Azalea leaf and flower gall is a disease that causes concern to many Virginia home gardeners each year. It is caused by the fungus Exobasidium vaccinii. In home landscape plantings, the disease is more alarming than damaging, but in greenhouse plants grown under very humid conditions, galls may become so abundant that they cause considerable harm if control measures are not implemented. Closely related species of Exobasidium cause similar galls on other plants, including species of Arbutus, blueberry, Camellia, Ledum, Leucothoe and rhododendron.
Exobasidium vaccinii causes leaves and flowers to become swollen, curled, waxy and fleshy (Fig. 1). The swollen plant tissues or "galls" are made up of abnormal plant tissue. Infected leaf tissue is usually pale green in color during the early stages of the disease; infected flowers are usually pinkish. Later in the season, a white spore layer covers the infected plant parts. Galls eventually turn brown and harden as the season progresses. Lower leaves on plants are usually the most seriously damaged, but under humid conditions and in shaded locations galls may occur at the ends of upper branches.
Some azalea cultivars with resistance to leaf and flower gall have been reported. Resistant and susceptible cultivars of azalea are listed in Table 1. The Purple Splendor and Roseum cultivars of rhododendron are also highly susceptible to this disease.
Cultivars of azalea exhibiting resistance or susceptibility to azalea leaf and flower gall
|Highly Susceptible Azalea Cultivars|
|China Seas||Hinodeii||White Gumpo|
|Resistant Azalea Cultivars|
|Eikan||Mrs. G. G. Gerbing||Sunglow|
|Formosa||New White||White Jade|
|Glacier||Pride of Summerville|
Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does not endorse these products and does not intend discrimination against other products which also may be suitable.
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Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Alan L. Grant, Dean, College of Agriculture and Life Sciences; Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Jewel E. Hairston, Administrator, 1890 Extension Program, Virginia State, Petersburg.
May 1, 2009