The disease spreads from the cedar to the apple and then back to the cedar. It can be a severe problem wherever these two are grown together, and most ornamental crabapples and apples are susceptible. This disease has raised spots on leaves that are bright orange-yellow. Leaves and fruit can drop from the tree. Severe defoliation can lead to reduced bloom the next season.
Spots develop primarily on the leaves in mid- to late spring.
Infected fruit is often small and distorted. On the Eastern red cedar, hard brown galls up to 2-inches in diameter form near the ends of branches in the summer. In the spring following a rain, the galls produce large, orange, gelatin-like tendrils, full of spores, which can blow up to a mile to infect nearby apple or crabapple trees. If possible, remove red cedars from the area or prune out galls on nearby cedars. If disease is severe enough to warrant chemical control, select from the chemicals below.