Peachtree borer, Synanthedon exitiosa, attacks the bases of trees in the genus Prunus, which includes purple-leaf plum, flowering cherry, and wild black cherry, as well as peach, apricot, plum, nectarine, and cherry. Damage will appear as masses of gummy sap and brown frass called gummosis at the base of the trunk. The bark may also slough off of large areas of the trunk near ground level.

Peachtree borer larvae feed in the cambium area just under the bark from 2 to 3 inches below ground to 10 inches above ground. The larvae are yellow—white, full-bodied, and legless, with brown heads. Full-grown larvae are about 1 inch long. They feed through the summer, pupating in the spring in the soil near the base of the tree. Adult moths emerge in the spring.

Adult moths are wasp mimics. Males have slender bluish black bodies with narrow yellow rings and clear wings. Female moths also have bluish black bodies but have a broad orange band halfway down the abdomen. The female’s wings are opaque, with bluish black scales; however, half of the hindwings are transparent. Both sexes fly during the day; in flight and in walking, they are similar to wasps.

These insects primarily attack young trees adapting to site as well as overmature, declining trees. Trees in the genus Prunus are not long-lived, depending on the species. In particular, purple-leaf plum and flowering cherry may not live much more than 10 to 20 years in northern Illinois, with somewhat longer life spans as one goes farther south. Local site conditions can stress trees, shortening life spans further. Peachtree borer, along with cankers and other insects and diseases, are likely to attack a declining tree. The landscaper should decide whether it is in the client's interest to replace the tree rather than treat it, based on the age of the tree, growing conditions, and other factors.

For landscape trees, application of permethrin to the lower trunk and base of the tree when mock orange is in bloom should be effective. Treatment should occur now in southern Illinois and soon in central and northern Illinois. Pheromone traps are very accurate in determining treatment times. They are effective in trapping the males, although the pheromone will also attract other male clear-winged moths, such as dogwood borer, viburnum borers, and lilac borer. Treatment is recommended about 2 weeks after the peak of male moth catch.