Cedars can be towering beauties in lawns and forests. The trees have a fresh, evergreen scent and are popular in home landscaping. Apple trees have an all-American appeal as both landscaping and fruit trees. But these two specimens can be brought down by minuscule organisms like the fungus gymnosporangium juniperi-virginianae, better known as cedar-apple rust. This fungus jumps back and forth between apple and cedar trees, and can affect the foliage and even growth of the trees. If you think your cedar or apple tree is affected, take some immediate steps to prevent the rust from spreading.
Diagnose cedar-apple rust to make sure you're treating the right condition. In mid to late summer, orange spots will appear on the leaves of an apple tree, and even leaves that aren't affected may appear discolored or thin. In mid spring, orange growths or galls will appear on the trunk and roots of a cedar tree. These grow after the spring flowering and release spores of cedar-apple rust to the apple trees nearby.
Spray the surrounding trees with fungicide in mid-April, when galls are beginning to form on cedar trees. Because cedar-apple rust spreads by jumping back and forth between apple and cedar trees, preventing the jump will interrupt the life cycle of the fungus. Spray apple trees thoroughly with fungicide, including both trunk and foliage. Consider spraying the galls on the cedar as well.
Repeat the process every seven to 10 days, until the galls are finished spreading their spores and begin to fade.