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Updated: September 28, 2017
The disease, caused primarily by the fungus Botrytis cinerea, attacks the blossom end of apple fruit. The infection is likely to occur during bloom, although it is not visible until several weeks later. The infected area appears 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 dry or corky shallow 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, McIntosh, and Rome Beauty, apples. On stored fruit, especially Delicious, blossom end rot often leads to a moldy core.
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