Scab (fungus - Venturia inaequalis): This fungus attacks both the foliage and the fruit. It first appears on the leaves as small, dull, smoky areas which with age become olive colored, velvety, and much more visible. On fruit, the lesions are first small, circular, olive green areas which turn dark and scabby. The spots crack open in late stages of development.

The fungus overwinters in fallen apple leaves. The fungus produces fruiting structures in the spring. Rains cause spores to be shot into the air where they are carried to developing foliage. The spore will germinate and produce a leaf spot if moisture is present when the spore lands on the leaf. Further spread occurs from these spots to adjoining leaves of fruit. Apple scab is dependent on moisture for development.

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