Both fungi overwinter on twigs of many wild hosts. Sooty blotch conidia are disseminated by wind into orchards from late May or June until fall. Here they infect fruit, twigs, andother parts of the tree. The fungus is active only in humid, cool weather. In late spring, with the approach of warm weather, growth is inhibited and sympotoms seldom appear.
Asthe temperatures cool in late summer, the fungus starts growing again.
The optimum conditions for its development are a temperature of 65 F. and a relative humidity of 80 to 95 percent. Under ideal conditions, the incupation period may be as short as 5 days. In the field, however, it is usually 20 to 28 days on fruits 42 to 45 days old. The life cycle of the fungus is little affected by the apple infections, since they do not produce conidia. However, condidia on the wild hosts cause new infections so that the pathogen is always present.