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Botrytis Blight (Gray Mold)

Botrytis blight is another disease to watch for during prolonged rainy and cloudy periods. Strawberry producers will see it now, but it is also a very common fungal disease on flowers later in the season.

On strawberry plants, one or more blossoms in a cluster will turn brown and die. Light gray masses of dusty Botrytis spores soon appear. Infections are most common in well-protected areas because air movement is light and humidity is high—conditions favoring the fungus. Berries that touch the soil, a decayed berry, or a dead leaf may become soft and light brown with rapidly enlarging lesions. Ripe berries are most susceptible. The berries soon dry out and become a dark brown “mummy” covered with the typical gray, dusty powder of spores, which give this disease the name gray mold. You likely have seen Botrytis on berries that were not consumed quickly enough or not refrigerated.

Fungicides protect the blossoms and ripening fruit of strawberry. Initiate sprays during early bloom and repeat at seven- to ten-day intervals through the fruit-ripening period. Multipurpose fruit spray plus captan or Benlate is recommended for home-grown strawberries infected with Botrytis. Commercial growers should consult the Illinois Commercial Small Fruit and Grape Spray Guide, #MD-1.

Control measures for gray mold will also help control some of the other fungal diseases that infect strawberry. Avoid heavy applications of nitrogen in the spring. Mulch plants and between rows with clean straw, hay, other dry organic matter, or landscape cloth to keep berries from contacting the soil. Pick fruit frequently and carefully, early in the day but after the plants are dry, to avoid spreading the causal fungus. For the same reason, cull all diseased berries.

For more information on Botrytis of strawberry, consult Report on Plant Diseases No. 704. Botrytis of ornamental plants is discussed in RPD No. 623.

Author: Nancy Pataky


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