Now is the time of year to be on the look out for the peachtree borer, Synanthedon exitiosa. Peachtree borer attacks the base of trees in the genus Prunus, including purpleleaf plum, flowering cherry, and wild-black cherry, as well as peach, apricot, plum, nectarine, and cherry. Damage generally appears as a mass of gummy sap and brown frass, called gummosis, at the base of the trunk. The bark may also slough off in large pieces from the trunk near or at ground level.|
Adult moths resemble wasps. The males have slender, bluish black bodies with narrow yellow rings and clear wings. Female moths also have bluish black bodies but possess 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 are active during the day, and they resemble wasps when in flight. Females are attracted to and tend to lay eggs on trees previously infested with borers or trees that have been wounded. Peachtree borer females lay eggs on the trunks of trees or in crevices in the soil. They can lay between 200 and 700 eggs over a comparably extended time period, which means that the developmental period of the larval instars may overlap. The eggs hatch into larvae that feed in the cambium area just under the bark, from 2 to 3 inches below ground to 10 inches above ground. The larvae are 1/8 to 1/2 inch long, yellow–white, robust in shape, and legless, with a brown head. Full-grown larvae are about 1 inch long. They feed throughout the summer and early fall, pupate in spring in the soil near the base of the tree, and then emerge as adult moths in spring. The peach-tree borer overwinters as larvae, and there is one generation per year.
Peachtree borer primarily attacks recently planted young trees that are adapting to a new site, as well as mature or unhealthy trees. Trees in the genus Prunus are not long-lived, depending on the species. In particular, purpleleaf plum and flowering cherry may not live much more than 10 to 20 years in northern Illinois. However, the tree has a longer lifespan in the southern regions of the state. Local site conditions can stress trees, futher shortening life spans.
Applying the insecticide permethrin (Astro) to the lower trunk and base of trees when mock orange (Philadelphus coronarius) is in bloom should reduce potential borer infestation. Treatments are made sooner in southern Illinois than in central and northern Illinois. Pheromone traps are very helpful in accurately timing treatments. The traps are effective in trapping the males, although the pheromone also attracts other clear-winged male moths, such as dogwood borer, lilac/ash borer, and viburnum borers. Treatment is generally recommended about 2 weeks after the peak male moth catch.