I have received many calls in the past few weeks from homeowners concerned with their azalea and camellia bushes. Most notice swollen, disfigured leaves towards the growth tips of their shrubs. This disease is called leaf gall, caused by a fungal agent, Exobasidium, and occurs frequently during springtime.
Symptoms of an Exobasidium gall infection include the presence of thick, fleshy leaves, as well as thickening of the young shoots. Leaves infected with this fungus will often change colors, ranging from cream to red to light green.
The galls mature as spring progresses and the lower leaf surface will peel away, revealing a white layer that contains the spores of the fungus. These spores can then be blown by the wind to other susceptible plants. These spores will infect new plants and lay dormant until the beginning of next spring.
Management of this unsightly disease is relatively simple. Most galls can be picked off by hand or pruned off with hand pruners. Hopefully, you can remove them before the fungal spores are exposed to prevent further spread.
Make sure to burn or throw away removed galls. If you were to discard them somewhere else in your yard or compost pile, the spores will most likely survive and continue to spread. Make sure to clean the blades of your hand pruners with a solution of either alcohol or bleach. This will prevent fungal material from transferring to other plants.
If you have plants where serious leaf gall infections happen yearly, you do have some fungicide options for large-scale control. Fungicides with the active ingredient of chlorothalonil and mancozeb are effective in controlling leaf gall fungus. However, these must be sprayed very early in the spring, coinciding with leaf emergence. Plan on doing this next year for fungus control.
The good news about azalea and camellia leaf galls is that the disease is not one that normally threatens the long-term health of plants. The wet conditions of early spring so far have made it a great growing environment for the fungus. The conditions best for this disease will soon be gone. But, since this disease is mostly an aesthetic issue, the survival of most azaleas and camellias is not in jeopardy.
County Extension Agent