Vegetable Diseases

Adapted from: Don Janssen, Extension Educator, University of Nebraska-Lincoln Extension in
Lancaster County; MSU Cares, Mississippi State University Extension Service

Parasitic diseases and nonparasitic (abiotic) disorders can cause serious vegetable losses in home gardens. Effective control depends on differentiating between the two causes and, since no single control measure is effective against all diseases, gardeners must rely on a well-balanced defense to keep diseases in check. Causes:  Garden vegetables can be attacked by a variety of microorganisms (fungi, bacteria, viruses, nematodes). For parasitic disease to occur, plant pathogens must come in contact with a susceptible host plant. Pathogens can be carried to the plants by various means, including transplants, soil, humans, animals, insects, infested seed, and wind or water, alone or in combination. Favorable environmental conditions must be present for the plant pathogen to infect and thrive on the plants. Nonparasitic problems are caused by stress factors—temperature and moisture stresses, nutrient deficiencies or excesses, or herbicide injuries—that can make the plant more susceptible to diseases. Prevention and Treatment:  Insects often transmit diseases by carrying viruses and certain bacteria. Weeds in and around the garden also can harbor disease organisms. Prevention is the best approach to managing plant diseases in the home garden, but sometimes diseases occur despite the best efforts at prevention. Many disease-resistant plant varieties are available to prevent some common diseases. Chemicals are seldom needed and often are not economical for use in the home garden. Chemicals are named in the table by active ingredient. These products may be sold under a variety of brand names. Look at the ingredients to identify the correct product for use. Read and follow the directions on the product label. Identification: One of the first steps in setting up a disease control program is correct identification of disease problems—the earlier the better. With quick action, you can control leaf spots, blights, and mildews within the same season. Other disease problems may not be treatable this season, but correct disease identification allows you to take preventive disease control measures next year. Many garden vegetable diseases are easy to identify. Others may need the advice of someone more experienced. Disease is best identified on plants that are less than 50 percent damaged; do not try to evaluate dead plants. Common vegetable disease symptoms and recommended control measures are provided in the table below. If you cannot identify a disease problem from these descriptions, contact the URI Plant Clinic (http://www.uri.edu/ce/ceec/plantclinic.html) Specific Diseases: Plants from the same family often are susceptible to the same diseases. Therefore, one could expect a disease that attacks many members of the same family to spread through the garden if plants from the same family are planted close to each other and no steps are taken to prevent the disease or to manage it once it appears. Examples of plants by family are: Bean family: beans and peas Beet family: table beet and spinach Cabbage family: broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, mustard greens, kohlrabi, radish, rutabaga and turnip Carrot family: carrot, celery, parsnip Cucumber family: cucumber, cantaloupe, gourds, muskmelon, pumpkin, squash and watermelon Onion family: chive, garlic, leek, onion and shallot Potato family: eggplant, pepper, potato and tomato top of page Asparagus Crown rot (fungus): weak, spindly spears in spring; severely infected crowns may turn a brilliant yellow and show vascular discoloration; feeder roots frequently are rotted. PHOTO Plant healthy crowns in well-drained soil or raised beds. Rust (fungus): elongated orange-red, reddish-brown or black pustules on leaves and stems; fungus overwinters on leaves and stems. PHOTO Remove ferns in the fall; limit overhead watering. Apply mancozeb or wettable sulfur after harvest. Bean Family Anthracnose (fungus): small angular lesions on leaves; lower veins turn black; portions of leaves