It will attack a wide range of apple varieties. It has not been found on the western slope in the commercial apples and, because of the desert-like climate there, may not develop in that important commercial orchard area. Apple scab is a moisture- enhanced disease and leaves must be wet for infection to take place. The fungus can attack leaves, petioles, blossoms, and fruit. So far, we have seen symptoms on the leaves.
Infections develop first on the lower side of leaves only.
Both sides of the leaf will eventually be infected. Severe infections will cause defoliation. Leaf spots develop as brown fuzzy to olive-colored spots which turn black with age. The margins of the spots will initially be indefinite and even a little feathery. Later, the margins will become very distinct.