sooty blotch and flyspeck fungi live on the waxy layer that coats
the surface of apple fruits. The fungi include: Zygophiala jamaicensis,
the causal agent of flyspeck; and three sooty blotch fungi, P.
fructicola, Leptodontium elatius, and Geastrumia polystigmatis.
fungi live on sugars and other nutrients that leak out of the apple.
They also survive and grow on the twigs and branches of many woody
plants, including apple, but are especially likely to occur on raspberry
and blackberry canes. Spores released in the late spring and summer
spread to apple fruits by rain and wind. In the Upper Midwest, the
first symptoms of sooty blotch and flyspeck typically appear in late
August to early September, but can appear earlier in wet years. On
the other hand, sooty blotch and flyspeck symptoms can be rare or
even absent in Upper Midwest orchards in years when rainfall is sparse.
blotch and flyspeck tend to be more visible on light-skinned (yellow
or green) than on red apple cultivars, and more severe on late-maturing
than early-maturing cultivars.
for pictures of the infected apple.