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.
Cercospora Leaf Spot (fungi - Cercospora spp.): Lower foliage becomes marked by irregular tan spots one-eighth to one-fourth inch in diameter. Severe infection causes defoliation and plant stunting. It is reported to attack the pod but has only been observed on foliage in Texas. Infection is most severe during periods of extended rainfall, high humidity and temperatures between 75 to 85 degrees F. No resistance exists among varieties. Fungicide sprays should begin at first sign of disease and continued during cool, rainy conditions.
Root Rot (fungus - Rhizoctonia solani): Bean seed may rot in soil or the young seedling may become stunted. A reddish-brown canker is formed on the stem. Cankers may completely girdle the stem or may only partially girdle it, causing severe stunting. Beans should be planted after the soil has warmed to above 69 degreesF. Beans should follow a grass type crop.
Fusarium Root Rot (fungus - Fusarium solani f. sp. phaseoli): Plants infected with Fusarium are characterized by a reddish discoloration of the tap root. Affected plants are stunted with yellow leaves. Young rootlets formed in the area of the lesion are killed. If weather conditions are favorable, a normal crop may be produced. Avoid soils where Fusarium has been a problem. Long rotations (four to five years) will help reduce losses.
Pod Blight (fungus - Diaporthe phaseolorum): Pod blight of lima beans is first observed as brown pustules of irregular shape on the leaves. Lesions grow to one-fourth to three-fourths of an inch in diameter. During the latter part of the growing season, the fungus spreads to nearby pods, where it causes a pale watery spot. The spot enlarges and becomes darker with age. On pods the spot is marked by dark brown to black pustules on the surface arranged in a ring.
Use seed grown in the western United States and use a three- to four-year rotation. Follow a fungicide program to control the disease when it occurs consistently.
Mosaic (virus): Leaves become puckered and mottled with light and dark-green areas. Infected plants become stunted. The virus is seed-borne and can be spread by aphids. Losses can be reduced by growing resistant varieties and following an approved aphid control program.
Curly Top (virus): Infected plants are stunted and have distorted foliage. It is spread by the beet leafhopper. Use resistant varieties and practice good insect control.
Root Knot: (See Root Knot.)
Southern Blight: (See Southern Blight.)
Cotton Root Rot: (See Cotton Root Rot.)
Sun Scald: In the early spring beans are often affected by a condition in which the young leaves turn light tan in color and die. This may happen to the entire leaf or to only a portion of the leaf. The conditions favoring disease development are cool to moderate temperatures, extended periods of high humidity, and cloudy days followed by a bright sunny day. Damage is usually restricted to only a few scattered leaves.
Rust (fungus - Uromyces phaseoli): Small reddish-brown pustules form on lower side of leaves. The fungus overwinters in crop residue. If rust has been severe, a rotation program should be practiced. Resistant varieties should be used when past experience indicates rust to be a problem. Apply approved fungicides at first sign of infection in the fall.
Powdery Mildew (fungus - Erysiphe polygoni): Powdery mildew is character- ized by a white powdery growth on the foliage. Infected pods and foliage become malformed. The fungal spores are spread by wind. Spray with approved fungicides. Powdery mildew seldom becomes an economic problem.
Watery Soft Rot (fungus - Sclerotinia sclerotiorum): The fungus affects the stems, leaves and pods of beans. First signs of infection are small, soft, watery spots that enlarge rapidly under cool, moist conditions. They may enlarge and coalesce and the stem is girdled. Infected pods turn into a soft, watery mass. Following the watery stage the affected tissues dry out and turn brown. Within a short time the brown areas are covered with a dense white fungal growth. With age, the white fungal growth turns gray and is dotted with small, hard black bodies called sclerotia. Most losses occur in shipping. Infected beans tend to stick together.
The disease is favored by temperatures ranging between 60 and 70 degrees F. Long periods of high humidity also favor the development of white mold. Large plants with heavy vine growth encourage disease development.
Sclerotia fall to the ground at maturity where they can lay dormant for as long as ten years. When weather conditions are again favorable, the sclerotia begin growth again. The fungus enters beans directly where pods and leaves come in contact with the developing fungus.
