Scott Bauer, USDA Agricultural Research Service, Bugwood.org
Botrytis blight usually starts as a blossom blight, which eventually invades the developing fruits, causing them to rot. This rot can destroy the berry within 48 hours and may appear first at the base of the fruit or when the berry is in contact with the soil, other damp surfaces, or other rotten fruit. As ripening increases and humidity remains high, a characteristic gray, fuzzy coating or web, produced by the fruiting of the fungus, covers the strawberry fruit. As the disease progresses, spores are produced and are easily blown or splashed onto healthy foliage. Once the fungus becomes established, it can produce spores continuously throughout the growing season.
The causal organism, Botrytis cinerea, can live as a parasite as well as a saprophyte on decaying plant debris. Under favorable conditions, the fungus produces spores that are spread by air currents and rain. The flower parts become infected first, and the disease spreads to developing fruit. Gray mold is favored by cold temperatures and high humidity.
Moisture is necessary for the spores to germinate and infect plants; therefore, the disease is favored by high humidity and relatively cool conditions. Practices that help reduce humidity and increase air movement, such as opening up plants by cultivation, controlling weeds, spacing rows and plants farther apart help control gray mold. The fungus thrives on debris, and sanitation is essential for control. Dead plants and fallen leaves should be removed and burned or buried. Some strawberry varieties are less susceptible to gray mold than others.