wet soils also contribute to damage because they warm up more slowly than dry soils and excessive soil moisture slows plant development and favors fungal growth. If Rhizoctonia damage is severe and lesions partially or completely girdle the shoots, sprouts may be stunted or not emerge above the soil. Stolon cankers reduce tuber numbers and size and are identical to shoot cankers in appearance.

Poor stands may be mistaken for seed tuber decay, caused by Fusarium species or soft rot bacteria, unless the plants are excavated and examined. Rhizoctonia does not cause seed decay; its damage is limited to sprouts and stolons. Poor stands and stunted plants can also be caused by blackleg, a bacterial disease that initiates from the seed tuber and progresses up the stems, causing a wet, sometimes slimy, rot. In contrast, Rhizoctonia lesions are always dry and usually sunken.

Late season damage to plants is a direct result of cankers on stolons and stems causing problems with starch translocation. Tubers forming on diseased stolons may be deformed. If stolons and underground stems are severely infected with Rhizoctonia canker, they cannot carry the starch produced in the leaves to the developing tubers. In this case, small, green tubers, called aerial tubers, may form on the stem above the soil (fig. 4). Formation of aerial tubers may indicate that the plant has no tubers of marketable quality below ground.

At the end of the growing season, the fungus produces its sexual state, Thanetephorus cucumeris, on stems just above the soil line. It appears as a superficial delicate white mat which is easily removed (figs. 5 and 6). The fungus does not damage the tissue beneath this mycelium.

R. solani is a specialized pathogen. Only a subset of the isolates of this fungal species can cause cankers on potato. Isolates are grouped by the ability of their hyphae to fuse; isolates that can fuse, or anastomose, are in the same anastomosis group (AG). Isolates that are pathogens of potato are in AG-3. Rarely, isolates in other AG groups can form sclerotia on tubers and mycelial mats on stems. Though not damaging to potato, other AGs of R. solani cause diseases on sugar beet, beans, crucifers, and rice. In the absence of host plants, R. solani can exist by deriving its nutrients as a soil saprophyte from organic debris.

The Disease Cycle

The disease cycle is very straightforward. Inoculum usually is introduced into fields on potato seed tubers, although it may be introduced via contaminated soil. Sclerotia in soil or on seed tubers germinate, and the resulting mycelium colonizes plant surfaces where nutrients are available. Seed inoculum is particularly effective in causing stolon damage because it is so close to developing sprouts. The fungus penetrates young, susceptible tissue, causing cankers that slow or stop the expansion of the infected stem or stolon. Cankers can sever the stolon or shoot from the plant or kill the growing point (fig. 2). The plant's resistance to stolon infection increases after emergence, eventually limiting expansion of lesions. Sclerotia form on tubers and in soil, providing inoculum for other growing seasons.

Disease Management

Getting potato plants to emerge quickly in the spring is key to minimizing damage to shoot and stolon cankers because plants are more susceptible before emergence. Planting seed tubers in warm soil and covering them with as little soil as possible will speed the emergence of the shoots and increase resistance to canker infection. Plant fields with coarse-textured soils first because they are less likely to become waterlogged and will warm up faster.

Crop rotation reduces inoculum that can cause cankers because those R. solani isolates are specific to potato. Sclerotia are relatively resistant to degradation in the soil, however, and may survive for several years in the absence of potato. The fungus can also exist as a saprophyte in soil by colonizing organic debris. The longevity of the population is determined by the initial density of sclerotia at the start of the rotation period, the soil conditions, and the amount of microbial activity in the soil. Planting sclerotia-free seed is an excellent management strategy. Fungicide treatments applied to tubers may help suppress tuber-borne inoculum but are not a replacement for clean seed.

Black scurf, or sclerotia, can be minimized by harvesting soon after vines are killed. Sclerotia begin to form on tubers as vines senesce and become larger and more numerous over time. Therefore, harvesting tubers as soon as possible after skin set reduces tuber scurf significantly. Sclerotia do not form and grow in storage, and there is no increase in tuber storage rot.

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Listing of Factsheets and Information Bulletins regarding Potatoes

ALFALFA

BLISTER BEETLES IN ALFALFA
By Lee Townsend

Several species of blister beetles live in Kentucky. Quite a few specimens have come in this year from tomatoes, which may indicate a higher than normal population in some areas.

Blister beetles are narrow-bodied and 3/4" to 1-1/4" long, with broad heads, and antennae that are about 1/3 the length of the entire body. The front wings are soft and flexible in contrast to the hard front wings of most beetles. Black blister beetle are jet black, striped blister beetle have orange and black stripes on the wing covers, and the margined blister beetle is black with a thin gray stripe around wing covers.

The adults feed on leaves in the tops of a plant but are especially attracted to flowers where they feed on nectar and pollen. They gather in groups, so large numbers can occur in concentrated clusters in a field. These beetles are mid to late summer insects, active in mid-July and early August which translates to the third or fourth cutting.

Blister Beetle Toxicity

Cantharidin is the poisonous substance in blister beetles. Its toxicity is comparable to cyanide or strychnine. Although horses are considered to be very susceptible, comparable doses can poison cattle or sheep. Very small amounts of cantharidin can cause colic in horses. The substance is very stable and remains toxic in dead beetles. Animals may be poisoned by ingesting beetles in cured hay. There is no sampling method that can detect toxic levels of blister beetles in cured hay.

Cantharidin can cause severe skin inflammation and blisters. It is absorbed through the intestine and can cause symptoms such as inflammation, colic, straining, elevated temperature, depression, increased heart rate and respiration, dehydration, sweating, and diarrhea. There is frequent urination during the first 24 hours after ingestion, accompanied by inflammation of the urinary tract. This irritation may also result in secondary infection and bleeding. In addition, calcium levels in horses may be drastically lowered and heart muscle tissues destroyed. Since animals can die within 72 hours, it is imperative to contact a veterinarian as soon as blister beetle poisoning is suspected.

The concentration of cantharidin varies with the species of beetle, as well as sex. The chemical is produced by the male, which has the highest content. Some is passed to the female during mating. Cantharidin content of the striped blister beetle has been measured to be about 5 times greater that the level found in the black blister beetle. The amount of cantharidin necessary to kill a horse is estimated at 1 milligram of cantharidin per kilogram of horse weight. For example, this translates to about 25 striped blister beetles for a 275 pound horse to over 100 for a 1200 pound animal. About 250 and 1,100 of the less toxic black blister beetles would be needed for the same two animal weights.

Hay Management

The best way to deal with blister beetles is through management practices that will keep fields from being attractive. If practical use the first cutting hay for horse feed since the beetles are not active then.

The major step is to cut on a schedule that keeps alfalfa and weeds from producing the flowers that attract beetles and keep them in the field. Cut before an advance bloom stage. This means hay with high quality and protein content and keeps attraction of beetles low. Practice good weed management to keep other flowering plants to a minimum.

Other practices are necessary if flowers and beetles are abundant. The worst thing that can be done is to crimp or crush hay if beetles are present. Crushed beetles remain in the hay and can poison animals. DO NOT use a hay conditioner when harvesting blister beetle infested alfalfa.

Fields with flowered plants can be checked for blister beetles before harvest by using a sweep net as you would to sample for potato leafhoppers. This is not foolproof because large numbers of beetles can be concentrated in very small areas of a field. Collection of 100 sweeps for the field, as would be done for leafhoppers, is not sufficient to be confident that the beetles are not present unless flowering is limited to small areas.

Sickle bar mowers and some of the more modern circular or rotary mowers lay the hay down but do not crush it. Blister beetles have a behavioral characteristic that may be used against them. When plants are disturbed, blister beetles play "possum" and fall to the ground. As the hay dries and cures, the beetles will leave to seek food and moisture.

Horse Owners

Horseowners can reduce the risk of feeding blister beetles to their horses by implementing the following precautions:

+Grow your own alfalfa, if possible, so that you can control all management practices and be sure the crop is beetle free.

+If you do not produce you own hay or need more, buy from a local source and work with that producer to insure that you know what kind of management the hay has had. Develop a good working relationship with your hay producer.

+Set aside or buy hay from the first cutting since it much less likely to have beetles in it. In Kentucky, we see these beetles in the third and fourth cuttings.

+There is no efficient way to inspect hay carefully enough to be sure that it is beetle free or to determine that beetles are below damaging levels before it is fed.

