Regular visits to the garden will help you spot diseased plants before a disease spreads. Here is blossom end rot.
Most vegetable garden diseases can be prevented and controlled. Limit disease damage by identifying diseases quickly and taking action.
Regular visits to the garden will help you spot diseased plants before a disease spreads. Choose the most effective control and then work to prevent future disease outbreaks.
Listed here are 25 common vegetable diseases. The list is in alphabetical order.
To see diseases and pests specific to the crop you are growing, find the crop by name in the Topic Index and click through or check crops by name in the How To Grow archive.
Anthracnose
Anthracnose on tomato
Description. Fungus disease. Over-winters on infected seed, plant debris, or in the soil. Wet weather promotes growth; optimum growth between 78°F and 86°F.
Damage. Dark brown circular sunken spot on stems, leaves, pods or fruit. Centers of lesions may ooze pink spore masses. Reddish discoloration of the leaf veins. Leaves may wither and fall. Plant may die back.
Spread. Over-winters in garden in debris of diseased plants. Spread by wind, rain, animals, gardeners, tools. High humidity, high rainfall, and high temperatures encourage spread. Generally found in eastern North America.
Prevention and controls. Spray or dust with a fixed copper- or sulfur-based fungicide every 7 to 10 days. Remove and discard infected plants. Do not save seed infected planting area; use western-grown seed or seed from areas not infected. Rotate crops. Avoid working in the garden when it is wet which can result in spread of spores. Keep tools clean.
Asparagus Rust
Asparagus rust
Description. Fungus disease of massed reddish or black spores grows on asparagus ferns.
Damage. Tiny, rust-colored spores mass on asparagus ferns. Black spores mass in late summer. Fern growth is retarded. Yield is reduced. High humidity and wet weather encourage spread.
Susceptible plants. Asparagus.
Spread. Rust spores are blown by the wind or carried by gardeners, tools, animals or insects. Spores can over-winter in plant debris. Heavy dew and high humidity encourage this disease. Found throughout North America.
Prevention and controls. Plant resistant varieties. Cut plants to the ground at the end of each season. Remove and destroy plant debris. Keep water off of leaves. Use a preventative sulfur spray or dust every 7 to 10 days until 3 or 4 weeks before harvest.
Bacterial Blight
Bacterial blight bean leaf
Description. Bacterial disease. Most severe where humidity is high for long periods.
Damage. Beans: large brown blotches bordered with yellow or red on leaves of beans. Water-soaked spots on pods. Pea stems turn purple or nearly black near the ground. Small water-soaked spots on leaves; yellow to brown spots on pods enlarge to reddish color.
Susceptible plants. Beans, peas.
Spread. Bacteria enter plants through small openings and wounds. Spread by wind, infected seeds. Over-winters in plant debris. Most severe where humidity remains high for long periods. Found throughout mid-North America, but rarely west of the Rocky Mountains.
Prevention and controls. Remove infected plants and discard them. Bacterial blight can not be cured. Do not save seed from infected area. Rotate crops. Avoid working in the garden when it is wet; this may result in spread of disease.
Bacterial Wilt
Bacterial disease
Description. Bacterial disease that clogs the capillaries transporting water and nutrients through plants. Common in moist soils; active where temperatures are greater than 75°F. Bacteria lives within cucumber beetles and can be transmitted to vine crops through their feces.
Damage. Begins with wilting of a few leaves or a small portion of the vine. Wilt spreads to whole plant within a week or so. When the vine is cut, white ooze will flow from the stem.
Spread. Cucumber beetles, infected seedlings, soil, and water. Disease is most severe in central, southern, and eastern United States.
Prevention and controls. Remove and destroy infected plants before the disease spreads. Control cucumber beetles with rotenone or sabadilla. Wash hands and clean tools with a bleach solution.
Bean Rust
Bean rust on leaves
Description. Fungus disease of reddish orange to brown spore masses that cause leaves to drop.
Damage. Numerous, tiny, rust-colored spots appear on leaves of mature plants. Fungus may first appear as whitish raised spots on the underside of leaves. Leaves turn yellow and die. High humidity and wet weather encourage spread.
Susceptible plants. Beans.
Spread. Rust spores are blown by the wind or carried by gardeners, tools, animals or insects. Spores can over-winter in plant debris. Heavy dew and high humidity favor this disease. Found throughout North America.
Prevention and controls. Plant resistant varieties. Rotate crops. Remove and destroy plant debris. Keep water off of leaves. Spray or dust with a sulfur spray every 7 to 10 days until the disease is controlled.
Blackleg
Blackleg potato plant
Description. A fungus disease resulting in dry rot. Carried on seed and lives in the soil. Most severe in humid or rainy weather.
