Botrytis Blossom Blight

Botrytis blossom blight starts when the pathogen attacks the calyx and flower petals, causing them to wither. As fruit starts to develop, a brown lesion forms where the diseased calyx touched the fruit surface. The lesion quickly spreads over the entire fruit, killing it while it is still very small. Grayish tufts of spores form on infected plant parts.

Decay of flower parts is a serious problem in coastal areas if not controlled. It can become a problem in other growing areas when there is prolonged wet and cool weather during bloom.

Spores form on infected, dead flower parts, fruit mummies on the orchard floor, and on other organic matter such as dead or senescent weeds. In spring, splashing rain and wind spread these spores to opening flowers. Flower parts are infected directly by germinating spores and the pathogen moves into developing fruit from infected flower parts. Green fruit rot develops when damp weather occurs while flower shucks still cling to the surface of young fruit. Cooler weather favors retention of the shucks, which are colonized by the pathogen, and increases the likelihood of green fruit rot.

Weather conditions in coastal districts usually favor Botrytis blight every season, and a fungicide application is recommended at full bloom to prevent serious losses. In other areas, treatment is necessary only when wet weather is expected during bloom.