Sooty Blotch and Flyspeck on Apple
Gail Ruhl, Senior Plant Disease Diagnostician, Purdue Plant and Pest Diagnostic Lab
The dark blemishes on the skin of the apple in this photo are characteristic of a disease complex caused by a number of different fungal species. The diseases are named after their appearance – sooty blotch and flyspeck. Sooty blotch is characterized by the sooty smudges on mature fruit while flyspeck appears as clusters of sharply defined, black, shiny specks on the fruit surface. Fruit infection can occur anytime after petal fall but is most prevalent in mid-to-late summer during periods of high humidity and frequent rainfall. All varieties, including scab resistant varieties are susceptible to sooty blotch and fly speck, but symptoms are more apparent on yellow, green or light colored fruit. Infected fruit do not decay or rot, but the superficial discoloration results in a loss of fruit quality. Proper care, including pruning to increase air circulation and shorten drying time of fruits and foliage can reduce problems with sooty blotch and fly speck but high quality fruit may require the use of fungicides (see Managing Pests in Home Fruit Plantings – ID-146-W). Alternatively home gardeners may choose to lightly scrub the apples with a cloth to reduce traces of the disease.
More information can be found here: Sooty Blotch and Flyspeck of Apple. Ohio State University Extension Fact Sheet HYG 3022-92 (pdf file).