Damage. Sunken areas develop on lower stem, blacken, and girdle the stem. Gray spots and speck with black dots appear on leaves and stems. Leaf edges wilt and turn bluish or red. Plant wilts and dies.
Susceptible plants. Potatoes.
Spread. Infected seed. Spores can over-winter for 1 or 2 years in plant debris. Rain can spread spores. Tools. Black leg is found in central, southern, and eastern North America.
Prevention and controls. Fixed copper fungicides. Remove and destroy infected plants. Rotate crops. Clean up plant debris.
Black Rot
Bean rust
Description. Bacterial disease encouraged by wet weather.
Damage. Infects young and mature plants. Seedlings turn yellow and die. Mature plants develop wedge-shaped yellow regions and margins which expand to center of leaf. Leaves brown, die, and drop. Vascular tubes in plant turn black and foul smelling. Heads of plants may rot.
Spread. Bacteria over-winters in soil and plant debris. Rain, surface water, and insects can spread disease. Found in central, southern, and eastern United States.
Prevention and controls. Cannot be remedied. Remove and destroy infected plants. Clean garden in fall. Apply micronized sulfur to nearby but uninfected plants ever 7 days until harvest.
Blossom End Rot
Blossom End Rot
Description. Environmental factors cause blossom end rot, not a pathogen. Irregular watering–water, then drought, then water, then drought–particularly when the fruit is forming is one cause. Too much water may also cause blossom end rot. A calcium imbalance in the soil may also result in insufficient water uptake.
Damage. Cells at the end of the blossom fail to receive sufficient water; the blossom end of fruit becomes dry, sunken, and leathery in tomatoes. Peppers can turn brown-black or light-colored and papery at the blossom end. Half of each fruit may be affected.
Prevention and controls. Maintain consistent and even soil moisture. Mulch and cultivate only shallowly during drought. The soil pH should be between 6.0 and 7.0, add limestone which contains calcium if the pH is below 6.0.
Botrytis Rot — Neck Rot
Neck rot onion
Description. Fungus disease that usually attacks onions in storage and over-winters in infected bulbs.
Damage. Leaves become water-soaked, gray to brown. Neck tissue of onions, garlic, and chives become brownish and soft. Dry rot occurs after harvest. Eventually, the entire bulb may rot.
Susceptible plants. Onions, chives, garlic, marjoram, oregano, rosemary, thyme. Sweet onions are most susceptible.
Spread. Fungus over-winters in plant debris. Prolonged wet weather will promote infections.
Prevention and controls. Keep soil healthy and rich. Remove plant debris from the garden at the end of the season. Keep plants leaves dry when watering; water at the base of the plant. Allow plants to mature completely before harvesting. Cure and store onions before storing. Do not store bulbs that have been bruised or damaged.
Clubroot
Clubroot
Description. A fungal disease which lives in the soil and enters a plant through its roots.
Damage. Roots become enlarged and swollen (clubbed) and begin to malfunction. They may crack or rot. Young plants are killed. Older plants have reduced yields. Plants yellow and wilt during the day; leaf heads are small. Plants may recover from wilt at night.
Spread. Fungal spores spread from infected plants by wind, water, or tools. Spores survive for at least 7 years.
Prevention and controls. Remove diseased plants from the garden. Use a 4-year rotation. Clubroot thrives in acid soil; add lime if the soil pH is below 6.0. Raise the pH to 7.2. Grow seedlings in a sterile soil mix.
Corn Smut
Corn smut
Description. Fungus disease causes gray-white galls on corn seedlings, stalks, and ears.
Damage. Whitish-gray galls appear on the ear or other part of corn plant. Galls mature, turn black, and burst releasing thousands of spores.
Susceptible plants. Corn
Spread. Fungal spores are spread by wind or transmitted by humans and tools. Warm dry weather encourages spread.
Prevention and controls. Plant resistant varieties. Remove and destroy galls before galls break open. Apply sulfur- or copper-based fungicide every 7 to 10 days. Remove all crop debris. Rotate crops. Do not compost diseased plants.
Curly Top
Curly top
Description. Curly top is a viral disease. Leaves pucker, curl, and twist. Plant growth is stunted.
Damage. Leaves curl and yellow. Plants become stunted. Fruit does not set or yield is reduced.
Spread. Whiteflies and leafhoppers transmit the virus.
Prevention and controls. Curly top cannot be cured. Plant resistant varieties. Remove and destroy infected plants. Control weeds, insects, and nematodes. Cover plants with row covers if leafhoppers are a problem in the garden.
Damping Off
Damping off
Description. Sclerotinia fungus disease lives in the soil, particularly where is high humidity and warm temperatures.
Damage. Base of the stem near the soil is pinched and bent over causing seedling to die.
Spread. Fungus lives in the soil, primarily in seed beds. Fungus can spread via transported soil or tools. Disease is present throughout North America.