PESTS OF FALL SEEDINGS
By Lee Townsend

Several insects feed on fall-seeded alfalfa, and if numerous and unnoticed, may produce significant stand loss. The most common culprits are fall armyworms, grasshoppers and crickets. Occasionally, Mexican bean beetles and spotted cucumber beetles (southern corn rootworm beetles). Regular inspection of new seedings will allow early detection of pest problems, assessment of damage, and treatment if necessary.

Fall armyworm infestations will tend to be clumped and intense because each female can lay 100 or more eggs in a mass. The small larvae will move out from this focus as they grow and consume all of the nearby plants. Look for roughly circular areas of missing plants. Examine the soil surface for the striped larvae. If needed, spot treatments can be used to deal with the problem.

Grasshoppers and crickets can graze off small seedlings. Damage should appear at the edges of the field and progress across it. These insects will move readily so feeding should be more diffuse over an area. Mexican bean beetles and spotted cucumber beetles also may move in and feed. Their activity should be spread over the field as well.

Evaluate injury carefully. Low rates and spot treatments may be all that is needed to deal with pest activity. See ENT-17 for control recommendations.

Potato

(Solanum tuberosum)

The history of potato cultivation
Distribution of potato
What is it used for?
What are the issues with growing potatoes in Ireland?
GM potato
Global distribution of GM potato

The history of potato cultivation
Potato (Solanum tuberosum) is a member of the Solanaceae family and is closely related to the tomato, pepper, and eggplant. Potatoes originate from South America in the Andes mountains of Peru and Bolivia and have been cultivated for at least 2,400 years; though scientists believe they may have grown wild in the region as long as 13,000 years ago. The Spanish first introduced potatoes into Europe in the sixteenth century after the conquest of Peru and in 1663 potato was established as a field crop in Ireland. Over the years of cultivation the potato became the major food source to the Irish population. In 1845 however, potato blight (Phytophthora infestans) destroyed the Irish potato crop causing the disaster of the Irish Potato Famine when between 1.1 and 1.5 million people died of starvation and famine-related diseases.

On a different dimension, in October 1995, the potato became the first vegetable to be grown in space. NASA and the University of Wisconsin, Madison, created the technology with the goal of feeding astronauts on long space voyages, and eventually, feeding future space colonies .

Distribution of Potato
In 2003, the global area of harvested potato was 19 million hectares, representing production levels of 311 million tonnes (Mt). While global potato production is showing a continuous increase, this rise in output is occurring primarily in developing countries where production is increasing annually by more than 10Mt. In contrast, potato production is declining in developed countries by over 1Mt per annum. As India ranks 3rd after China and Russia in the global potato production, this shows the increasing importance that developing countries place on the global production of potato.

In Ireland; Dublin, Meath, Louth, Cork and Wexford are the five principal potato-growing counties and together they account for 72% of national production area. The trend in regard to area sown (number of hectares of potato sown), yield (tonnes of potato produced per hectare) and production (number of tonnes of saleable product produced) for the period 1995 to 2003 are clearly shown in Figures 1A, 1B and 1C.

Figure 1: Area (A), yield (B) and production (C) of potato (All figures supplied by the CSO)

What is it used for?
The important trait of tuber quality relates to such characteristics as skin finish, defects and processing quality. Combined, all of these determine the end product that will be produced from the potato e.g. whether it is suitable for table use, french frying, crisp making, dehydration or industrial use. In Ireland, presently sown potato varieties are processed for the production of chips, crisps and other snacks, but also dehydrated potato products such as croquettes, potato dumplings, custard powder etc.

As potatoes may be dehydrated, flaked, diced, sliced, peeled, crushed, ground, frozen, and shaped, an enormous array of new potato products are presently being developed for the food, energy and manufacturing sectors. While the waste products from processed potatoes are a disposal problem for the processors, they can also be a valuable source of feed for the livestock industry. Cull potatoes and, in some years, surplus production of potatoes are a source of high-energy feed for livestock . Some alternative, yet unproven, therapeutic uses of potato by-products include the potential to: act as an antacid, antispasmodic, anti-scorbutic or poultice to reduce inflammation; promote healing (cicatrizant); as a diuretic and preventative treatment for heart attacks; to reduce certain eye irritations (an old Creole remedy); to treat neuralgia and as a remineraliser (MSCOMM, 2003).

What are the issues with growing potatoes in Ireland?
The cultivation of potato in Ireland requires significant chemical input to minimise the impact of several disease causing organisms. Some of these include:

• Potato blight or downy mildew (Phytophthora infestans), which can extend rapidly and even cause complete crop loss within a few days. Browning of stems accompanied by lesions cause the destruction of plants at emergence or necrosis at different points on the stem, which is often followed by lodging. Brown spots circled by pale green halos occur on the leaves. A characteristic white mildew develops in conditions of high humidity and is followed by rapid necrosis. Blight is controlled through the destruction of debris and shoots and early preventative treatment prior to the occurrence of symptoms with fungicide sprays. Cultivar choice is also an important factor.

• Pink Rot (Phytophthora erythroseptica) causes infected plants to wilt and collapse as a result of rotting of the crown area of the stem.

• Rubbery Rot (Geotrichum candidum) symptoms are broadly similar to those of pink rot.

• Brown Rot (Ralstonia solanacearum) bacterium can cause wilting of the potato plant with initial symptoms appearing as a brown staining of the vascular ring, which in severe infections, will completely rot away.

• Common Scab (Streptomyces scabies) infection consists of irregular raised tan to brown spots scattered randomly on the tuber.

• White Mold (Sclerotinia) appears as a water-soaked lesion covered by a white, cottony mycelial mat on the leaf or the stem. In severely affected plants, the stem is girdled and the plant will die. Hard, black, irregularly shaped sclerotia (about 0.5 to 1cm in diameter) will then develop inside dying potato stems to ensure that the disease will be able to over-winter.

• Potato cyst nematode (Globodera rostochiensis and Globodera pallida) infestation can be noted by ‘patches’ or rough circular areas of low growth within the crop. Since no curative control method is 100% reliable, preventive measures must be used, which include planting in unaffected (or tested) soil and/or the use of certified seed and crop rotations (minimum of four years) (Chrispeels, 2003) .

• Brown spot or early potato blight (Alternaria alternata) infection initially appears as small dark brown to black spots (1-2mm) on older leaflets on the lower portion of the plant. The spots enlarge and develop concentric rings of raised and depressed necrotic tissue, which gives the lesion a characteristic ‘target spot’ appearance. Advanced lesions often have angular margins because of limitation by leaf veins and a narrow chlorotic halo frequently surrounds the spot. As the disease progresses, affected leaves turn yellow and senesce and either dry up or fall off. Tuber infection occurs less frequently than leaf infection and is usually evident only after several months of storage. Tuber lesions are dark, sunken, irregularly shaped and often surrounded by a raised violet border.

• Silver Scurf (Helminthosporium solani) causes brown blemishes that develop on the tuber surface and lowers the market value of the crop.

• Black scurf (Rhizoctonia) results in delayed emergence, reduced stands and poor tuber quality.

• Black Leg (Erwinia carotovora ssp) causes a soft bacterial decay of lower parts of stems and tubers and which can increase during storage.

• Black Dot causes a potato tuber-blemishing disease. Symptoms are silvery-to-brown patches on the tuber surface; severe infection can cause tuber shrivelling.

Pests of potato can cause considerable economic damage with garden slugs and keeled slugs the most important species. Because of the importance of tuber quality, a relatively small numbers of slugs may cause a significant economic loss in the value of the potato crop. Whereas garden slugs feed both above and below ground, keeled slugs are mainly subterranean which can complicate control measures, as they will not come to the surface where bait is present.

Wireworms are the larvae of the click beetle and crops such as potatoes are particularly susceptible, as wireworms will affect crop quality rather than yield directly by burrowing into the tuber.

Aphids carry potato leaf roll virus (PLRV) and potato virus Y (PVY), which are the more serious viruses to attack potato.

In regards to weed control, volunteer grain, annual grass, certain annual broadleaf weeds and wild oats have to be controlled prior to the potato sowing. Following on from this, control is also required during the first 4 to 6 weeks after the shoots emerge to ensure the crop is able to establish itself.

