Sooty blotch is a disease complex and is caused by several unrelated fungi. Flyspeck is caused by the fungus Zygophiala jamaicensis. These blotches can be removed by rubbing vigorously and are olive-green to black. Both fungi overwinter on the twigs of many woody plants as well as apple and pear. Spores of the fungi are windblown and rain splashed onto fruit.
Infection can occur anytime after petal fall but is most prevalent in mid-to late summer.
Disease outbreaks are favored by extended periods of above normal summer temperatures combined with frequent rainfall and high humidity. These diseases usually appear on fruit late in the season. Cultural controls include the removal of alternate hosts such as wild blackberries from the orchard and surrounding hedgerows. Dormant and summer pruning that opens up the tree canopy and facilitates air movement and the drying of fruit after a rain period will help in the control of these diseases. Thinning to separate the fruit clusters will also help prevent sooty blotch and flyspeck.