Pest Alert: Azalea Leaf Gall

Azalea leaf gall

   The warm, wet spring has been ideal conditions for leaf gall in azaleas. Leaf gall is a common fungal disease found on azaleas.  The  leaf gall of azaleas is caused by the fungus, Exobasidum yaccinii. Another fungus, Exobasidium camelliae, causes a similar problem in camellias. It occurs more commonly on the fall blooming ‘sasanqua’ varieties.

   This disease appears early in the spring. The new leaves and buds that are infected develop distorted growth. The leaves become thickened, curled, and pale green to white and in some cases pink. Leaves can be ten times thicker than normal leaves. The infected  leaves are covered with a white powdery substance in the latter stages of the disease. Galls eventually turn brown and harden as the season progresses.

   Fundal spores overwinter in the bark. When the buds open in the spring, the spores are blown by the wind to the plant. Rain can also wash spores from the bark to the plant tissue. Spores need moisture to germinate. Plants that are grown in areas of poor air movement, deep shade, and high humidity are more likely to be infected.   After the plant is infected, the fungus stimulates a growth promoting process which causes the thickening and distortion of the plant.

   There are some varietal differences among azaleas in susceptibility.  Reported resistant varieties include: Gloria, Sensation, Coral Bells, Mrs. G. G. Gerbing, Sunglow,  and Formosa.

   The disease usually does not do enough damage to require chemical control. If only a few plants are affected, prune the galls of the plant and throw them in the trash.  If the same plants get infected year after year then might be chemical control necessary.   Begin treat with captan, mancozeb, or triadimefon fungicide sprays starting wien the young leaves begin to unfurl then every 10 14 days after that until the young leaves mature. 

    Another procedure for controlling azalea leaf gall on badly diseased plants is to cut plants back severely. This is a good sanitation procedure and is a good way to reduce disease occurrence  the following season because galls will be removed along with the pruned branches. It is also advisable to replace mulch beneath such plants since this will insure that fallen galls beneath plants will be removed.