Nutrients required for good potato growth include Nitrogen, Phosphorus, Potassium, Sulphur, Magnesium and Boron. The main effect of Nitrogen (N) is to increase tuber size but increasing rates of N can reduce tuber dry matter content. High N levels will also delay maturity and increase the incidence of after-cook blackening in some cultivars. Thus, where tuber quality is important it is essential not to use high levels of N. Due to variation in the use of different potato cultivars after harvest, and in the effect of N on tuber quality there is no correct standard rate of N for all cultivars. Thus, potatoes grown for crisps, where high dry matter content is required, should receive reduced amounts of N compared to potatoes grown for french-fries.

GM Potato
The first reported genetic modification of potato was in 1986 (An et al. , 1986; Shanin and Simpson, 1986) . To date, traits incorporated into potato include herbicide tolerance e.g . glyphosate resistance (Hutchinson et al. , 2003) , and fungal resistance [e.g. late blight (Abad et al. , 1997; Guevara-Fujita et al. , 2002; Song et al. , 2003) ]. In addition, several potato varieties have been modified for virus resistance e.g. resistance to potato leaf roll virus (PLRV), potato virus Y (PVY), and potato virus X (PVX) (Harrison, 1992; Fitchen and Beachy, 1993; Wilson, 1993; Baulcombe, 1994; Pierpoint, 1996) .

The genetic modification of potato provides the potential to create varieties with such qualities as:

• Disease resistance e.g. late blight resistance genes have been taken from wild potato varieties e.g. RB gene in ornamental nightshade (Solanum bulbocastanum ) (Song et al. , 2003) .

• Enhanced tuber quality e.g. protein-rich potato to combat malnutrition or reduction of tuber bruising resulting from mechanical damage.

• Altered tuber quality e.g. potato may be modified to produce fructans, which play a role in drought and cold tolerance (Davies, 1996)

• Pharmaceutical production e.g. GM potatoes can be used to generate edible vaccines (Lauterslager et al. , 2001) . These include vaccines for immunity to gastroenteritis (Tuboly et al. , 1999) , cervical cancer (Warzecha et al. , 2003) and bronchitis (Zhou et al. , 2003) .

In the future, the most beneficial modifications to Irish farmers will be for disease and insect resistance and possibly for the production of non-agricultural products.

Global distribution of GM potato
Between 1996 and 2002, the global area of GM potato remained static at less than 0.1%. Currently there are no genetically modified potatoes approved for consumption in Europe, however insect resistant Bt potato has been approved for food use in Canada and Japan, and for environmental release in the US and Canada (EUFIC, 2004) . Several potato varieties have also been modified to resist PLRV, PVY and PVX and some have been approved for food use in Canada and the US (CropBiotech.Net, 2004) .

In the EU a total of 222 environmental releases have occurred (Table 1) and although there has been no commercial planting of GM potato in Europe to date, there is one application pending (Table 2). In addition there have also been sixteen applications for research-related purposes (Table 3).

Table 1: Total number of environmental releases in the EU (European Commission, 2003)

Country	Austria	Belgium	Germany	Denmark	Spain	Finland	France	UK
Potato	2	2	54	10	11	4	12	37
Total	3	122	153	45	245	26	529	226
Country	Greece	Ireland	Italy	Netherlands	Norway	Portugal	Sweden	Total
Potato			7	54		4	25	222
Total	19	4	283	142	1	12	69	1879

Table 2: Commercial applications for release and marketing of GM potato within the EU (European Commission, 2004b)

Notification Number	Member State	Notifier(s)	Name of the product (commercial and other names)	Date of Publication
C/SE/96/3501	Sweden	Amylogene HB;	Potato variety EH92-527-1 with modified starch content	03/02/2003

Table 3: Research applications in the EU (European Commission Joint Research Centre, 2004a)

Notification Number	Member State	Publication	Name of the Institutes or Companies	Project title
B/DE/04/156	Germany	6/21/2004	Max Planck Institute for Chemical Ecology	Ecological relevance of potentially defensive genes during the interaction between Solanum nigrum (Black Nightshade) and environmental factors.
B/IT/03/01	Italy	3/25/2004	Metapontum Agrobios s.c.a r.l.	"Italian Lycopersycon (ITA.LYCO): Biologia avanzata e innovazione di processo al servizio della qualità del pomodoro da industria italiana"
B/SE/04/1101	Sweden	3/19/2004	Plant Science Sweden AB	potato starch with increased amylose content
B/DE/03/155	Germany	3/19/2004	Bavarian State Research Center for Agriculture, Institute for Crop Production and Plant Breeding	Deliberate release of genetically modified marker-free amylopectin-potatoes for verification of starch quality and stability of transferred marker-free sequences under practical field conditions

References:

Abad, M. S., Hakimi, S. M., Kaniewski, W. K., Rommens, C. M., Shulaev, V., Lam, E. and Shah, D. M. (1997) Characterization of acquired resistance in lesion-mimic transgenic potato expressing bacterio-opsin. Molecular Plant-Microbe Interactions 10: 635-645.

An, G., Watson, B. D. and Chiang, C. C. (1986) Transformation of tobacco, tomato, potato and Arabidopsis thaliana using a binary Ti vector system. Plant Physiology 81: 301-305.

Baulcombe, D. (1994) Novel strategies for engineering virus resistance in plants. Current Opinion Biotechnology 5: 117-124.

Chrispeels, M. J. (2003) Life together in the underground. In Plants, genes and crop biotechnology. (eds. M.J. Chrispeels, and D.E. Sadava), Jones and Bartlett Publishers, Sudbury, Massachusetts pp304-327.

CropBiotech.Net (2004) GM potato. ISAAA. Global Knowlegde Centre on Crop Biotechnology. http://www.isaaa.org/kc/

Davies, H. V. (1996) Recent developments in our knowledge of potato transgenic biology. Potato Research 39: 411-427.

Department of Agriculture, F., Aquaculture and Forestry, (2003) Guidelines For Disposal of Cull Potatoes. Department of Environment and Energy. May 2003

EUFIC (2004) Potatoes. The European Food Information Council. Technology & Science. http://www.eufic.org/gb/tech/tech02d.htm

European Commission (2003) Environmental releases of GMOs: Breakdown of summary notifications by plants: Total number of summary notifications circulated on 24/10/2003. Joint Research Centre. http://biotech.jrc.it/deliberate/dbplants.asp

European Commission (2004a) Deliberate release into the environment of GMOs for any other purposes than placing on the market. Joint Research Centre. Biotechnology and GMOs: Information website. http://gmoinfo.jrc.it/gmp_browse_geninf.asp

European Commission Joint Research Centre (2004b) Deliberate releases and placing on the EU market of Genetically Modified Organisms (GMOs): Placing on the market of GMOs as or in products. Biotechnology and GMOs: Information website. http://gmoinfo.jrc.it/gmc_browse.asp

Fitchen, J. H. and Beachy, R. N. (1993) Genetically engineering protection against viruses in transgenic plants. Annual Review of Microbiology 47: 739-763.

Guevara-Fujita, M. L., Rivera, C. and Ghislain, M. (2002) Antifungal proteins used in genetic engineering for late blight resistance. In Late blight: Managing the global threat. Proceedings of Global Initiative on Late Blight Conference. 11-13 Jul 2002 Hamburg, Germany. Global Initiative on Late Blight Conference Proceedings.

Harrison, B. D. (1992) Genetic engineering of virus resistance, a successful genetical alchemy. Proceedings of the Royal Society of Edinburgh 99B: 61-77.

Hutchinson, P. J. S., Tonks, D. J. and Beutler, B. R. (2003) Efficacy and economics of weed control programs in glyphosate-resistant potato (Solanum tuberosum). Weed Technology 17: 854-865.

Lauterslager, T. G. M., Florak, D. E. A., van der Wal, T. J., Molthoff, J. W., Langeveld, J. P. M., Bosch, D., Boersma, W. J. A. and Hilgers, L. A. T. (2001) Oral immunisation of native and primed animals with transgenic potato tubers expressing LT-B. Vaccine 19: 2749-2755.

MSCOMM (2003) Potatoes - Medicinal Properties. M. Serre, http://www.theworldwidegourmet.com/vegetables/potato/medicinal.htm

Pierpoint, W. S. (1996) Modifying resistance to plant viruses. In Genetic engineering of crop plants for resistance to pests and diseases. (eds. W.S. Pierpoint, and P.R. Shewry), British Crop Protection Council, Farnham, UK pp16-37.

Shanin, E. A. and Simpson, R. B. (1986) Gene transfer system for potato. Hortscience 21: 1199-1201.

