Cedar apple rust is an airborne fungus from eastern red cedar trees. The fungus releases from the cedar tree when the warm spring rains enlarge galls on the cedar tree limbs. The fungus can carry many miles from the host tree. The most effective method against cedar apple rust is to plant resistant strains of fruit trees. If trees are already established, the next-best method is to plan a maintenance schedule of fungicide applications during the early leaf and bloom formation on the affected fruit trees.
Consult your local agricultural extension service for its recommendations on fungicides for your area. The type of fungicide will depend heavily on the type of tree affected. While the actual apple rust fungus may be close to the same, the effect on various tree species may not.
Mix the approved fungicide according to the manufacturer's labeling instructions or the extension service's practices.
Apply the fungicide spray to every part of the tree that is being protected. Typically the application will take place in early spring while the young leaves and blooms are just beginning to emerge.
Use a second application if heavy rains have occurred. Generally after each rain, the possibility of cedar apple rust will be a concern until the leaves have fully emerged and the apples are greater than ¾ of an inch in diameter.
Inspect the tree leaves as often as possible. Look for signs of cedar apple rust on the leaves. The rust will show as small yellow spots on the young leaves. If this occurs, spray the tree as soon as possible with the fungicide.