Apple scab is of major economic importance in the mid-Atlantic region.
Losses result directly from fruit or pedicel infections, or indirectly from repeated defoliation which can reduce tree growth and yield. Apple scab can be observed on leaves, petioles, blossoms, sepals, fruit, pedicels, and less frequently, on young shoots and bud scales. The first lesions are often found on the lower surfaces of leaves as they emerge and are exposed to infection in the spring. L ater, as the leaves unfold, both surfaces are exposed and can become infected. With time, the margins become distinct, but they may be obscured if several lesions coalesce.