Sclerotia produce small mushroom-like structures which contain thousands of ascospores. The spores are ejected into the air landing on plant parts such as blossoms or decaying leaves and begin to develop. This may be repeated many times resulting in widespread infection.
Every effort should be made to improve air circulation between plants and rows. This can be done by increasing row spacing and decreasing the seeding rate. Excessive applications of nitrogen favor heavy vine growth and should be avoided. During periods of extended cool temperatures and high humidity, fungicides should be applied on a preventive schedule.
Baldhead: Beans emerge and produce cotyledons but nothing is formed above the cotyledonary leaves. This can result from injury from soil insects or fungi, and results from mechanically damaged seed.
Curly Top (virus): Plants infected with curly top die prematurely. Young leaves roll inward and eventually turn yellow and die. (See section on Curly Top.)
Mosaic (virus): Leaves appear puckered and mottled with light and dark green areas. Plants are stunted. Chlorosis occurs on infected leaves.
Powdery Mildew (fungus - Erysiphe polygoni): This is a relatively new disease of both sugar and table beets. Infected leaves are covered by a white, powdery fungal growth. Affected leaves turn red. Sulfur-containing fungicides are recommended.
Root Knot Nematodes: (See Root Knot Nematodes).
Southern Blight: (See Southern Blight.)
Fusarium Yellow (fungus - Fusarium oxysporum f. sp. conglutinans): The first indication of the disease is the yellowish-green color of the foliage. Plants appear wilted and stunted. Infected plants usually show a curved mid-rib and the leaf grows on only one side. The disease may be easily confused with black rot since many symptoms are similar. The fungus can live in the soil for a number of years without a host plant. It infects plants through young rootlets and wounds caused by transplanting or insects. It develops in the water conducting vessels, causing a brown discoloration similar to that produced by the black rot bacterium. The disease is checked by very cold or very hot soil tempera- ture. Resistant varieties and long rotations will avoid crop loss.
Downy Mildew (fungus - Peronospora parasitica): The fungus is more noticeable on the underside of leaves as a gray, fluffy, downy growth in well defined spots. Outer leaves of the head will develop small black spots when infected with the mildew fungus. The fungus overwinters in crop refuse. Sanitation, rotation and spraying with a protective fungicide are the most effective control methods. During periods of high humidity and cool temperature, the fungus is difficult to control and is almost always present in cabbage fields.
Black Leg (fungus - Phoma lingam): First symptoms occur on leaves and stems as small spots with ashen-gray centers and black dots. The stem lesions gradually enlarge extending to the roots. In advanced stages the root system develops a dry rot. Wilted leaves tend to remain attached to the stem instead of defoliating like plants infected with yellows or black rot. The fungus is carried on seed and can persist on infected plant residue for one or two years. Spread is dependent on dew, rain or irrigation water. Avoid soils where cabbage or related plants were grown within the last four years. Destroy crop residues by shredding and deep burial of crop residue.
Powdery Mildew (fungus - Erysiphe polygoni): This disease occurs infrequently on cabbage and related plants. A white, powdery growth is observed on the upper surface of leaves. Protective fungicides can be applied if plants become severely infected.
Alternaria Leaf Spot (fungus - Alternaria brassicae): The first symptom is a minute dark spot on seedling stems and on the leaves. These spots enlarge and are marked with concentric rings, giving a bull's eye appearance. The fungus overwinters on cabbage residue or on seed. Spores are disseminated by wind or water. Hot water treatment, as recommended for black rot, will rid the seed of this organism. Fungicide application will prevent the fungus from developing in the field.
Rhizoctonia or Wire Stem Disease (fungus - Rhizoctonia solani): This disease may appear at different stages of growth. A damping-off phase of the disease will cause young seedlings to die. After seedlings are older, they may be attacked but lesions seldom completely girdle the stems. The infected stems are somewhat smaller than normal and are tough and woody. Older plants can also be attached causing a head rot or a root rot. The causal agent is a common soilborne fungus that attacks many plants. Crop rotation and planting healthy transplants are the most effective means of control.
Internal Tip Burn (physiological): Tip burn causes leaf margins to turn brown. The leaves are buried in the head. Exact nature of the problem has been associated with poor water movement within the plant.
