Guard Your Vegetable Crops Against Gray Mold

gray mold on bell pepper

Gray mold is a weak pathogen that typically enters the plant through wounds or aging tissue. Photo by Joel Allingham, Agricare Inc.

Gray mold (Botrytis cinerea) 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, tomato, strawberry, and many ornamentals.

Identification

In tomato and pepper, the disease cycle often begins when wind or water deposits spores onto a senescing flower. Disease symptoms generally first appear on flowers as gray, fuzzy growth. Blossoms then turn brown and die. As flowers drop into the foliage, lesions develop on leaves, appearing as tan, wedge-shaped lesions largely confined by plant veins. Symptoms appear first on older leaves and then move up the plant to younger leaves.

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Stems often develop a brown, slimy rot when leaf infections progress through petioles.

On fruits, the symptoms start at the base of the calyx with a small round lesion that develops into a soft rot. The fruit becomes covered by a fuzzy mass of gray spores, characteristic of the disease. Infected tomato fruit turn gray-white, soft, and then rot.

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In pepper, fruit may develop light, white halos called ghost spots that occur from airborne spore infection.

Survival and Spread

Gray mold is most severe when temperatures are cool and moisture is abundant. Gray mold can develop fast, and the disease can be devastating in the field causing postharvest losses as well.

Warm, dry weather suppresses disease development. Heavy dew, fog, and frequent rain or irrigation can increase gray mold severity.

The pathogen survives between crops in crop debris and in the soil as spores (conidia) or dormant resting structures (sclerotia), which allows the fungus to survive adverse conditions, or saprophytically on organic matter.

The fungus has a wide host range and can survive pathogenically on alternate host plants, and spores can be blown onto crops from these hosts. Conidia from infected tissue are dispersed by wind and splashing rain. The disease is favored by sufficient humidity in the canopy and, on tomato, is most severe on plants in acidic, sandy soils with high soil moisture.

Management Methods

Since the signs of this fungus may be confused with other saprophytic fungi, the presence of Botrytris by microscopic examination should
be confirmed.

A variety of cultural controls can be used to help manage this disease. For example:

  • Adjust pH by liming acidic soils to provide adequate calcium and maintain uniform soil moisture.
  • Cultivate to incorporate plant debris before planting to reduce survival of B. cinerea.
  • Avoid use of overhead irrigation.
  • Avoid excessive irrigation and fertilization that can lead to dense, lush canopies favorable for gray mold development.
  • Resistance in commercial cultivars is not available.
  • Resistant management strategies on fungicide labels such as tank mixing with another fungicide, rotation of applications, and maximum rate use per application and per season should be followed.

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