The Q&A Archives: Azalea Leaf Gall

Question: For several years galls have been developing on some of my deciduous azaleas (in the spring). It is either flower gall or leaf gall. Maybe flower gall. Some cultivars seem to be resistant while some always display the galls. Is there a fungicide I should use? Up to now, I have been picking and disposing of the galls but I would rather spray if I knew the best fungicide and the correct timing. Thank you.

Answer: Actually, what you are already doing is a good control measure. By practicing good garden sanitation, you'll go a long way in stopping the spread of the fungus. However, there are some azaleas that are more susceptible to the problem and you may be growing those.

Here's the background on Azalea Leaf Gall:
In early spring, small, soft, swollen areas form on leaves, flower buds, and sometimes on new shoots. Typically, the developing leaf and shoot galls are green while blossom galls are the color of the normal blossoms. Galls can be small, or they can develop into swellings an inch or more in diameter. Whole leaves or parts of leaves may become galled. As azalea galls age, their surfaces become white with masses of spores. Later on in the spring or early summer, old galls turn brown, shrivel, and fall to the ground.

The white or pinkish spores produced on galled tissues or on lower surfaces are spread by wind and splashing rain to nearby healthy leaves, shoots, or buds. Initial infections occur when the spores contact susceptible tissues. Galls form the following spring. Cool, moist weather favors spore development, dispersal, and infection. The disease is often more severe in shaded areas with high humidity.

Cultural methods provide the most practical control for azalea gall in most home landscapes:

Hand remove and discard all galled leaves and yellow or white spotted leaves on rhododendrons before they become white or pink with spores.

Destroy galls. You can add galled leaves to a hot, properly maintained compost pile.

Prune overhanging branches to improve air circulation and sunlight penetration.

Allow adequate space between plants. Prune to keep the landscape open to decrease humidity levels.

Do not plant extremely susceptible azalea cultivars such as China Seas, Copperman, Herbert, Hinodegiri, Mother's Day, Rosebud, or White Gumpo. The rhododendron cultivars Purple Splendour and Roseum are also especially susceptible to leaf gall.

If possible, plant a leaf gall resistant cultivar such as Amoena, Aphrodite, Coral Bells, Eikan, Faker, Formosa, Glacier, Gloria, Hampton Beauty, Kow-Ko-Ku, Mrs. G. G. Gerbing, Nancy, New White, Pride of Summerville, R. Poukhanese, Sensation, Thinbegen, Sunglow, Treasure, or White Jade.

Place susceptible varieties in locations where they will get maximum exposure to sun and air movement.

Use protective fungicide spray applications to give some control of leaf gall. Apply Bordeaux mixture or Bayleton just before bud break; apply a second time 2 to 3 weeks later. Follow specific label directions. Add a spreader-sticker to Bayleton to allow for complete spraying coverage.

Be sure to use chemicals only according to the directions on the label. Follow all directions, precautions, and restrictions that are listed.

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