Introduction to Sooty Blotch and Flyspeck of Apple
Sooty blotch and flyspeck are two distinct diseases, caused by different fungi. However, because both diseases usually occur together, and because their disease cycles and control procedures are similar, the two diseases are frequently "lumped" into a single disease complex.
Both fungi overwinter on the twigs and branches of many wild woody plants, in addition to apple. Spores are produced and blown or splashed onto fruit during rainy periods from May onwards; however, the diseases develop most rapidly during relatively cool, humid weather. Practically no fungal growth occurs at temperatures above 85 dgrees F; consequently, infections which are initiated in late spring may not become evident until the weather turns cool in the fall when fungi resume growth. Disease outbreaks are most likely to be severe when cool wet springs are coupled with summer rains and cool weather prior to harvest.
Sooty Botch Fruit Infection
Sooty blotch, as its name implies, appears as sooty brown or black blotches on the surface of nearly-mature apples (Figures 1 & 2). Blotches vary greatly in size, but may be 1/4" in diameter or larger. Several blotches may coalesce to cover relatively large areas of the fruit.
Flyspeck Fruit Infection
Flyspeck appears as a group of tiny, distinctly defined black dots, with several to 50 or more individual dots making up a single cluster. A number of different clusters may be found on a single fruit (Figures 1 to 2).
Figure 1. Sooty blotch and flyspeck on apple fruit
Figure 2. Close-up of sooty blotch and flyspeck
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