Landscape - Oak Problems Related to Insects

The following are some common insect related problems in oaks.

OAK SKELETONIZER. This native insect has two generations per year in our area and is active from 547 2846 GDD. The second generation occurs sometime during late July to August. The larvae are yellowish green and prefer to eat red oaks, but also feed on chestnuts and other oak trees. Early instars feed as leaf miners, but older larvae feed externally and skeletonize the leaf. Mature larvae drop from leaves on silken threads when disturbed. Populations vary by year, thus some years damage may not be noticed. Severe infestations or repeated attacks by this insect can result in crown thinning, die back, and possibly increase the trees susceptibility to other pests such as borers. Larvae form white ribbed cocoons on the leaves, twigs, or other nearby structures. Control options include B.t., bifenthrin, deltamethrin, cyfluthrin, or cyhalothrin.

Oak Skeletonizer. Photo by James Solomon, USDA Forest Service, Bugwood.org

OAK LACE BUG. This insect is very similar to lace bugs found on azaleas, hawthorns, and sycamores. Their fall peak of activity is between 1613 3384 [2300 peak] GDD. Stipled leaves have black 'tar spots' on the underside of the leaf. There are two generations per year in our area. Natural enemies often keep this insect controlled, however when treatments are necessary options include acephate, carbaryl, pyrethroids, or imidacloprid. Horticultural oil or insecticidal soap are options when temperature and humidity permit.

Oak lace bug. Photo from USDA Forest Service - Northeastern Area Archive, USDA Forest Service, Bugwood.org

OAK GALLS. Many different types of galls are found on oaks. These galls generally do not harm the health of the tree. Stem or twig galls such as the horned oak gall may be found on pin, scrub, black, blackjack or water oaks. Another stem gall, gouty oak gall, occurs on scarlet, red, pin, or black oaks. The wasps inside these galls often take a couple years to develop and are protected from insecticide applications; therefore an effective control option is to prune out the galls to lower populations. Collect and destroy fallen leaves to reduce populations.

Horned oak gall. Photo from USDA Forest Service - Northeastern Area Archive, USDA Forest Service, Bugwood.org

Brian Kunkel, Ornamental IPM Specialist, UD