Blossom End Rot of Apple

Blossom end rot of apple is not a major problem in Pennsylvania orchards. Because it occurs only infrequently, very little is known about its cycle and control.

The disease, caused primarily by the fungus Botrytis cinerea, attacks the blossom end of apple fruit (a severe bunch rot of grape is caused by the same organism). The infection is likely to occur during bloom, although it is not visible until several weeks later. The infected area is seen as a small, 1/4- to 1/2-inch-diameter lesion next to or including part of the calyx. Usually brown, the spot is slightly sunken and often has a red border. A shallow, dry or corky rot develops in the flesh beneath the spot.

Blossom end rot appears to be more common in seasons of prolonged cool, wet weather during and shortly after bloom. It has appeared most frequently on Delicious, Rome Beauty, and McIntosh. On stored fruit, especially Delicious, blossom end rot often leads to moldy core.