Song, J., Bradeen, J. M., Naess, S. K., Raasch, J. A., Wielgus, S. M., Haberlach, G. T., Liu, J., Kuang, H., Austin-Phillips, S., Buell, C. R., Helgeson, J. P. and Jiang, J. (2003) Gene RB cloned from Solanum bulbocastanum confers broad spectrum resistance to potato late blight. Proceedings of the National Academy of Science USA 100: 9128-9133.

Tuboly, T., Yu, W., Bailey, A., Degrandis, S., Du, S., Erickson, L. and Nagy, É. (1999) Immunogenicity of porcine transmissible gastroenteritis virus spike protein expressed in plants. Vaccine 18: 2023-2028.

United States Potato Board Potato 101: facts and history. http://www.potatohelp.com/

Warzecha, H., Mason, H. S., Lane, C., Tryggvesson, A., Rybicki, E., Williamson, A. L., Clements, J. D. and Rose, R. C. (2003) Oral immunogenicity of human papillomavirus-like particles expressed in potato. Journal of Virology 77: 8702-8711.

Wilson, T. M. A. (1993) Strategies to protect crop plants against viruses, pathogen-derived resistance blossoms. Proceedings of the National Academy of Science USA 90: 3134-3141.

Zhou, J. Y., Wu, J. X., Cheng, L. Q., Zheng, X. J., Gong, H., Shang, S. B. and Zhou, E. M. (2003) Expression of immunogenic S1 glycopprotein of infectious Bronchitis virus transgenic potatoes. Journal of Virology 77: 9090-9093.

Introduction

Apple scab occurs wherever apples are grown and may be the most serious disease on apples. The disease can also infect crabapple and mountain ash. Scab diseases similar to apple scab occur on pear, firethorn, and hawthorne. The scab-like leaf spots and fruit spots, from which the name was developed, may cause defoliation and reduction in fruit quantity and quality.

Symptoms

The disease may affect leaves, petioles, pedicels, fruit and twigs. The symptomatic spots are most noticeable on leaves and fruit. Infections first appear as olive-green spots with indefinite borders. With age, these spots become more prominent and darken to a greenish-black with a velvety appearance (Figure 1). Severe spotting will cause leaves to senesce and fall off. Spots on young fruit result in deformation and cracking (Figure 2). If infection is severe, the fruit may drop off before ripening. Defoliation may result in a reduction of flower bud formation so that bloom or fruit yield the next year will be reduced.

Disease Cycle

This disease, caused by the fungus Venturia inaequalis (anamorph Spilocaea pomi), may be quite severe when rainy, cool weather occurs in the spring. Fungal spores are produced in early spring on dead, fallen apple leaves about the time buds begin to develop. These spores are splashed by rain and blown by wind to land on developing plant tissue and initiate infections. After spots appear on the newly formed leaves, more spores are produced that spread infection to other parts of the tree. Again, rainy weather greatly encourages spore spread and infection during the secondary phase of spore production. The fungus overwinters on fallen leaves.

Apple Scab disease cycle. (provided by Dr. Wayne Wilcox, Cornell University, NYSAES, Geneva, NY)

Management Strategies

Collect and dispose of fallen leaves in autumn. This will help reduce the inoculum that may cause disease the following spring. A spray schedule with emphasis on the early part of the season is usually required for maximum production of high quality fruit. Applications should be made at pink, bloom, petal fall, and 10-14 days after petal fall. Several products are registered to treat apple scab in New York State. For ornamental plantings, use Serenade or Sysstar WDG. Some fungicides containing the active ingredients chlorothalonil, mancozeb, potassium bicarbonate, or propiconazole are also registered for this use. In the home orchard, use captan, copper, lime sulfur, sulfur, myclobutanil, or Serenade. Some multipurpose spray mixtures may be available that may also help to control other pests. Be certain any formulation(s) of pesticide(s) you purchase are registered for the intended use. Additional information may be available in the publication "Pest Management Around the Home" Part II, Miscellaneous Bulletin S74 (available through Cornell Cooperative Extension). Follow the label instructions for all pesticides used, and avoid the use of insecticides during bloom so that bees are not harmed. Note that sulfur may injure certain apple varieties (MacIntosh, Golden Delicious, Jonathan, and others). Also, myclobutanil may not be registered for all uses on Long Island. For commercial applications, please refer to the appropriate commercial pest management guidelines, or contact your local Cooperative Extension Office for more information on currently registered products.

If plans are underway to plant more apple trees, consider planting cultivars that are resistant to apple scab. These include Enterprise, Goldrush, Liberty, Jonafree, Macfree, Prima, Pristine, Redfree, and Sir Prize.

Several crabapple cultivars show a high resistance to scab and some resistance to some other common diseases of crabapple. These include: 'Adams', 'Adirondack', American Spirit™ ('Amerspirzam'), baccata 'Jackii', 'Cardinal', Centurion® ('Centsam'), 'Dolgo', 'Donald Wyman', 'Doubloons', floribunda, 'Henry Kohankie', 'Indian Summer', 'Liset', 'Ormiston Roy', 'Prairiefire', 'Professor Sprenger', 'Purple Prince', Red Jewel™ ('Jewelcole'), 'Robinson', Royal Raindrops™ ('JFS-KW5'), 'Sentinel', 'Strawberry Parfait', Sugartyme® ('Sutyzam'), x zumi 'Calocarpa'. Many addtional varieties have also shown resistance to scab, but may be highly susceptibel to other dieases or may require further evaluation to fully determine the degree of their resistance to scab.

Updated SLJ, 1/05

This publication contains pesticide recommendations. Changes in pesticide regulations occur constantly, some materials mentioned may no longer be available, and some uses may no longer be legal. All pesticides distributed, sold, and/or applied in New York State must be registered with the New York State Department of Environmental Conservation (DEC). Questions concerning the legality and/or registration status for pesticide use in New York State should be directed to the appropriate Cornell Cooperative Extension Specialist or your regional DEC office. READ THE LABEL BEFORE APPLYING ANY PESTICIDE.
__________________________________________________________________________________
The Plant Disease Diagnostic Clinic at Cornell University is located at 334 Plant Science Building, Ithaca, NY, 14853. Phone: 607-255-7850, Fax: 607-255-4471, Email: kls13@cornell.edu or slj2@cornell.edu

Sooty Blotch, Peltaster fructicola, Geastrumia polystigmatus, Leptodontium elatus

and

Flyspeck, Zygophiala jamaicensis

I. Introduction:

Sooty blotch and flyspeck are surface blemish diseases that commonly appear together on apple or pear in late summer and fall. Although these diseases may shorten the storage life of fruit due to increased water loss, they do not cause decay, and losses are attributed to unacceptable appearance. During wet growing seasons, losses of 25 percent or more are commonly found even in orchards treated with fungicides.

II. Symptoms:

Sooty blotch appears as sooty smudges or olive-green spots on mature fruit (photo 2-28). Individual spots or smudges vary from discreet circular colonies to large lesions with diffused margins. Different colony appearances are attributable to several different pathogens which comprise the disease complex. Flyspeck is characterized by clusters of 10 to 50 sharply defined black shiny specks on the fruit surface (photo 2-29). These superficial colonies are round to irregular and usually measure 1/16 to 1 inch (8-25 mm) in diameter. The individual dots or specks are fruiting structures in which spores are formed that cause secondary spread. Although these diseases may appear separately, they are commonly found together on the same fruit. Typically fruit symptoms are observed by the first of July and become more easily found as the season progresses. There are no significant differences among apple cultivars in susceptibility to these diseases, but symptoms are more apparent on yellow, green, or light colored fruit. Fruits of apple and pear having the thickest cuticle appear to be more severely affected.

III. Disease Cycle:

 These fungi are commonly found on the stem surfaces of many woody plants, including apple shoots. Infections may occur on fruit as early as two to three weeks after petal fall, and are highly favored by frequent rain periods and poor drying conditions. Mycelial growth that forms the sooty blotches can occur in the absence of free water at relative humidity greater than 90 percent. Symptom development of both diseases is relatively slow, typically requiring 20 to 25 days in the orchard, but may occur in 8 to 12 days under optimum conditions. Optimum conditions for conidial production for the flyspeck pathogen are 60 to 70 F (16-21 C) and relative humidity greater than 96 percent.

