I have had a call recently about Azalea Leaf Gall. It seems to be more common this time of year due to favorable weather conditions. Below is information from UGA’s Ornamental Extension Plant Pathologist Dr. Jean Williams-Woodward
Camellia leaf gall, caused by the fungus Exobasidium camelliae, occurs more frequently on sasanqua than japonica camellias. A similar leaf gall caused by a related Exobasidium species occurs on azaleas, mountain laurel, and other Ericaceous plants. Leaf and flower galls cause little damage to the overall health of shrubs or to camellia flowering but may be unsightly in the landscape planting. Severity of the disease varies according to the weather conditions when leaf expansion begins in the spring. Cool, moist weather favors disease development. The disease is rarely seen under dry weather conditions, but frequent overhead sprinkler irrigation can provide the moisture necessary for disease development.
The lifecycle of camellia (and azalea) leaf gall is poorly understood. Since it is more of an aesthetic problem, there has been little research into figuring it out. It is thought that the fungus survives during the winter in leaf buds and infects the expanding leaf tissue in the spring. Instead of developing normally, the new leaves become thickened and succulent and may be larger than normal (see attached images). The diseased leaves are a light green to pinkish-green color. Eventually, the epidermis on the underside of the camellia leaf peels away and exposes a white surface. On azalea galls, the whole galled leaf or flower turns white. Spores are released from the white surface and are dispersed by air currents and splashing water. The galled leaves will dry and turn brown to black in late spring.
Control is primarily achieved by removing and discarding the galled leaves and/or flowers as soon as symptoms are seen and before the surfaces turn white and spores are liberated. Fungicide applications are seldom necessary and provide only limited disease control. If warranted, fungicides containing pyraclostrobin + boscalid (Pageant), pyraclostrobin + triadimefon (Trigo, Armada), chlorothalonil (Daconil. etc.), or mancozeb (Dithane, Fore, etc.) need to be applied preventively as the leaf buds swell in the spring. Spraying after infection occurs and disease symptoms are present has no effect on controlling the disease during the growing season. I generally don’t recommend fungicides because it is likely to be ineffective.
Below Azalea Leaf Gall photo 1 & 2. Camellia Leaf Gall Photo 3 & 4.
