The dogwood borer, which occurs throughout the eastern United States, is probably the most destructive pest of established flowering dogwood trees. Young trees may die completely and older trees may be left with dead or dying branches. Damage by this insect severely limits the success and attractiveness of dogwood.
Borer-infested trees show swollen, knotty, calloused or gall-like areas on the trunk. Dogwood borer adults, which are clear-winged moths, make irregular burrows under the bark on the trunk, especially at ground level and around the base of limbs or at the edges of wounds or scars on the bark. Fresh sawdust-like borings are usually present on the bark near active borer sites. In young trees, the crown is attacked, resulting in wilting and die-back.
Annual Life Cycle
Dogwood borers overwinter as immature larvae (caterpillars) in tunnels under the bark. Full-grown larvae are 1 inch long and white to cream in color with reddish-brown heads. Larva change to pupa during spring and adults begin to emerge by late May. Adults are most abundant in June though some emerge throughout the remainder of the summer months.
Adults are clear-winged moths that are active during daylight hours. They have blue-black bodies with a yellow stripe on the second and fourth segments of their abdomen. Legs are also yellow banded. Wings are narrow and transparent.
Female moths lay eggs on smooth or rough bark. On older trees, they lay eggs in scars and rough areas of bark on the trunk and larger branches. Caterpillars hatch in 8 to 10 days and wander around aimlessly until an opening in the bark is found. These free-moving larvae are unable to chew their way through bark, so they seek an opening to gain entry to the cambium. Once inside, they are well protected and difficult to control. Larvae feed in this protected area throughout most of the year. One generation occurs each year.
(From North Carolina County Extension Service)