Botrytis Blight or Gray Mold is caused by the fungus Botrytis cinerea . This fungus is literally everywhere, and affects a broad range of plants. On blueberry, it usually affects blossoms and ripening fruit, although it can cause a stem blight as well. It was first reported on blueberry in New Jersey in 1924. It is usually only a problem when there are cool, wet conditions lasting several days during the blooming period.
Infection usually occurs during bloom.
The infected clusters turn brown , and, if the weather continues to be wet or foggy, they will clump together and become covered with a gray, fuzzy, fungal growth. When the flowers first turn brown, this disease may look like frost damage, but the fungal growth is very distinctive and would be absent from frost damaged plants. The fungus may grow through a stem to the main stem, and may kill the branch above that point. The fungus may grow into developing berries and remain dormant until they begin to ripen, at which point the berries shrivel slightly, and produce the characteristic fungal growth. This can happen after healthy-looking berries have been harvested.