Sooty blotch and flyspeck are caused by two different fungi that usually occur together on the same fruit. Sooty blotch appears as superficial, dull black spots or blotches that may merge to cover most of an apple. Flyspeck appears as clusters of 6 to 50 or more slightly raised, black shiny round dots that resemble fly excreta.
Because the fungi that cause sooty blotch and flyspeck grow superficially on the surface of the fruit, losses are primarily through lowered quality. (The black discoloration can be removed by vigorous rubbing.)
Several cultural practices aid in the control of sooty blotch and flyspeck, although control is based primarily on the use of protectant fungicide sprays. Pruning, which facilitates drying, has been shown to reduce disease incidence and severity. The value of pruning, however, is somewhat dependent on the season. It appears to help more in dry seasons than wet seasons. Proper thinning of fruit is also helpful.
Pm-673 "Recognizing Common Apple Diseases in Iowa" has information and color photos of sooty blotch and flyspeck. Also refer to Pm-175 "Home Fruit Insect and Disease Management" for further control information.
This article originally appeared in the October 13, 1995 issue, p. 139.