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.
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. Because eriophyid gall mites crawl to the bark to spend the winter, trees can then be sprayed to control the mites there.