Diseases of Vegetables & Small Fruit
Botrytis gray mold
Botrytis gray mold is a fungus that can start first in flowers, which turn brown and dry. It moves to stalks and leaves, then fruit, causing gray ‘fuzz’ and rotting fruit. Botrytis is common on strawberries, raspberries, Saskatoon’s, and chokecherries. It can also affect vegetables such as broccoli, cauliflower, cabbage, and lettuce. It causes brown, water-soaked areas, which become covered with a gray mold. Spores become air-borne and also spread when handled.
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Cultural Control - Rotate vegetables, planting no vegetables of the crucifer family two years in a row. Make sure soil drains well, don’t over water, and space plants well apart. Water plants in the morning so foliage is dry before nightfall. Our nights are cool, causing moisture to condense on cool foliage, which encourages infection. Greenhouses need good ventilation to reduce humidity and increase air circulation.
- Chemical Control - none registered for domestic use.
Powdery mildew
Powdery mildew causes a white, floury coating of fungal spores on strawberries, raspberries, currants, gooseberries, peas and beans. It affects leaves, young shoots, flowers and fruit, and is most problem in humid, cool weather, and poor light, when it multiplies in moisture on leaves. It is spread by wind in warm dry weather. Leaves are distorted and curl upwards, and severely affected leaves may die. Powdery mildew over winters in leaf debris on soil
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Cultural Control - Prune to encourage air circulation and increase light levels; remove leaf litter, plant disease-resistant cultivars. Baking soda sprayed repeatedly can give some measure of control, but can also increase pH levels, causing iron chlorosis, which is already a problem on raspberries and strawberries in Calgary.
- Chemical Control – Use garden sulfur, copper spray, Folpet (common in insecticide/fungicide sprays for garden use), or Benomyl.
Verticillium wilt fungus
Verticillium wilt fungus affects potatoes, tomatoes, raspberries and strawberries. It enters the plants through roots at flowering time. Lower leaves wilt first and as the fungus moves up the plant; leaves turn yellow, then brown. Only some stems are affected. Verticillium wilt comes from infected seed potatoes, or from infected soil, including soil in which purchased transplants are grown. It can last from two to seven years in soil.
- Cultural Control - Rogue out affected plants, rotate crops.
Fusarium wilt fungus
Fusarium wilt fungus enters potato plant roots from cool, wet soil and causes the lower part of the stem to rot. When warm weather arrives, the plant wilts because water cannot reach top of plant through infected stem, which may be completely girdled. Leaves roll upwards, often turn purple and form tight rosettes. Spores over winter in debris and in infected potatoes saved to be used for seed.
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Cultural Control - Plant resistant varieties; (marked V or F after name on tomato seed packages) Rotate crops, not using the same plants in the same soil for 3-4 years. Rogue out infected plants immediately. Improve soil drainage.
- Chemical Control - none
Damping off
Damping off is caused by several specific fungi which live in the soil and destroy seedlings just before they emerge from the soil, or causes them to collapse as the leaves begin to grow Stems often have a dark, thin, wire-like area near soil level which is narrowed, and prevents moisture from reaching tops of plants.
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Cultural Control - Use sterile soil less mixes for starting seeds, clean containers, thin to prevent overcrowding, do not keep too wet or too cool, rogue out infected plants immediately.
- Chemical Control - ‘No Damp’ is registered for this use.
Tobacco mosaic virus
Tobacco mosaic virus is one of several virus infections causing mottling of leaves and distorted growth of tomatoes; tools and insects mostly spread it.
- Cultural Control - spread by sucking insects, mostly aphids, so insect control is important.. Rogue out all infected plants.
Red leaf of rhubarb
Red leaf of rhubarb refers to two conditions - one bacterial, one viral.
The bacteria causes rotting of the crown until a cavity forms, and dull red leaves. The plant quickly dies.
The virus causes stunted growth and red leaves. The plant dies gradually over several seasons.
There is no cure for either disease - remove plants and plant new ones in a different location.
Blossom end rot
Blossom end rot of tomato and pepper is a cultural problem. Water-soaked areas on the end of the fruit turn dark brown and become dry and leathery. Irregular watering prevents calcium uptake, even though there is plenty in our water and soil, so care taken to maintain sufficient moisture in the soil is essential. It does no good to add extra calcium. Some varieties of tomato are susceptible (Roma, Beefsteak), some are resistant (Early Girl, Champion, Husky Cherry Red).
Potato greening
Potato greening is caused by exposure of the tubers to light - glycoalkaloids occur naturally in the tubers in low concentrations, but increase when exposed to light, and make them taste bitter. Peeling off the green layer makes them edible.
Bacterial speck
Bacterial speck of tomato causes small, dark brown spots on the fruit, which do not extend deeper into the fruit. It is spread by rain and watering.
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Cultural control - grow in sterile potting mix, water soil, not foliage, if possible, and early in the day. Rogue out infected plants, clean tools! Do not plant tomatoes in the same soil as infected plants have grown for at least two years.
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Chemical control - none
Black leaf
Black leaf of Saskatoon is caused by a fungus related to the one causing black knot on Shubert cherries. The underside of the leaves are covered with a black fungal mat. Infected shoots produce witches’ brooms, which enlarge each year. Dead leaves, containing the fungus, remain on the branches over the winter, which infects new growth in the spring. Berry production in affected.
- Cultural control - remove infected branches, clean tools!
- Chemical control - none