Linden gall mite

You will notice small red to pink pimple-like growths erupting from the upper surfaces of linden leaves in June and July. These spindle galls, also called nail galls, measure about one-quarter inch long and may turn brown or yellowish as summer progresses. Puckered pits form on the corresponding leaf undersides. Three Tilia species in Puget Sound landscapes are affected by these microscopic mites.

This mite causes primarily cosmetic damage and rarely threatens tree health. No control is needed for most trees. If galls are objectionable, remove heavily infested leaves by hand during summer when galls are most visible. Mites overwinter in bark crevices and around buds, completing activity by late summer. Prune dead or declining branches to improve air circulation and reduce mite habitat.