Infected fruit become distorted and may crack, allowing entry of secondary organisms. Severely affected young fruit may drop. The pathogen overwinters primarily in infected leaves on the ground. New spores, referred to as secondary spores, are produced on the infected leaf or fruit surface 8 to 17 days later, allowing further spread of the disease in the tree until conditions become too hot and dry, or the plant tissue becomes more resistant to infection. Young infected flowers or fruit may drop or the fruit may become malformed and unsightly, rendering them unusable.
Defoliation follows severe early leaf infection.
In single backyard trees, removal of leaves from beneath trees in winter may be sufficient to limit the disease to tolerable levels. In plantings of several trees, additional steps may be needed to effectively control this disease, especially in cool, moist coastal areas. Cultural Control Rake and remove apple leaves from the yard in autumn or winter. Foliar applications of zinc and fertilizer-grade urea will hasten leaf fall in autumn. Either destroy or thoroughly compost the leaves.