Soft Rot (bacterium - Erwinia carotovora): Soft rot also occurs most commonly when fields become water saturated. Stems become decayed and have a foul odor. During storage and transit, a slimy decay with a foul odor develops. The disease begins in areas that have been bruised, particularly during periods of high temperature and humidity prevail. Proper handling during harvesting, packaging and storing along with keeping temperatures low are the best means of control. Follow a long rotation and plant on raised beds in well drained soil to prevent field infections.
Cabbage Mosaic (virus): Leaves display green and yellow mottled areas. Leaf veins may be lighter in color. Keeping fields and surrounding areas free of weed hosts will help reduce the disease.
Root Knot Nematode: (See Nematodes (Root Knot).)
Southern Blight: (See Southern Blight.)
Powdery Mildew (fungus - Erysiphe cichoracearum and Sphaerotheca fuliginea): This disease appears on the leaves as a white powdery mass composed of the spore-bearing structures of the fungus. Severely infected leaves shrivel and die. The fungus can also grow on petioles and young stems. Infected plants are yellow, stunted, and may die. Fruits are not attacked, but are usually small and deformed. Powdery mildew is favored by cool, dry weather. Spores are air-borne. Varieties of most cucurbits are available that show some degree of resistance to powdery mildew. Preventative fungicide applications will effectively control powdery mildew. New races of the fungus have appeared which are resistant to some fungicides. Several applications at 7 to 10 day intervals may be necessary for optimum control.
Anthracnose (fungus - Colletotrichum lagenarium): First symptoms of this disease are spots on the foliage that begin as yellowish or watersoaked area. Spots enlarge and turn brown to black in color. Diseased tissue dries and the center of the spots fall out, giving the leaf a "shot-hole" appearance. Symptoms on fruits consist of circular, black, sunken, cankers varying in size depending on the host plant. When abundant moisture is present, the center of the spot is surrounded by a gelatinous pink mass. The fungus overwinters on old cucurbit vines and residues. It may also be seed-borne. Plants may be infected at any stage of growth. Disease appearance in the field depends mainly on rainy, cool weather for a period of several days. All above ground portions may be infected. Seed treatment, crop rotation and destruction of crop residues are important practices for the control of this disease. Preventative fungicide applications, as recommended for downy mildew control, should be made at seven to 10 day intervals, or more often, if weather conditions are favorable for disease development. Preventative fungicide applications will protect plants against infection.
Gummy Stem Blight (fungus - Didymella bryoniae): This disease affects leaves and stems, and is more prominent in the crown at soil level. Leaf symptoms begin with irregular spots that dry and drop out giving the lesion a ragged appearance. The most conspicuous phase of the disease is the brown exudation in the crown of infected plants. Vine cankers are found near the soil line, producing a gummy brown ooze. The fungus overwinters in the soil and on crop residue. The fungus is seed-borne. Once the fungus becomes established, millions of spores are produced which can be readily disseminated to other plants by rain, wind or mechanical equipment. Using disease-free seed or seed that has been treated with a fungicide will prevent the disease from becoming established in new fields. Crop rotation should be practiced. Spraying with some fungicides has also shown to be effective.
Angular Leaf Spot (bacterium - Pseudomonas syringae pv. lacrymans): This disease appears on leaves, stems and fruit. Spots are small, angular, straw-colored and watersoaked. Leaf spots often dry and fall out giving the leaf a "shot-hole" appearance, similar to those caused by anthracnose. Spots on fruit are usually smaller and circular in shape. Bacteria overwinter in crop residue and on seed. Hard rains splash the bacteria to stems and leaves. The disease may reach epidemic proportions during periods of heavy rains, particularly if temperatures remain high. Since the disease is seed-borne, the use of disease-free seed treated with a fungicide is recommended. Crop rotation with non-cucurbit crops is also helpful for control of angular leaf spot. Application of copper fungicide will assist in control. Cucurbits, however, are sensitive to copper when young, and repeated applications of copper may cause yellowing of foliage around the edges of the leaves.