Prevention and controls. Plant in well-drained soil. Use a sterile seed-starting mix. Water seedlings from below. Allow the soil surface to dry before nightfall. Use a fan to keep the air circulating.
Downy Mildew
Downy mildew on grape leaf
Description. A fungal disease that thrives where nights are wet and cool and days are warm and humid. Fungus over-winters in crop and garden debris and spreads through infected seeds.
Damage. Yellowish to light green areas on the surface of older leaves. A felt-like, whitish growth will develop on the underside of leaves. A white, felt-like growth forms on the pods of beans, with a possible reddish discoloration around the white areas. Most common to the eastern US because high humidity and cool temperatures promote spread.
Spread. Spores can be carried by insects, wind, rain, and tools. Spore production is greatest where temperatures are cooler than 65°F and humidity is near 100 percent. Common in the eastern United States where there are cool temperatures and high humidity.
Prevention and controls. Plant resistant varieties. Destroy infected plants and all crop debris. Rotate crops each year. Avoid wetting tops of plants when watering. Spray or dust with a copper-based fungicide every 7 to 10 days until harvest.
Early Blight
Early blight
Description. Fungus disease that over-winters in plant debris.
Damage. Irregular dark spots appear on older leaves followed by a series of concentric dark rings. Spots usually appear on older leaves first. Defoliation can follow. Collar rot at soil level girdles the stems of tomatoes. Cankers or decay can form on fruit and tubers. Warm, wet weather can cause the disease to spread rapidly over the entire plant. Yield is reduced.
Susceptible plants. Celery, potatoes, tomatoes.
Spread. Spores over-winter in plant debris. They can be spread by wind or insects. Spread is encouraged by heavy dew, rainfall, and warm temperatures. Early blight in found throughout North America.
Prevention and controls. Plant healthy seed potatoes and tomato seedlings. Rotate crops. Keep garden free of plant debris. Spray or dust with copper-based fungicide every 7 to 10 days.
Fusarium Wilt
Fusarium
Description. Fungal disease which infects plant vascular tissues. Fungus lives in the soil and infects plants through the roots. Fungus prefers warm, dry weather with soil temperatures between 60°F and 90°F.
Damage. Leaves and stems turn yellow beginning from the base of the plant. Plants wilt and become stunted. Yields are reduced. Plants may die.
Spread. Spores can live in the soil for up to 20 years. Water and striped cucumber beetles can carry the disease. Fusarium wilt is common throughout the United State, particularly from the Rocky Mountain east.
Prevention and controls. Plant disease resistant varieties. Rotate crops. Remove and destroy infected plants. Fungicides are not effective.
Late Blight
Late Blight
Description. Fungus disease that attacks plants after they blossom.
Damage. Water-soaked round spots or patches form on leaves. Leaf spots turn brownish black; a white fungal growth may form on the underside of leaves. Leaf stalks and stems may become soft and blighted.
Susceptible plants. Celery, potatoes, tomatoes.
Spread. Fungus over-winters in plant debris. Seed, water, and wind can carry the disease. Rainy, foggy weather with temperatures between 70°F and 80°F during the day and 20 degrees cooler at night are favorable to late blight.
Prevention and controls. Plant resistant varieties. Plant clean seed potatoes. Rotate crops. Keep garden clean of plant debris. Spray or dust with copper-based fungicide every 7 to 10 days.
Leaf Spot
Leaf spot Septoria
Description. Fungus disease that attacks leaves, also called Septoria leaf spot or Septoria blight.
Damage. Leaves are dotted with small spots, gray on tomatoes or tan to light brown on blackberries. Spot may have purplish borders. As spots enlarge, black dots will appear in the center. The disease may cause leaves to drop.
Spread. Seeds, rain, wind will transmit the disease, also transmitted by working with wet plants. Occurs in central and eastern United States.
Prevention and controls. Plant resistant varieties. Rotate crops. Keep garden free of plant debris. Apply copper dust or liquid copper spray every 7 to 10 days.
Alternaria Leaf Spot
Small yellow spots that appear first on older leaves are a symptom of this fungal blight. These spots gradually enlarge and become dark-colored areas filled with concentric rings.
Alternaria leaf blight is particularly problematic for plants in the cabbage and squash families. Strawberries and carrots are also susceptible. When alternaria infects broccoli and cauliflower plants, it may cause brown areas on the heads. As with most fungal diseases, alternaria thrives in warm, wet weather. The spores are spread by wind and are able to enter leaf tissues when foliage has been consistently moist for 24 hours. The fungus overwinters on plant debris in and around the garden, and can also be transmitted by seed.
Mosaic
Mosaic on tomato
Description. Mosaic, common mosaic and tobacco mosaic: viral diseases that stunts plant growth. Mosaic over-winters in perennial weeds and is transmitted by aphids and cucumber beetles.