IV. Monitoring:

At midseason, observe 25 fruit in the interior canopy of sample trees. Symptoms (photos 2-28, 2-29) are more likely to be found in poorly pruned trees in the wetter, foggy, slow-drying areas of the orchard. Expect first symptom expression by early to mid-July. Fungicides should be applied to fresh fruit showing any infections. Presence of these diseases is a good indicator that fungicide surface residues are lacking or very low, and signals potential need for treatment to control these diseases or the decay-producing fungal pathogens.

V. Management:

 The diseases are managed by orchard sanitation and the use of fungicides (Table of effectiveness of apple fungicides). Removing reservoir hosts, especially brambles, from the orchard and surrounding hedgerows helps reduce the amount of inoculum from external sources, but in wet years this practice alone may not be adequate for disease control. Some cultural practices may help prevent the diseases and/or reduce the severity of sooty blotch and flyspeck. These include dormant and summer pruning to open up the tree canopy and thinning to separate fruit clusters. In addition to facilitating the drying of fruit after rain or dew, these practices favor better spray coverage and improve fruit quality. Both diseases are difficult to control in orchards with restricted air movement.

A predictive model for sooty blotch was developed in North Carolina by Turner Sutton. The model is driven by the accumulation of wetting hours beginning 10 days after petal fall. The goal of the model is to help time the first spray for sooty blotch based on the appearance of sooty blotch symptoms.

Credits: Text prepared by A. R. Biggs, from the original text in the Mid-Atlantic Orchard Monitoring Guide (original text by K. D. Hickey and K. S. Yoder). Table of fungicide effectiveness from the 1997 Va./W.Va./Md. Spray Bulletin for Commercial Fruit Growers, table compiled by K. S. Yoder and A. R. Biggs

BEAN        SNAP, LIMA, AND BUTTER BEANS

Phaseolus spp

Bacterial Blights: Halo Blight (bacterium - Pseudomonas syringae pv. phaseolicola); Common Blight (bacterium - Xanthomonas campestris pv. phaseoli): Plants infected with the halo blight bacterium form greenish-yellow circles around each lesion. Interior of the lesion turns brown. With age, lesions enlarge and coalesce. The entire leaf finally drops. Stem lesions appear as long, reddish colored spots. When the plant begins to set fruit, lesions are formed at the nodes which girdle the stem. This reduces fruit development. Common blight-infected pods do not exhibit the greenish-yellow halo around the lesion like halo blight lesions. Infected leaves with halo blight turn yellow and slowly die while those with common blight turn brown and drop quickly. Both organisms are seed-borne. Entry into the plant is through the leaf stomata. Rain and damp weather encourage development of these diseases. Common blight is more of a problem in warm weather while halo blight is favored by cool temperatures. Both bacteria can live in the soil for two years on plant residue. To control bacterial blight of beans, seed grown in the western United States should be planted. Avoid spreading the disease by not entering the field when the foliage is wet. Follow a three year rotation.

Anthracnose (fungus - Colletotrichum lindemuthianum): This is a seed-borne fungus which attacks all above ground portions of the plant. Infected seed are marked by dark, sunken lesions that extend through the seed coat. Stem lesions are oval and sunken. The center of the lesion is dark brown with purplish to red borders. In early stages, the fungus develops along the veins and becomes purplish to red in color. In advanced stages, leaves become ragged. Infection of the pods results in small, reddish, elongated spots. Older spots are sunken and have brown to reddish-brown borders. The disease is favored by cool, wet springs and falls. It disappears during hot, dry summers. The fungus can survive in the soil for two years in plant debris. Control is obtained by: (1) the use of disease-free seed, (2) crop rotation, (3) not entering fields when plants are wet, and (4) spraying with fungicides

Diseases of Apples and Other Pome Fruits

 Fireblight

Fireblight is one of the most destructive diseases of apples, pears, mountain ash and cotoneaster. The bacterium (Erwinia amylovora) that causes this disease attacks both fruit and ornamental plants in the rose family.

Fireblight is most damaging during warm, humid weather, especially during June and July. It is characterized by sudden wilting, followed by shrivelling and blackening of the blossoms, young shoots, and developing fruit. Affected parts look as though they were scorched by fire, hence the name "fireblight." The disease cycle is shown in Figure 1.

Occurrence of the disease is sporadic and unpredictable. It may cause severe damage after being nearly absent for several years.

Symptoms and Disease Development

Any portion of susceptible plants may be attacked. The disease is first observed during the blooming period on the following plant parts:

Blossoms and young fruits. Fireblight causes them to wilt, dry and darken. If the bacteria spread into the fruiting spur, this is called spur blight (Figure 2).

Figure 2. Fire blight spur blight - note dried fruit (arrow). (21KB B&W image)

Tips of young shoots and water sprouts. The terminal growth may be killed back as much as 36 inches, frequently with a bent tip. This is called "shepherd's crook" (Figure 3). Dried leaves remain attached to the dead shoots during summer and fall.

Figure 3. Shepherd's crook on young shoots killed by fireblight. (12KB B&W image)

An infection may progress down a shoot and into the bark of larger limbs where dark, sunken cankers form. These cankers slowly enlarge and eventually may girdle the limb. On pears, mountain ash, and very susceptible apple varieties, trunk cankers often kill the tree.

Bacteria overwinter in cankered limbs. Droplets of sticky amber-colored ooze form on these cankers, called "holdover" cankers. These droplets contain millions of bacteria. Insects, birds, and spattering rain can carry these bacteria to the blossoms, leaves and twigs.

A combination of warm temperatures (65 to 85 degrees Fahrenheit) and high humidity created by rain, fog, or irrigation favors fireblight development. Dry weather usually prevents new infections and retards existing infections. During cool springs, the blossom or spur blight phase usually is not significant. Leaf and twig injury resulting from hail often increases the spread and development of fireblight.

Control

No single practice completely controls fireblight, but a combination of the following practices reduces the chance for infection:

Prune and burn diseased twigs and branches in early spring before budbreak when the trees are not actively growing. At this time the chance of spreading bacteria is minimal. Limited late fall pruning may be satisfactory if done after several hard freezes have occurred. Blighted shoots can be readily located at that time since they retain their leaves after other leaves have fallen. Cut at least 10 inches below the edge of the infected area or canker. After each cut, sterilize the cutting tool and the cut surface with a disinfectant to avoid further spread of bacteria. Household bleach diluted to 20 percent (3 cups to 1 gallon water) and old fashioned liquid Lysol (use only the Regular Lysol in the red box or with the red label, containing o-phenyl-phenol and o-benzyl-p-chlorophenol - this should smell like creosote) diluted to 20 percent are highly effective. Denatured ethyl alcohol (available as shellac thinner) and Pine Sol (19.9% pine oil) are nearly as effective when used full strength. Dip shears, knife or saw in the disinfectant or pour over the cutting edge. Bleach and Pine Sol are very corrosive to tools, so if they are used, be sure to rinse and oil the tools after use to prevent rusting.

Clean cultivation and/or addition of nitrogen fertilizers combined with abundant soil moisture (irrigation or high rainfall) can promote rapid growth of fruit trees. Unless deficiency symptoms occur, avoid the use of fertilizers on young trees, especially where trees are cleanly cultivated, since fireblight is more severe on soft, succulent growth. Use a low-nitrogen balanced fertilizer when tree vigor is low. Tree vigor may be determined by leaf color and the amount of terminal growth produced each season. Twelve to 15 inches of new growth each season is adequate; more encourages fireblight. Remove suckers (water sprouts) as quickly as they develop on susceptible varieties. Their removal often avoids canker formation on the trunk.

Blossoms are the most susceptible part of the tree, but infections in blossoms usually do not continue into the limbs or terminal growth. On trees grown for fruit you can protect blossoms from infection with the antibiotic streptomycin. Follow label directions for application of streptomycin spray. Blossom sprays are not needed for flowering trees grown only as ornamentals.

If you plan to use streptomycin keep in mind the following suggestions:

Use on apple or pear varieties where the disease has been a problem in the past.

Use it at the rate of 100 parts per million (ppm) (1 1/2 teaspoons of a 17-21 percent formulation in a gallon of water).

Make first application in the pink or early bloom stage, and repeat at four- to five-day intervals for a total of three sprays. If the bloom period is prolonged, apply a fourth spray at petal fall or shortly after.

Streptomycin is most effective when used alone, but may be combined safely with lime sulfur, wettable sulfur, benomyl, or captan at peak bloom for scab control.

