In the early spring the adults move to the developing, unfolding leaves and begin feeding. The leaf responds to the small irritation by rapidly producing extra cells that form the abnormal growth at the feeding site. The gall encloses the mite which continues to feed and lay numerous eggs within the gall. Reproduction is prolific and as the new mites mature, they leave the gall and move to other newly emerging leaves to repeat the process. Only new leaves are capable of producing galls.
Mite activity continues until mid-summer when it starts to decline.
Adult mites leave the foliage in the fall and move to the overwintering sites. Heavy infestations of galls cause leaves to be disfigured. At the worst, leaves become curled or rolled up, and may change color and drop prematurely. These effects are not detrimental to the overall health of healthy, well-established trees. The galls are unsightly and may appear to be severe, but the effect on the tree is not significant.