may wither and turn brown; tiny brown spots on pods that later enlarge, become sunken and darkened with brown to purplish borders; in moist weather, pink sticky spore masses may be produced. PHOTO Use disease-free seed; rotate crops; limit overhead watering; water in morning. Maneb for chemical control. Common blight (bacterium): water-soaked spots on leaves; areas surrounding spots may become yellowish, brown and brittle;  pods have small watery spots that enlarge to irregular blotches; blotches later become brown, sunken and dry. PHOTO Use disease-free seed; limit overhead watering; water in morning. Copper hydroxide for chemical control. Rust (fungus): small red to reddish-brown pustules on undersides of leaves; sometimes on pods; most serious on pole beans. PHOTO Limit overhead watering; water in morning. Maneb or wettable sulfur for chemical control. Seed decay and damping off (fungi):  Pre-emergence and postemergence damping off, root rots, and stem rots. Use treated seed; plant in warm soil. Viruses (bean common mosaic, bean yellow mosaic, cucumber mosaic): symptoms vary with viruses and varieties, but leaves may have irregular light-green areas merging with dark-green patches; leaf puckering or curling; whole plants may be stunted, dwarfed, and sickly yellow. Plant certified seed; control weeds and insect vectors such as aphids and bean leaf beetle. Remove affected plants. Cabbage Family Black leg (fungus): pale spots on leaves and later turn ashen-gray with tiny black specks; spots on stems, dark, sunken, circular to irregular with purple borders;  roots decay; plants may topple over or wilt and die. PHOTO Use four-year rotation between similar crops; use disease-free seed and transplants. Black rot (bacterium): Leaf margins yellow with V-shaped patterns; dwarfed or one-sided plants with yellow to brown leaves; discoloration in vascular rings of stems. PHOTO Use four-year rotation between similar crops; use heat-treated seed and disease-free transplants. Copper hydroxide for chemical control. Yellows (Fusarium wilt) (fungus): foliage takes on lifeless, yellow-green color and curls; lower leaves turn yellow first, then brown and brittle; vascular tissues in stem become yellow to dark brown. PHOTO Rotate crops. top of page Carrot Family Root-knot nematodes: plants stunted and appear deficient in nutrients and water;  small to large galls on roots. Relocate garden; solarize soil. Corn Common smut (fungus): silver swellings or galls on leaves, ears, tassels, or stems enlarge and turn black, breaking open to expose masses of black spores. PHOTO Rotate crops; avoid use of smut-contamin-ated manure; remove smut galls before they break; avoid mechanical injury. Leaf blight (fungus): grayish-green to tan oval lesions on leaves. PHOTO Rotate crops. Rust (fungus): red to brown pustules erupting on upper leaf surface and or stalks. PHOTO Mancozeb or chlorothalonil for chemical control. Stewart's wilt (bacterium): stunting and wilting plants; long, pale-green to yellow streaks in leaves turn brown and dry; premature death of wilted plants. Transmitted by flea beetles. PHOTO Control flea beetles. Cucumber Family Angular leaf spot (bacterium): small, water-soaked spots on leaves become tan on upper surface and gummy or shiny on lower surface; spots take angular shapes and later dry and drop off. PHOTO Use treated seed; avoid excessive nitrogen; limit overhead irrigation; Copper hydroxide or mancozeb for chemical control. Anthracnose (fungus): brown-colored leaf spots; elongated sunken cankers on stems; sunken circular cankers with pink centers and brown margins on fruit. PHOTO Use treated seed; rotate like crops; limit overhead irrigation. Benomyl, maneb, or chlorothalonil for chemical control. Bacterial wilt: plants wilt and die. Transmitted by cucumber beetles. PHOTO Control striped and spotted cucumber beetles; remove affected plants. Downy mildew (fungus): yellowish angular spots on upper leaf surface; white to purplish downy growth on lower leaf surfaces; leaves may curl, turn brown, and die. PHOTO Maneb, chlorothalonil, or mancozeb for chemical control. Fusarium wilt (fungus): vines turn yellow and wilt around