Billions of spores can be produced on a single spore horn. Release of spores occurs during rainy periods. In Connecticut, spores are released until about the middle of June. If a spore lands on a susceptible apple leaf and environmental conditions are favorable, infection can occur in as little as four hours. In one to three weeks, rust lesions appear on the apple leaves.
Spores produced in aecia on apple leaves are wind disseminated back to leaves of Juniperus spp.
The spores germinate, penetrate the leaves and cause galls. The galls produce spores the second spring after infection occurs, completing the two-year life cycle of the fungus. Control Removal of Juniperus spp. Since spores produced on the cedars can be wind disseminated several miles, tree removal cannot be expected to give complete control. However, removing Juniperus spp.