We have been receiving inquiries regarding oak spider mite, Oligonychus bicolor. This is a small (0.5 mm-long), dark, reddish brown mite that primarily attacks oaks (Quercus spp.) but can also be found on birch, beech, elm, and hickory. The mites are primarily located along the midrib on the lower leaves of large oak trees. Oak spider mites have styletlike mouthparts, which they use to withdraw plant fluids, creating scattered chlorotic stippling on leaves. Leaves turn yellow or have a bronzed appearance before eventually dying. Heavy infestations of oak spider mite can cause severe leaf bronzing. Red, barrel-shaped eggs are present on the upper surface of leaves. The eggs, which are the overwintering stage of oak spider mite, are laid summer through fall in crevices and around the leaf axils.
Oak spider mite can be managed by thoroughly spraying trees with a hard water spray. This dislodges all life stages, including eggs. Localized infestations can be pruned out. Insecticides/miticides recommended for controlling oak spider mite include insecticidal soap, horticultural oil, abamectin (Avid), bifenthrin (Talstar), and hexythiazox (Hexygon). Hexygon is an ovicide that kills mite eggs and young nymphs but does not have activity on adults.