fruiting time; vascular tissues of stems appear discolored and may ooze sap. Disease is more prevalent in muskmelons and watermelons. PHOTO Use a three-year rotation. Gummy stem blight (fungus):  plants wilt;  when stems are cut, bacterial ooze strings between the cut stems. Rotate crops; use disease-free seed. Benomyl, chlorothalonil, or mancozeb for chemical control. Viruses (cucumber mosaic, watermelon mosaic, squash mosaic virus): stunted plants with yellow and green mottling of leaves; leaves distorted; fruit mottled, misshapen, warty. Control cucumber beetles and aphids; control weeds. Lettuce Drop (fungus): starts as soft water-soaked spots on stem or near soil surface and spreads up and down; white cottony mass with embedded brown to black bodies on stems. PHOTO Plant in well-drained soil; rotate crops; avoid ground where cabbage or celery has been grown. Onion Family Downy mildew (fungus): spots begin as light areas in leaf margins; whitish mold develops on undersides of leaves; plants become dwarfed and yellowish. PHOTO Plant healthy sets; use a three-year rotation. Maneb or mancozeb for chemical control. Fusarium basal rot (fungus): plants wilt and die; roots have dark-colored rot, fungus invades bulb to cause rot; under moist conditions white mold may develop between seals; under dry conditions, roots may dry and shrivel. Plant in well-drained soil; rotate crops. Neck rot (fungus): exhibits sunken, dry lesions around the neck; inside the bulb may be soft, light-brown with gray powdery-looking mold. A postharvest disease. PHOTO Mancozeb for chemical control. Soft rots (bacterium): begins as onions approach maturity; wet, slimy and foul-smelling rots from neck area down into scale. PHOTO   top of page Pepper Anthracnose (fungus): tan or gray sunken lesions with pink dots on fruit; dark green margins, water-soaked and wrinkled leaves and fruit. PHOTO Limit overhead irrigation. Maneb for chemical control. Bacterial leaf spot (bacterium): spots on leaves are first raised and wartlike, turning into small dark-brown lesions; leaves turn yellow and drop. PHOTO Limit overhead irrigation. Copper hydroxide for chemical control. Blossom end rot (physiological problem):  fruit becomes water-soaked near blossom end; tissues collapse and dry out rapidly, leaving whitish papery area; secondary fungi may invade, turning this area black. PHOTO Water evenly. Cercospora leaf spot (fungus): spots begin as small, circular water-soaked areas that enlarge to gray or white spots with brown to reddish margins; centers may drop out of older spots. PHOTO Maneb for chemical control. Viruses (tobacco mosaic, cucumber mosaic): yellow mottling or streaking of leaves, distortion and dwarfing. Remove affected plants; control insect; vectors; control weeds. Potato Early blight (fungus): dark brown spots on leaves, starting with lower leaves; spots become leathery with concentric rings or "targets." PHOTO Use well-drained soil; rotate crops; reduce plant stress; use balanced fertilizer; limit overhead watering. Chlorothalonil or mancozeb for chemical control. Late blight (fungus): large water-soaked, brown, irregular spots on leaves and stems; undersides of leaves develop white to gray mold under moist, humid conditions; tuber infections and rots can occur. PHOTO Use healthy seed tubers. Chlorothalonil, maneb, or mancozeb for chemical control. Rhizoctonia (fungus): poor stands result from killing of young sprouts; cankers on stems at ground line cause stunting, resetting, and purpling leaves; tubers have superficial black sclerotia closely oppressed on skins. PHOTO Use healthy seed tubers; plant in warm soil. Scab (bacterium): rough, raised corky area randomly across tuber surface, some may be pitted. PHOTO  Plant healthy seed tubers; maintain soil pH at 5.2 or lower; avoid high lime and manure in the spring. Wilts (Fusarium, Verticillium – fungus):  vines turn yellow, wilt and die, often branch by branch; vascular tissues may be discolored. Use healthy seed tubers; rotate crops. Viruses: leaves mottled with light- and dark-green areas; curled or wrinkled leaves; plants dwarfed or distorted. Use healthy seed tubers; remove affected plants