Guard Your Vegetable Crops Against Gray Mold
Gray mold is a fairly common problem in tomato and pepper in Florida and can be a major cause of postharvest rot at harvest and in storage. In addition, gray mold can attack beans, cabbage, lettuce, muskmelon, potato, and many ornamentals.
The gray mold fungus, Botrytis cinerea, derives its name from the Greek word “botrys,” meaning a bunch of grapes, which describes the characteristic arrangement of spores. Botrytis can cause a variety of problems including damping-off and blights of flowers, fruits, stems, and foliage. The most common symptom is the sudden collapse of succulent tissue such as young leaves and stems.
Entry often occurs through damaged tissue. Stems can become infected through leaf scars, dead leaves, or other forms of stem damage. Stem lesions appear as large elliptical, water-soaked lesions. These may partially girdle the stem, but sometimes the entire stem is affected and the plant is killed.
Seedlings affected by gray mold may show damping-off with a soft tan-to-brown, water-soaked rot of the stem at or near the soil line or the cotyledons. Leaf lesions develop into wedge-shaped grayish-brown lesions. During cool, moist weather, fungal growth may be evident on infected tissue.
Fruit often are infected at the stem end or shoulder where they contact other infected plant parts. Water-soaked spots appear with a light brown to tan central region. Decay progresses rapidly. Sclerotia may form in infected tissues.
If there is a rapid weather change (not favorable to the fungus), fruit infections may abort. White circular (halo) spots appear on the fruit and are called “ghost spots.” These spots persist on green and mature fruit.
Survival and Spread
The fungus survives between crops as sclerotia or as mycelium in plant debris. Other crops also may serve as sources of inoculum. Development is favored by cool, wet humid weather. Airborne spores landing on tomato plants germinate and can produce an infection when free water from rain, dew, fog, or irrigation is present for prolonged periods.
The fungus does not easily infect healthy intact tissue but generally infects plants through wounded tissue. Senescent flower parts that have fallen onto leaves are a common starting point for leaflet colonization. Leaf lesions often start on senescent tissue or areas of physical or chemical damage.
There is no known resistance to B. cinerea in pepper and tomato cultivars. Avoid wounding plants and fruit during growth. Maintain weed control to minimize periods when plants are wet due to reduced air circulation.
After harvest, disk under crop debris to facilitate rapid decomposition of infected plants.
Fungicide sprays applied before dense canopies are formed with senescing foliage help to control the disease. New specific fungicides for Botrytis are available, but should be rotated with general protectant fungicides to prevent the development of resistance to the new chemical controls.