Do not combine streptomycin with the insecticide Sevin for blossom sprays. Sevin is highly toxic to honeybees and also may result in fruit drop after pollination.

Apply antibiotic sprays as you would spray for other diseases. Thorough coverage from both sides is essential; use about 10 gallons of spray for each mature tree. Spray blossoms thoroughly if daytime temperatures exceed 65 F.

Use after hail.

Do not apply to apples within 50 days of harvest.

Do not apply to pears within 30 days of harvest.

Streptomycin is not registered for use on cotoneaster, crabapple, or mountain ash.

Streptomycin acts systemically; that is, it is taken up by the plant. It is effective for the control of blossom blight. Blossoms that are open when sprayed are protected for three to four days. Streptomycin is much less effective for the control of shoot (twig) blight that occurs later in the season. It is effective if applied immediately after hail.

Uptake of Streptomycin by shoots is enhanced if applied in the evening. Effective control of fireblight is possible through careful pruning and spraying, if you begin before the disease becomes too advanced. In some cases, however, mountain ash, cotoneaster and susceptible apple varieties will not respond to pruning. The disease will continue to spread within the tree or bush, eventually causing the complete loss of the plant.

Resistance to fireblight has been incorporated in several good apple varieties. Those recommended for North Dakota are: Dakota, Haralson, Hazen, Red Duchess, Mandan, Sweet Sixteen, Haralred, State Fair, Northern Lights, Dakota Gold, Woodarz and Red Baron. The older varieties Garrison, Killand and Thorberg are also resistant but are not available in the trade at present.

Crabapples for North Dakota that show good fireblight resistance include Dolgo, Red River, Centennial, Centurion, Jack (or Korean), Siberian, Manchurian, White Candle, Thunderchild, Radiant and Vanguard. The varieties Radiant and Vanguard are susceptible to apple scab. The varieties Spring Snow and Red Splendor show intermediate resistance to fireblight.

Resistant varieties are not immune to fireblight and can be infected in severe fireblight years; however, the level of infection in resistant varieties will be less than in susceptible varieties, which may be destroyed in a severe season. Control measures are more likely to be effective in resistant than in susceptible varieties. There are some reports that the understock used on apples may affect susceptibility. The Malling-Merton and East Malling understocks appear to increase susceptibility over seedling understocks.

Apple varieties that have been reported susceptible to fireblight include: Mantet, Beacon, Wealthy, Lakeland, Honeygold, and Prairie Spy. Crabapple varieties reported susceptible to fireblight include: Almey, Hopa, Strathmore, Purple Wave, Flame, Snowdrift, Whitney, Royalty and Calocarpa (also called Redbud or Zumi).

It is most important to detect blight in the early stages of development and start control measures immediately. After most of the branches of a tree are infected, there is little hope of saving it. In advanced cases of blighted cotoneaster it is better to remove the plant, including the roots, and to start a new one in its place.

Fireblight cankers serve as avenues for entry of canker-causing or wood-decay fungi. Untreated fireblight cankers, especially holdover cankers on larger branches, may serve as infection sites for fungi of two types: those causing death of bark tissue (= canker fungi) and those attacking the wood of the tree (= wood-decay or wood-rot fungi).

Several different pathogenic fungi are capable of infecting through old fireblight cankers. The most commonly encountered in North Dakota is the black rot fungus Physalospora obtusa. This fungus causes perennial cankers which enlarge each year until the branch is girdled. (A more complete description of black rot is given later in this circular.) Black rot cankers which follow fireblight are frequently mistaken for continued damage by fireblight.

Fireblight cankers on main limbs or trunks may also be infected by wood-rotting fungi. The chance of this infection can be reduced by painting exposed wood with an alcohol-base shellac followed by a commercial tree wound dressing such as a water emulsion of asphalt.

Apple Scab and Related Diseases

Apple scab is a common disease on apples growing in North Dakota. The fungus (Venturia inaequalis) that causes this disease is a threat to apple foliage and fruit every year. The same or closely related species of Venturia cause similar diseases on pear, hawthorn, mountain ash and cotoneaster.

Symptoms and Disease Development

Scab produces spots on leaves, petioles, and fruits. On leaves the spots are at first a velvety olive-brown with a feathery margin. Later the spots turn dark brown to black (appear sooty) and have a definite margin (Figure 4). Severe leaf spotting leads to defoliation. Scabs on the fruit have early symptoms similar to those on leaves. Later, fruit scabs become brown and corky-russeted. If infection occurs early, fruits do not expand properly on the infected portions and fruits are undersized and gnarled (Figure 5).

Figure 4. Apple scab on crabapple leaves. (19KB B&W image)

Figure 5. Apple scab on apple fruit. (14KB B&W image)

The apple scab fungus overwinters in dead leaves under the tree. As warmer days begin in the spring, the fungus produces spores in tiny black fruiting bodies embedded in the old leaves. These spores are carried by air currents to newly developing leaves and fruits on the trees, resulting in scab infection (primary infection). Secondary spores are produced on the scabs with subsequent reinfection of leaves and fruits.

Control

Resistance to apple scab differs with varieties. Haralson and Red Duchess are the varieties recommended for North Dakota that are most resistant to scab. Dolgo, Centennial, and Manchurian crabapple are also resistant to scab.

Since the fungus overwinters in infected leaves, the first step in controlling the disease is to clean up and destroy fallen leaves in autumn or early spring. Home-owners can use the fungicides captan or benomyl plus captan during the growing season to prevent infections. Begin at the early bloom period and repeat at seven to 10-day intervals when apple scab is a problem. Sprays act to prevent infections but do not "cure" infections that are already there. Home gardeners may need to initiate a fungicide spray program if scab has caused severe defoliation over several years. This defoliation can seriously weaken trees, reducing the productivity and survival capability of fruit trees as well as the aesthetic value of ornamentals.

Orchardists frequently rely on a rigorous spray schedule to reduce scab to a minimum. Commercial fruit growers should contact the NDSU Extension Service for current recommendations.

Primary spores (ascospores) of Venturia require at least nine hours of continuous wetness on leaves to complete the infection process, while secondary spores (conidia) require at least six hours. These minimum times are at the optimum temperature for infection, between 61 and 75 F. As temperatures go above or below this range, the period of leaf wetness needed increases. The wet periods required are given in Table 1 and are calculated as the average temperature for the wetting period.

Table 1. Approximate hours of wetting at indicated 
temperatures required for leaf scab infection, and days 
required for lesions to appear.
-------------------------------------------------------------
          Hours wetting required for infection*
          ------------------------------------
  			       From secondary	 
             From primary	 inoculum         	
Average	      inoculum		 (conidia)     Days required
 temp.	     (ascospores)	 (summer	for lesions
 (0F)	  (spring infections)   infections)     to appear** 
-------------------------------------------------------------
  78		13	 	   8.7
  77		11		   7.3
  76		 9.5               6.3
 63-75		 9		   5.9		    9
 61-62		 9		   5.9		   10
  60	         9.5		   6.3		   11
 58-59	        10		   6.6		   12
  57	        10		   6.6		   13
  56	        11		   7.3		   13
  55	        11		   7.3		   14
  54	        11.5		   7.7		   14
 52-53	        12 		   7.9		   15
  51	        13		   8.7		   16
  50	        14		   9.3		   16
  49	        14.5		   9.7		   17
  48	        15 		   9.9		   17
  47	        17		  11.3
  46	        19		  12.6
  45	        20		  13.3
  44	        22		  14.6
  43	        25		  16.5
  42	        30		  19.9
 33-41	       >30		 >20.0
-------------------------------------------------------------
* Leaves remain wet for varying lengths of time after the rain 
stops, depending on conditions. Wetting periods from 
intermittent showers should be added together. Average 
temperature for the period should be determined from hourly 
readings.
**Days required for lesions to appear once infection has been 
established. No further wetting is required. For this column 
daily maximum and minimum temperatures are adequate for 
determining the average.
	
(Source: New York State Agricultural Experiment Station 
publications).

Leaves (and fruit) remain wet for varying times following a rain. With daytime showers and normal breezy weather, leaves may dry off quickly, aborting the infection process. When rain occurs in evening or at night, leaves may remain wet all night, especially if there is fog or the air is still. Commercial orchardists use instruments to determine the exact duration of leaf wetness. The home fruit grower can estimate this period.

