Apple Disease - Blossom End Rot

Blossom end rot of apple, is caused by various fungi (Sclerotinia sclerotiorum, Botrytis cinerea, Botrysphaeria obtusa) just before or during petal fall.
Apple Disease - Blossom End Rot - Articles


Source: Mary Ann Hansen, Virginia Polytechnic Institute and State University,

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 infected area is seen as a small, 14- to ½-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. It is often referred to as "dry eye rot" or "calyx end rot."

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. Captan and Topsin M have shown efficacy; however, the efficacy of other fungicides is unknown. This disease is typically sporadic and losses are minimal.