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James R. Baker, Extension Entomologist Emeritus

CAUTION: This information was developed for North Carolina and may not apply to other areas.

Maple leaves frequently develop growths or swellings known as galls. Several types of these are caused by tiny mites, too small to be seen with the naked. eye. These galls are the result of an abnormal growth of the leaf tissue due to stimulation or "irritation" from the feeding of the mites. The mites pass the winter in roughened areas on the bark or in scars, wounds or other protected places. In early spring, the mites migrate to the buds and attack the young leaves. There are several generations of the mites during the summer, living and feeding inside the galls. In early summer, they migrate to the bark to spend the winter.

 Maple bladder gall mites cause more or less round swellings or galls on the upper surface of the leaves of silver maple. The galls are yellowish green at first but later become pinkish to red and finally black. There may be many galls on some trees or parts of trees and few on others. They may be very abundant one year and scarce the next.

 Maple spindle gall mites cause small spindle-shaped galls on the upper surface of the leaves of silver maple, sugar maple and whitebark maple. The galls cause no serious injury.

 Crimson erineum mites cause glossy, crimson, felt-like patches composed of numerous galled cells on the surface of maple leaves. These galls cause no serious injury to the foliage.

Drawing of maple bladder galls on maple leaf

Similar galls are common on boxelder, walnut and pecan as well as many other trees and shrubs. The presence of the galls disfigures and deforms the foliage. Also, when galls are very abundant, some leaves yellow and drop prematurely. In some cases, numerous galls have seemed to weaken branches or even whole trees. Ordinarily, however, mite galls cause very little harm and seldom are control efforts warranted.
These galls appear sporadically and do mostly cosmetic damage. The threat to the health of the tree is limited or negligible. Treatment is rarely justified. Because eriophyid gall mites crawl to the bark to spend the winter, trees could then be sprayed to suppress the mites there. By waiting until the leaves have fallen, it is easier to cover the bark thoroughly and much less pesticide will be needed. Following are some pesticides labeled for eriophyid mites or simply "mites" and may give some control if applied according to directions for safe use found on the label of the pesticide container. Some maples, such as some of the Norway maples, are much less susceptible to these mites. Though there are miticides listed, do not expect much control. It is easier and cheaper to just enjoy them.

Pesticide  (Trade Name)  Formulation
abamectin (Avid) Avid + hort oil
*carbaryl  (Sevin) wettable powder
*horticultural oil various apply just before bud break
*fluvalinate (Mavrik) 23% aquaeous flowable

* Suitable for home use.

Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
© 2001 NC Cooperative Extension Service
Prepared by: James R. Baker Extension Entomologist Emeritus

May 1994 (Revised)

Web page last reviewed January, 2011 by webperson.