Under North Dakota conditions the most risky times will be 1) late afternoon or evening rains where skies remain overcast at night and where temperatures are 55 F or higher and 2) rainy-misty days where such conditions persist for 24 hours or more and temperatures are 41 F or higher.

Although most fungicides act primarily to prevent infections, certain fungicides have a few hours of "kickback" activity. This is the period of time after the infection process has started when a fungicide can be applied and still stop an infection. Captan, benomyl plus captan or dodine (available only to commercial orchardists) have 18-24 hours of "kickback" activity against apple scab. If one of these fungicides is applied within 18-24 hours of the start of an infection period (when the tree first becomes wet), the infection can be stopped. Dichlone has a longer "kickback" but is not as readily available to orchardists. Mycobutanil (Nova or Rally) and fenarimol (Rubigan), available to orchardists, have up to 96 hours "kickback" activity.

In our area, dichlone may be available from a few suppliers as Quintar 5F. If Quintar is used at 3.2 fl oz/100 gal. of spray (1/4 teaspoon/gal.), the "kickback" is 30-36 hours; if used at 6.4 fl oz/100 gal. (1/2 teaspoon/gal.), the "kickback" period is 36-48 hours. A "kickback" spray can be used as an emergency treatment when a protective spray was not applied earlier; it should be followed by a protective spray program at the normal 7 to 10-day intervals.

Cedar-Apple Rust and Related Rusts

Cedar-apple rust attacks apples and crabapples. It is caused by the fungus Gymnosporangium juniperi-virginianae.

Several other closely related species of Gymnospor-angium may also attack apple and juniper. These also are found on other trees of the apple family including hawthorn, quince and juneberry. Table 2 lists the species of Gymnosporangium known to occur in North Dakota.

Table 2. Hosts of Gymnosporangium rusts.
---------------------------------------------------------------
				  Prome Fruit Plant 		
		  Juniper Host*	  Part Attacked
---------------------------------------------------------------
Cedar-apple  	    ERC, RMJ      Leaves, fruits of apple. 
rust - G. 
juniperi-
virginianae
Quince rust - 	    ERC, RMJ,     Fruits, especially hawthorn.
G. clavipes	     CJ, BJ		
Hawthorn rust -     ERC, RMJ      Foliage, especially hawthorn;
G. globosum			  also on apples, mountain ash
				  and pear.
Juneberry rust -   RMJ, ERC, CJ   Fruit, stems, leaves of 
G. nidus-avis			  juneberry, quince, apple, 
				  mountain ash.
(No common name)       RMJ	  Hawthorn foliage
 G. bethelii.
(No common name)       BJ	   Juneberry, hawthorn,
G. clavariforme 		  cotoneaster foliage
---------------------------------------------------------------
*ERC = eastern red cedar (Juniperus virginiana)
 RMJ = Rocky Mountain juniper (J. scopulorum)
  CJ = creeping juniper (J. horizontalis)
  BJ = common (Bush) juniper (J. communis)

Symptoms and Disease Development

Cedar-apple rust symptoms develop on both apple leaves and fruits. Small, yellow-to-orange spots develop on the upper leaf surface shortly after bloom. Black dots soon appear in these spots. The infected spots are often thickened or blistered. In mid-summer tiny orange-colored tubes form on the lower leaf surface opposite the spots on the upper surface. These tubes split open and curl back (Figure 6). Heavy infection can result in severe defoliation. Spots on the fruits are similar except that the tubes are not always formed.

Figure 6. Cedar-apple rust on the underside of a hawthorn. The pustules are bright orange. (27KB B&W image)

Like many other rust fungi, cedar-apple rust alternates between two kinds of plants - one being the apple. The alternate hosts (plants on which it completes its life cycle) are red cedar (Juniperus virginiana) or Rocky Mountain juniper (Juniperus scopulorum).

On red cedar, red-brown galls form over a period of nearly two years. In the spring the mature galls ("cedar apples") produce orange gelatinous tendrils ("horns") during moist weather (Figure 7). The spores formed on these tendrils infect apple leaves and fruits. In G. clavipes (quince rust) the galls are elongate, perennial and may live for several years, producing new crops of spores each spring.

Figure 7. Rust gall ("cedar apple") on red cedar. (16KB B&W image)

Control

In commercial orchard practice the disease can be controlled by removing cedars within two miles of apples and crabapples. In cases where this is not practical, apply mancozeb, myclobutanil (Nova or Rally) or fenarimol (Rubigan) periodically, starting when the flower buds show pink and at 14-day intervals to a maximum of three sprays, or until cool wet weather (spring or early summer) is past. This will protect the emerging leaves and developing fruits. Select the more cedar-apple rust resistant varieties such as Dakota, Haralson, Mandan, or Red Duchess. The reaction to other rusts is unknown.

Mancozeb is no longer registered for use in the home garden. Sulfur, registered for scab control, may help to suppress rust development on apple trees grown by the homeowner. Native crabapples are susceptible to cedar-apple rust; Asiatic crabapple varieties are generally resistant. Dolgo, Centennial, and Manchurian crabapples are resistant to cedar-apple rust. The reaction to other rusts is unknown.

In a home garden, removal of galls on junipers by pruning out in late winter may give some control. No species or cultivars of Juniperus are resistant to all of the Gymnosporangium rusts. Many cultivars advertised as resistant are only so to cedar apple rust.

Powdery Mildew

Powdery mildew is potentially a serious problem on apples. On highly susceptible varieties it can cause death of vegetative shoots, death of flower buds, and russetting of fruit. Losses in North Dakota usually are not severe, since most varieties grown are not highly susceptible. Powdery mildew of apple is caused by the fungus Podosphaera leucotricha.

Symptoms and Disease Development

Mildew occurs in the nursery on terminal shoots. On established apple trees it appears on leaves, flowers, shoots, and fruit. On leaves, whitish, felt-like patches of fungus appear and soon cover the leaves (Figure 8). Infected leaves are abnormally narrow and become stiff and brittle with age.

Figure 8. Powdery mildew on leaves. (11KB B&W image)

Blossom buds infected by powdery mildew may winterkill or may open several days after normal buds. Infected shoot buds produce diseased leaves. These leaves are covered with the white fungus from the time they emerge.

Powdery mildew lives over the winter in infected tissues. Infection occurs readily at temperatures of 60 to 80 F whenever the relative humidity is high (no film of moisture is required on the leaf).

Control

In most seasons, no control measures are needed under North Dakota conditions for urban trees. With these conditions, the regular spray schedule for scab and rust will usually give effective control of powdery mildew as well. If powdery mildew becomes a problem, the disease can be controlled by spraying fungicide as soon as the disease appears. Fungicides for home-owners to use are benomyl or wettable sulfur. Commercial orchardists can also use fenarimol (Rubigan) or myclobutanil (Nova or Rally). The fungicide application should begin when the flower buds are in the tight cluster stage and continue until terminal growth stops.

Black Rot-Frogeye Leaf Spot

Two seemingly different but related diseases, frogeye leaf spot and black rot canker, are caused by the same fungus, Physalospora obtusa. Branches or twigs infected with black rot canker are often the source of the spores which infect leaves, causing frogeye leaf spot.

Symptoms and Disease Development

The leaf spot phase is called frogeye leaf spot and starts as small purple spots which may enlarge with concentric zones - hence the name. Older lesions have a pale tan center surrounded by a purplish ring. Frogeye leaf spot shows up mostly when late May and June weather is exceptionally rainy. The black rot fungus also attacks fruit, causing a dry rot. Infected apples eventually shrivel and become black "mummies," hence the name "black rot" (Figure 9). Spores infecting leaves or fruits usually come from undetected or untreated branch cankers.

Figure 9. Black rot mummy and frog eye leaf spot. (15KB B&W image)

Control of frogeye leafspot in the home garden relies on timely pruning of black rot cankers, which are the source of the frogeye leafspot fungus. Orchardists may also use scab fungicides such as mancozeb.

Black rot canker can be especially serious. It is common on crabapples and mountain ash in North Dakota, especially in years after a severe fireblight epidemic or sunscald. This fungus enters through wounds in the bark. Unprotected fireblight cankers or sunscald wounds are especially suitable entry points for black rot. Once established, black rot cankers may girdle large branches or even main stems of young trees. Black rot cankers expand 6-12 inches along the branch each season. This killed bark is discolored and when cut will be brown inside rather than the green or white of healthy bark. On last year's cankers the black rot fungus produces spores profusely in rows of raised black pimples in the bark (Figure 10). These pimples produce large numbers of spores of the black rot fungus.

