Cedar Apple Rust (Gymnosporangium juniperi-virginianae Schwein.)

The fungus reaches the cedar by way of airborne spores produced by the fungus during the summer while in its apple host phase. Spores that successfully colonize the cedar will form a small, hard nodule on the new cedar leaves. The nodule, called a gall, will grow in size until it matures approximately 18 months later. When spring rains and temperatures produce the proper conditions, filaments called telia emerge from dimple-like structures on the gall’s surface. Fully hydrated telia produce the spores that will be released to colonize an apple tree. Spores produced by galls on the cedar cannot establish themselves on cedar. They can only colonize on apple, and spores from the apple can only colonize cedar. In order for the fungus to survive, both apple and cedar must be present in the vicinity.