Black oak, Quercus velutina Lamarck, is the dominant deciduous tree on Cape Cod, Nantucket, and Martha's Vineyard, Massachusetts, and in recent years it has experienced widespread mortality and severe canopy loss due to infestations of a stem gall wasp, Zapatella davisae Buffington and Melika (Hymenoptera: Cynipidae). A single application of systemic insecticides emamectin benzoate and imidacloprid was found to reduce or prevent further accumulation of Z. davisae damage on infested black oak during a 1-yr trial.