Figure 10. Black rot on branch. Note rows of black fruiting bodies. (18KB B&W image)

Control

Since spores for the frogeye leaf spot phase come from infected twigs and branches, a necessary first step in preventing leaf spot is careful winter cleanup. Remove dead twigs and branches. Paint cuts with alcohol-based shellac followed by an asphalt-base tree paint. Clean up brush and pruned branches from around and under trees and remove from the area or burn. Remove any black rot mummied fruits hanging on the tree.

As mentioned above, regular sprays used for apple scab control will also protect leaves against frogeye leaf spot. Black rot cankers can be excised and cankered branches removed as for fireblight. Follow the sanitary precautions outlined under fireblight.

Sunscald - Plant Injury

This environmentally-caused problem is very serious on apples, other fruits and other thin-barked trees grown in North Dakota. Sunscald results from winter injury. Apple and mountain ash are two of the most sunscald-susceptible tree species in North Dakota.

Sunscald injury usually occurs in late winter or early spring when bright afternoon sun, plus reflected light from snow, warms the south and southwest side of the tree trunks and branches. The absorption of heat by the dark colored bark activates growth beneath the bark. Damage results when a rapid drop in temperature at sunset kills the activated tissues. The injured areas on the lower branches and trunk turn brown and begin shrinking. Later the bark cracks and peels. Research has shown that late and/or improper pruning of apple trees on south and west sides can lead to increased chances of sunscald.

Young trees that have large sunscald areas on the main trunks may die the following season. Less severe injuries are invaded by canker-causing or wood-rotting fungi if the sunscald wounds are not cared for in a manner to induce rapid healing.

Control

Preventing winter sunscald is an unrelished chore that must be done. The bark must be shaded from the sun's rays. Train young trees by pruning so that the lowest limb is on the southwest side of the trunk and the limb shades the trunk. Various materials may be applied to the south and southwest sides of the trunk. To be effective, these materials must reflect the sun's rays, thus preventing afternoon warming of the trunk in winter. The most effective materials are highly reflective commercial materials similar to household aluminum foil with a fiberglass or polyurethane backing. Household aluminum foil might serve as a substitute, but would not have the insulating properties. White plastic spiral guards may be placed around small tree trunks. These plastic guards are moderately effective but should be removed in the spring to allow normal trunk growth and to prevent the buildup of bacteria and fungi under the guard. One of the simplest procedures is to apply a white, interior latex water-base paint on the south and southwest sides of the trunk. The paint helps to reduce afternoon warming, but is less effective than the other techniques listed above. Lath or boards may also be used to provide shading. Brown kraft paper wraps are not effective.

Sunscald - Fruit Injury

Summer sunscald results when fruit is exposed to the sun's rays during excessively hot weather. Affected fruit becomes brown-skinned and often a corky layer of cells forms beneath the exposed surface.

Other Diseases

Leaf Spots

Several fungi cause blotches or spots on foliage of apples, pears, mountain ash or hawthorn. Except for those already mentioned (rust, scab, frogeye leaf spot, and powdery mildew), leaf spots are generally not serious enough in North Dakota to merit control measures beyond raking up leaves and fallen fruit in the fall and destroying by burning or burying.

If serious leaf spotting causes problems such as early defoliation, sprays may be needed. A laboratory diagnosis of the pathogen involved is needed before proper sprays can be applied. Also compare with scab, rust, frogeye leaf spot, and powdery mildew.

Canker Diseases

Several fungi may infect the bark of branches or main stems causing killed areas in the bark which are called "cankers," Most canker fungi need wounds or injuries to enter. These may be small or large and can be of many types: insect injury, pruning wounds, hail damage, sunscald, or fireblight infection.

Fruit Spots and Rots

Most fruit-rotting organisms need a wound to enter the fruit. Wounds may be from hail, chafing against a branch, or insect feeding. Only minute wounds are needed for rot organisms to enter.

Fruit rots are caused by fungi or bacteria. The exact diagnosis requires laboratory examination. The inoculum for fruit rot infections comes from cankered branches or twigs. Control of fruit rots is best accomplished by careful removal of all such cankers, as described for fireblight. Several fungi cause superficial spots or specks on fruit surfaces. These do not affect the eating quality of the fruit.

Chlorosis

Chlorosis is a common disorder of apple, crabapple, mountain ash and related trees in which the leaves become yellow and are abnormally small. One of the most common forms of chlorosis is iron chlorosis.

In the case of iron chlorosis the leaves become progressively more yellow with green veins. When iron chlorosis is severe, the leaves are small, areas of brown dead tissue form between the veins, and growth almost completely ceases. Iron chlorosis occurs when the iron in the soil is unavailable to the plant. This is a common problem in many North Dakota soils which are alkaline, making the iron unavailable. Iron chlorosis can be treated by using an iron chelate. Spraying the leaves with iron chelate will help the leaves turn green within a few weeks but has little long-term effect. Spading iron chelate into the soil, according to label directions, may correct the problem for several years. Implant capsules are also available and may help correct the problem for several years. These remedies vary in effectiveness and in some cases severe chlorosis responds poorly to treatment.

Chlorosis may be a symptom of root injury or of poor drainage. Waterlogged soil is unsuitable for apples, crabapples, etc. Do not plant in low or poorly drained locations.

Virus Diseases

Several virus diseases are known on pome fruits. Although some are important in large orchard plantings in major fruit growing regions, virus diseases of apples and related trees are seldom encountered in North Dakota. Typical virus symptoms on leaves may be distortion or chlorotic lines, rings, etc. Compare with chlorosis. Some viruses also cause fruit distortion or reduced yield. In North Dakota shoot or leaf distortion is more likely to be caused by herbicide misapplication or drift than by virus. Virus-infected fruit trees cannot be "cured." If the tree is grown primarily for ornamental purposes, the presence of a virus will seldom reduce the tree's value. In orchards, removal and replacement is the only solution.

Root Injury and Damage

One of the most common and yet least recognized causes of tree problems is root disturbance, often associated with some sort of construction activity. An established tree has a wide, spreading root system. Loss of a substantial part of this root system will result in decline of the tree unless corrective measures are taken. Old or very large trees seldom have sufficient regenerative capacity to survive major root damage, although it may take such a tree several years to die.

Changes in grade will also damage tree root systems by upsetting the balance of air and water the roots need to survive. Soil compaction from heavy vehicles can also kill roots. When tree roots are damaged by any of these causes, the tree begins to decline. The first symptom may be leaf scorch. Twigs and shoots die back, then whole branches may die. Death of the tree may follow.

Control

Protect tree root systems, not just the trunk, during construction. Prevent heavy equipment or traffic from traveling near trees. If this is unavoidable, aerate the soil immediately following such activity. Do not allow utility trenching near trees.

If tree roots are damaged, careful pruning to balance top and roots can sometimes help the tree survive. Get the help of a professional arborist. Your city or state forester may recommend someone or offer direct assistance. Water and fertilize to promote vigorous growth.

Decay and Heart Rot

Wood of apples, mountain ash and related trees is very susceptible to decay. Fireblight cankers and sunscald injuries seem to be particularly important sites for infection by decay fungi. Although several fungi cause wood decay in apples and related trees, the most commonly encountered is the fungus Schizophyllum commune. This fungus produces its small (1-2 inch), white, papery or leathery "conks" or "mushrooms" in clusters on infected branches and stems (Figure 11). Once established in a tree, eradication of Schizophyllum is virtually impossible. Removal of the fruiting bodies (conks or mushrooms) has no effect on the progress of the fungus inside the tree. These are the result of the infection, not the cause. Another common fungus causing decay is Polyporus tulipiferae. The control is similar to Schizophyllum.

Figure 11. Fruiting bodies of the heart rot fungus Schizophyllum commune. The white papery 'conks' are 1 to 2" wide. (23KB B&W image)

Control

Protect trees from sunscald. Train trees when young to avoid major pruning later on. Water and fertilize to promote tree vigor which minimizes the damage done by heart rot.

Summary

Control of many of these problems depends on exact diagnosis. Submit samples through county extension offices for diagnosis at the NDSU Plant Pest Diagnostic Laboratory. Before sampling, contact your county extension office for sampling procedures.