Problem: Cedar-Apple Rust (Apple)
This plant disease is caused by a fungus (Gymnosporangium juniperi-virginianae) that affects both apples and certain species of juniper and red cedar. This fungus cannot spread from apple to apple, or from juniper to juniper, but must alternate between the two. In the spring, spores from brown and orange galls on juniper or cedar are blown up to 3 miles to apple trees. During mild, wet weather, the spores germinate and infect the leaves and fruit, causing spotting and, eventually, premature leaf and apple drop. During the summer, spores are produced in the small cups on the undersides of leaves. These spores are blown back to junipers and cedars, causing new infections and starting the cycle again.
This fungus can only spread between cedar, juniper, and apple trees. Cedar-apple rust cannot be controlled on the current season''s apples and leaves. The following spring, spray apple trees with a fungicide when the flower buds turn pink, again when most of the petals have fallen from the blossoms, and once more 10 days later. When practical, do not plant apples within several hundred yards of junipers or red cedar.