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.

Damage:

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.

Life History:

Dogwood borers overwinter as immature larvae (caterpillars) in tunnels under the bark. Full-grown larvae are 25 mm (1 inch) long and white to cream in color with reddish-brown heads. Larvae change to pupae during spring and adults begin to emerge by early June.

Dogwood borer adult (left) and caterpillar. Photo by Dr. Jim Baker, North Carolina Extension Service

Adults are most abundant in July, though some emerge throughout the remainder of the summer months. Adults are clear-winged moths, active during daylight hours. They have blue-black bodies with a yellow stripe on the second and fourth segments of their abdomen; the legs also have yellow bands. The 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 the bark until an opening is found for their entry into the cambium; the larvae are unable to chew through bark. 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.

Control:

Cultural control:

The general prevalence of dogwood borers and the ease with which they penetrate injured bark makes control difficult. Preventative control measures include:

• Avoid physical injury to the tree by unnecessary cutting or bruising. Be careful in use of mowers near the base of trees.

• Brace newly transplanted trees to protect against strong winds.

• In some cases, wrapping the trunks of new trees will reduce egg-laying of female moths.

• Plant non-native dogwood varieties less susceptible to dogwood decline, since trees affected by this disease are more likely to be attacked by dogwood borers. See GreenShare Factsheet on Dogwood Diseases for more information.

• Maintain optimum growing conditions for trees and remove dead or cankered branches in dry weather.

Chemical Control:

Dogwood borers are difficult to control once the larvae have gained entry under the bark of a tree or branch. A residual insecticide applied in June may help reduce damage and reduce the number of adults which lay eggs on host trees, but coverage of trees is often expensive and difficult.

Adapted from the Delaware Cooperative Extension, 1999