control aphids and leafhoppers. Spinach White rust: white pustules on undersides of leaves that produce chlorotic areas on upper leaf surface. PHOTO Destroy weeds that harbor rust. top of page Tomato Anthracnose (fungus): infections begin on green fruit; symptoms most apparent when ripe; small, water-soaked, slightly sunken circular spots on fruit. PHOTO Limit overhead irrigation; stake and space to improve air circulation. Chlorothalonil, maneb, or mancozeb for chemical control. Bacterial spot (bacterium): small, angular greasy spots on leaves and stems; water-soaked spots on fruit often are surrounded by white discoloration. PHOTO Use fungicide-treated seed; sterilize stakes. Copper hydroxide for chemical control. Blossom end rot (physiological disorder):  water-soaked spots on blossom end of green or ripening fruit (may not be noticed until fruit is ripe); spots enlarge and become slightly depressed; spots turn black and rot due to secondary fungi. PHOTO Maintain adequate calcium level by liming if soil test indicates low calcium; maintain an even soil-moisture level; use mulches to retain moisture; do not oversupply nitrogen. Early blight (fungus): dark-brown circular spots with concentric rings, or "targets," on leaves; tissues around spots become yellow; when spots are numerous, leaves wither and dry up. PHOTO Use healthy plants; rotate crops; sterlize stakes; stake and space to improve air circulation; water in morning; mulch.  Chlorothalonil, maneb, or mancozeb for chemical control. Fusarium wilt (fungus): lower leaves yellow and dry; leaves roll up and wilt during hot part of day; inner stem tissues have dark discoloration. PHOTO Use healthy transplants. Herbicide injury (nonparasitic): growing tips curl; leaves distort; veins close together in a parallel fashion; can be confused with virus infections. Use herbicides carefully in or around the garden, especially phenoxy types like 2,4-D; some lawn fertilizers also contain herbicides – check bag before spreading;  do not mulch with herbicide-treated lawn clippings. Seed decay and damping off (fungi): pre- emergence death of seed and post-emergence death of seedlings. Use fungicide-treated seed. Septoria leaf spot (fungus: small, roughly circular spots with dark-brown borders and gray centers on leaves; leaves may die and drop off if heavily infected. PHOTO Use healthy transplants; rotate crops; limit overhead irrigation; water in morning; mulch. Chlorothalonil, maneb, or mancozeb for chemical control. Root-knot nematodes: plants stunted and appear deficient in nutrients and water; small to large galls on roots. Relocate garden; solarize soil; use healthy transplants. Viruses (tobacco mosaic, cucumber mosaic, tobacco streak): causes mottling with light- and dark-green areas in leaves; leaf blades may be distorted and fernlike. Avoid tobacco while working with young plants; wash hands with soapy water before handling plants; control insect vectors. top of page Potato early blight (UConn) Potato late blight (SDState) Potato Rhizoctonia (Cornell) Potato scab (KState) Spinach white rust (WSU) Tomato anthracnose (NYSAESCornell) Tomato bacterial spot (UIllinois) Tomato bloosom end rot (Cornell) Tomato early blight (IAState) Tomato Fusarium wilt (UConn) Tomato Septoria leaf spot (Mobot)

Vegetable Subjects           Fall gardening           Harvesting and Storage           Herbs           Organic gardening           Soil and Mulch           Watering           Weed control     Asparagus crown rot (Vegetablemdonline) Asparagus rust (UMass)   Bean anthracnose (UConn) Bean common blight (UMass) Bean rust (USDA)   Cabbage black leg (NCAT) Cabbage black rot (UConn) Cabbage yellows (UIllinois)   Corn common smut (Ohio State) Corn leaf blight (UIllinois) Corn rust (MSUCares) Stewart's wilt - corn (UMass)   Cucumber angular leaf spot (UGa) Cucumber anthracnose (UMass) Cucumber bacterial wilt (UMass) Cucumber downy mildew (UCDavis) Cucumber fusarium wilt   Lettuce drop (UCDavis)   Onion downy mildew (WSU) Onion neck rot Onion soft rot (WSU)   Pepper anthracnose (NCSU) Pepper bacterial leaf spot (NYSAESCornell) Pepper blossom end rot(UFL) Pepper Cercospora leaf spot (NDSU)