Larger populations of the European red mite, Panonychus ulmi (Koch), developed on artificially infested young peach trees protected by screen windbreaks than on unprotected trees. In the laboratory rather high air velocities were required to blow mites off the leaves. Agitation of leaves without contact between them had no effect on the mites. Whipping of leaves back and forth caused appreciable mortality of mites on them, and mortality was further increased when the leaves could beat together. It was concluded that wind causes considerable mortality of mites in peach orchards mostly through friction between leaves.