Karen Rane, Plant Disease Diagnostician, Dept. of Botany & Plant Pathology, Purdue University
The dark blemishes on the skin of the apples in this photo are characteristic of the disease called sooty blotch. Sooty blotch is caused by several fungi that can infect apples in early stages of fruit development, colonizing the outermost layer of the fruit. Infected fruit do not decay or rot, but the superficial discoloration results in a loss of fruit quality. The disease is favored by high humidity and frequent rainfall during the growing season. In commercial orchards, management includes pruning trees to increase air circulation, and the application of fungicides. For more information on sooty blotch, see the following links:
Sooty Blotch and Flyspeck of Apple. Ohio State University Extension Fact Sheet HYG 3022-92
Sooty Blotch, Peltaster fructicola,Geastrumia polystigmatus, Leptodontium elatus, and Flyspeck, Zygophiala jamaicensis. West Virginia University Kearneysville Tree Fruit Research and Extension Center bulletin.
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