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Updated: August 8, 2017
Botrytis at first appears as a white growth on the plant but very soon darkens to a gray color. Smoky-gray "dusty" spores form and are spread by the wind or in water. In greenhouses, any activity will result in a release of spores. Even automated trickle irrigation systems, when turned on, trigger a release of spores. These spores are often found on the outside of seeds. The spores can remain dormant on plant surfaces as long as the life of the plant in some cases. Botrytis forms two types of resting structures on or in infected plant tissue: 1) very dark brown or black multi-celled structures called sclerotia and 2) single-celled, thick, dark walled chlamydospores.
Botrytis must have nutrients or some food source before it invades the plant. Nutrients leaking from wounded plant parts or from dying tissue such as old flower petals provide the required nutrients. From this food base, the fungus becomes more aggressive and invades healthy tissue. A dark to light brown rot forms in the diseased tissue. High humidity conditions favor the growth of this fungus.
Resistance to fungicides containing benzimidazole (FRAC Group 1) is common in greenhouses. These fungicides are unlikely to control Botrytis and are not recommended for that reason. Resistance dicarboximide fungicides (FRAC Group 2) has been found in about 50% of greenhouse operations. Do not rely entirely upon these chemicals for control.
Contact Penn State Extension to obtain information on the fungicides and biological control agents that are currently recommended for use.