Damage. Leaves become mottled yellow and green and may curl and crinkle. Plants are stunted. Yields are reduced. Infected fruit is mottled, bumpy, and misshapen and will ripen unevenly.
Spread. Mosaic cannot be cured. Aphids and spotted or striped cucumber beetles can spread mosaic to susceptible plants. Mosaic over-winters in perennial weeds. The virus can also be spread by people working with infected plants. Mosaic can be found throughout North America.
Prevention and controls. Mosaic can not be cured. Remove and destroy diseased plants. Plant healthy seed. Plant mosaic-resistant varieties. Keep perennial weeds out of the garden. Control aphids and cucumber beetles with insecticidal soap or a light horticultural oil spray. Do not work with plants when they are wet.
Powdery Mildew
Powdery mildew
Description. Fungus disease that lives in soil and plant debris. Encouraged by low soil moisture and high humidity.
Damage. Gray, white, or brown velvety mold grows on surfaces of leaves and young stems. Mold spreads to whole plant. Leaves may yellow and curl then plant may wither and die.
Spread. Over-winters in plant debris, also in apple and plum buds. Spores are spread by water and wind. Found throughout North America.
Prevention and controls. Plant resistant varieties. Remove and destroy infected plants and keep garden clean of plant debris and weeds. Allow space between plants for air circulation. Rotate crops. Disinfect garden tools clean; use one part bleach to four parts water solution. Spray or dust with sulfur or copper-based fungicide every 7 days.
Root Rot
Root rot
Description. Fungus disease that lives in the soil and affects plant vascular system.
Damage. Leaves yellow and lower stems wither. Plants grow unhealthy. Roots covered with mold. Plants do not respond to water and fertilizer.
Susceptible plants. Beans, carrots, corn, peas.
Spread. Fungus lives in the soil. It can be spread with infected soil and by water. Clean tools after use.
Prevention and controls. Remove and destroy infected plants. Plant in well-drained soil. Water less frequently but for longer periods so that water reaches deep in soil. Rotate crops. Raise beds if the soil is too wet. Control harmful nematodes with beneficial nematodes.
Scab
Scab on potato
Description. Fungus disease causes scab-like growth on cucumbers, potatoes, watermelons, peaches, and other fruits.
Damage. Dark, sunken or water-soaked spots on vegetable leaves that result in wilt. Stems can develop cankers. Fruit develops gray, sunken spots. Potatoes develop brown, rough, irregular spots or lesions. Dark, greenish spots appear on half grown apricots and peaches.
Spread. Scab over-winters in garden debris and soil. It is transmitted to plants by the wind. Cool, humid weather encourages spread. Scab is found throughout North America.
Prevention and controls. Plant resistant varieties. Rotate crops. Remove and destroy infected vegetable plants. Keep garden free of plant debris. For fruit trees, use sulfur spray or dust 2 to 3 weeks after petals drop.
Sunscald
Sunscald on peppers
Description. Sunscald is an environmental disorder caused by too much exposure to sun especially during hot, dry weather.
Damage. Large, irregular, paper-like white spots on fruit after prolonged exposure to the sun. White or reddish spots may develop on leaves. Dark molds may grow on scalded areas. Sunscald can occur when leaves drop due to unrelated disease or environmental disorders.
Prevention and controls. Control diseases that cause leaves to drop exposing fruit or stems and trunks to the sun. Plant varieties resistant to diseases which can result in leaf drop. Plant varieties with heavy foliage. Fertilize and water properly.
Verticillium Wilt
Verticillium
Description. Fungal infection of vascular tissues causing wilting. Soil-dwelling fungus infects plants through plant roots.
Damage. Leaves and stems turn yellow. Plants wilt. Stems turn brown. Plant growth is stunted, and yields are reduced.
Spread. Verticillium wilt lives in the soil and over-winters in plant debris. It can spread during cultivation or by running water. Perennial weeds can host verticillium wilt and transmit it to crops.Fungus develops during cool, humid weather.
Prevention and controls. Plant resistant varieties. Practice 4-year rotation. Use a sulfur fungicide ever 7 to 10 days to control disease.
Yellows – Aster Yellows
Yellows on cabbage
Description. Disease caused by mycoplasmas bacteria.
Damage. Leaves turn yellow, then brown, then drop. Plant becomes stunted. Yields are reduced.
Spread. Mycoplasmas over-winters in weeds and other perennial plants. Disease is spread by leafhoppers.
Prevention and controls. Yellows can not be cured. Remove and destroy infected plants. Keep weeds which host leafhoppers cut. Control leafhoppers with diatomaceous earth, insecticidal soap, liquid rotenone or pyrethrum, or horticultural spray oil.
Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.
Stephen Albert
