Disease Facts Cooperative Extension - The Pennsylvania State University Azalea Leaf Gall Gary W. Moorman Plant Pathologist Young leaf and flower tissue of azalea is susceptible to infection by the fungus Exobasidium vaccinii in the spring. Infected tissues become swollen, fleshy, and curled. The gall is white, pink, or pale green at first, but later becomes brown and hard. Other plants susceptible to this fungus include rhododendron, arbutus, blueberry, camellia, and leucothoe.
Plants growing in shady areas where the humidity is often very high are most susceptible.
After that time, tissues are no longer susceptible. The fungus forms a coating of white spores on the surface of the gall. These spores are dispersed by the wind but remain dormant on the plant until the following spring. Thus, the fungus has one period of infection in the spring and does not continue to cause more disease during that same year. Avoid establishing dense plantings of susceptible species.