I am fortunate to have many native flame azaleas growing on my property. But this time of year—April and May—just when they begin to bloom, I see abnormal growths at the tip of some stems. They look like little green apples and are slightly smaller than a ping pong ball. What are they?
Azalea Leaf Gall (Exobasidium vaccinii)
The growths are caused by a fungus that thickens the emerging foliage into these soft-tissue balls. The spores of the ripening fungus are spread by wind and splattering raindrops. They overwinter in the ground and on the plant’s branches and re-infect the azalea again in the spring. While the galls won’t kill the plant, they are unsightly. The best defense is to pick the galls while they are still small and green. Once they’ve turned white and begun to dry up, they release their spores and you’ll contend with even more galls next season. Exobasidium vaccinii primarily affects native azaleas, but it can spread to rhododendrons and hybrid azaleas, too.
Camellia Leaf Gall (Exobasidium camelliae)
I also have a beautiful stand of sasanqua camellias affected by leaf gall caused by a different fungus. The emerging leaves thicken and turn reddish. I check the shrubs every few days and clip off the affected leaves before the galls mature and release spores. Although Exobasidium camelliae mostly affects the sasanquas, other camellia species are also susceptible.
Be sure to sterilize your pruners between cuts so as not to spread the fungus to other branches. Dispose of the galls in a plastic bag and throw them in your trash—not the compost pile. Manual removal is usually the only treatment needed. Providing good air circulation minimizes the time rainwater stays on the leaves during rainy seasons, reducing the likelihood of fungal infections.
For more information about azalea leaf gall, view this publication from Cornell University: http://plantclinic.cornell.edu/factsheets/azaleagall.pdf
For more information about camellia leaf gall, check out this video from Clemson Cooperative Extension: http://www.clemson.edu/extension/hgic/videos_posters/videos/camellia_leaf_gall.html
Article written by Beth Leonard, Extension Master Gardener Volunteer.