Azalea gall disease may severely affect the aesthetics of your home garden. A specific fungal pathogen infects azaleas as well as other host plants and results in the unsightly formation of galls. Familiarize yourself with what to look for and effective control methods for vigorous azalea plants in your home landscape.
Azaleas that are kept vigorous through proper care are more likely to escape gall disease than those in a weakened state. Grow your azaleas in a location that provides partial shade like areas beneath a tree canopy. Full sun exposure may cause flower development problems or lead to insect infestations. Azaleas prefer extremely well-drained acid soil high in organic content with a pH of 4.5 to 6.0, according to the Clemson University Extension.
Azalea gall disease is caused by the fungus Exobasidium vaccinii during the spring season, according to the Alabama Cooperative Extension System. Sporadically spread by wind and rain, white- or pink-hued spores land on azaleas and infect leaves, flower buds and shoots. Germination and further development of the fungi are promoted by high moisture content and cool temperatures.
Swollen, soft areas of plant tissue called galls form on infection sites in the site-specific color. Shoot and leaf galls are usually green while flower bud galls appear the same color as the blossom, according to the Alabama Cooperative Extension System. Galls may be tiny or grow to a size exceeding 1 inch in diameter. As the disease progresses into summer, galls dry up, become brown and drop from the azalea plant. Azaleas appear deformed and experience diminished vigor.
Susceptible and Resistant Azaleas
To avoid azalea gall disease, stay away from susceptible cultivars and choose to plant resistant ones instead. Though resistant cultivars are not immune to gall disease, their likelihood of infection is much lower. Susceptible cultivars include, but are not limited to, Copperman, Herbert and Mother's Day. Resistant cultivars are Aphrodite, Formosa, Gloria, New White and White Jade, according to the Alabama Cooperative Extension System.
For control of azalea gall disease, remove and destroy infected plant parts. Sanitize your pruning tools between cuts and particularly from one azalea to the next to prevent spreading fungal disease. Don't crowd plants, but provide adequate circulation to keep moisture levels to a minimum. For a chemical control option, use preventive fungicides to keep galls from forming; the fungicide Bordeaux applied right before bud break and applied one more time approximately three weeks later is an effective method, according to the Alabama Cooperative Extension System.