Alternaria Leaf Spot (fungus - Alternaria cucumerina): Small, circular watersoaked spots first appear on the leaves, later enlarging to one and one-half inch or more in diameter. Definite concentric rings and margins appear giving the diseased area a "bull's eye" appearance. The fungus overwinters in crop residue and on other cucurbit plants. Numerous air-borne spores are produced on diseased spots. Crop rotation and seed treatment help. A preventative fungicide program should be followed when the disease occurs consistently.
Choanephora Wet-Rot (fungus - Choanephora cucurbitarum): This disease occurs almost exclusively on crenshaw, squash and pumpkins. The blossom ends of fruit turn black, watersoaked, and covered by a fungal growth. The fungus is usually confined to the end of the fruit, but if conditions favorable for disease development prevail, the entire fruit may decay. Greatest damage by this disease is caused during prolonged damp weather.
Fusarium Rind Rot (fungus - Fusarium roseum): Rind rot of cantaloupes caused by Fusarium roseum, caused considerable damage in the Rio Grande Valley in recent years. Rots appear on the melon rind which at first may go unnoticed. However, after peeling the fruit, large brown decomposed areas may be found in the flesh. Since the disease may go unnoticed in the field, melons may be harvested, packed and shipped without the handlers being aware of the problem.
Cucumber Mosaic (virus): This virus causes prominent vein clearing in young leaves, followed by pronounced mosaic mottle on older leaves, and stunting. With cucumber, the fruit is prominently mottled, misshapen and blistered. The virus is spread by aphids. It does not affect watermelon.
Squash Mosaic (virus): This virus does not affect cucumber, cantaloupe, honeydew and watermelon fruit. Symptoms on leaves are faint mottling and distortion. On squash, prominent vein clearing and mottling occurs. Yellow variety fruits are green with isolated yellow zones and misshapen fruit. The virus is spread by the cucumber beetle.
Tobacco Ringspot Virus (virus): Chlorotic stippling, ringspots and mild vein clearing occur on leaves on cantaloupe, honeydew, and cucumber. Squash leaves are severely affected, often showing leaf perforations. Fruit of yellow varieties are severely misshapen with irregular sunken or raised dark green spots. Watermelon plants have shortened internodes and pronounced upright growth of terminals. On fruits, concentric rings and pimples are scattered over the green rind.
Watermelon Mosaic Virus (virus): Vein clearing and mosaic patterns occur on cucumber, cantaloupe, and squash. Older plants are severely stunted and leaves are malformed with dark green blisters. Runners are twisted and stand upright, a symptom expression usually referred to as "snake head." Fruits are small. Squash fruit develop a typical mosaic pattern. Yellow squash are green with yellow spots. Infected zucchini squash are rough and stunted. In cucumbers, the fruit is mottled partially at the stem end. The virus is spread by aphids and possibly other sucking insects. No resistance exists among currently used varieties. Early insect control is important for the prevention of this disease.
Charcoal Rot (fungus - Macrophomina phaseolina): Symptoms resemble those of gummy-stem blight and other vine diseases of melons. First symptoms are dying of leaves close to the crown. As the disease progresses, entire runners wilt and die. Close observation of the crown will reveal brown cankers on the stems both below and above the soil line. Black, hard bodies produced by the fungus, known as sclerotia, are found on the surface of the cankers. Crop rotation may be of limited use since the fungus affects a large number of hosts, including corn and grain sorghum. There appears to be some difference among the varieties. Soil fumigation with either liquid or gas compounds kept for a few days under a plastic cover may offer another means of control.
Fusarium Wilt (fungus - Fusarium oxysporum f. sp. melonis): This is one of the most severe diseases, especially of watermelons, that causes sudden wilting and plant death about the time that fruits are beginning to enlarge. It also attacks the plant at other growth stages especially during the seedling stage when it may produce damping-off. The causal fungus is soil and seed-borne. The disease seems to be most severe when infected seed are used. Serious losses may occur even where watermelons have not been previously grown. Use disease free seed and utilize long rotational programs. Some varieties are more resistant than others.
Root Knot Nematodes (nematode - Meloidogyne spp.): (See nematodes (Root Knot).
See also cantaloupe at NCSU.