Galls are unattractive raised bumps on a plant or tree's leaves. These brown, gray, green or white lumps can be nasty looking, but most are not harmful. In fact, the majority of leaf galls arise as a reaction of plant tissue to the activity of insects feeding on the leaves. Leaf gall on azaleas, though, is not harmless. The disease arises from a fungal infection, and not only deforms the leaves, but limits the plant's ability to flower. If left untreated, the fungus can quickly spread to other azaleas.
Remove infected leaves as soon as they appear. The leaves will thicken and twist, and then they will become covered with a white powder, which is the spores of the fungus. Slip on protective gloves and simply pluck off the infected leaves.
Prune away any heavily infected branches. Since the fungus appears in the spring, this will not stunt the growth of the plant.
Place the infected leaves and branches into a trash bag rather than letting them drop onto the ground, as the fungus can move from the leaves to the soil. Once in the soil, it can overwinter and appear again on the azalea in the spring.
Treat the azalea with the Bayleton fungicide. Repeat the application every two weeks. For best results, begin spraying as soon as you notice infected leaves.
Remove any old mulch from under infected azalea plants and replace it with new mulch, as there could be fungus in the old mulch.