Cottonwood (Populus)-Carpenterworm

Prionoxystus robiniae

Pest description and damage Carpenterworms are the larvae of a large mottled gray and black moth. The caterpillars are greenish-white to pinkish with a dark head and are 1 to 3 inches long when mature. The caterpillars bore in the trunk and main branches of cottonwood, ash, birch, black locust, poplar, willow, elm, oak, locust, maple, pear and other deciduous trees and shrubs. Discolored or bleeding limbs, branch dieback, and lumpy or gnarled trunks may be indications of carpenterworm infestation.

Biology and life history Adults emerge in late spring and early summer and begin laying eggs. Females lay between 200 to 1000 olive brown eggs during her life, mostly in groups of 2 to 6 eggs. Eggs are found in sticky masses in cracks and crevices of the bark of host plants. After hatching, the larvae bore into the sapwood where they tunnel and feed for up to two to four years before they are mature.

Management-cultural control

Keep trees vigorous, as healthy trees are better able to tolerate some damage. Prevent injuries that attract carpenterworm moths to trees. Poke a wire into tunnels to kill larvae. Prune trees in late fall and winter so that moths are not attracted to fresh wounds. Remove infested branches.

Management-biological control

Apply beneficial nematodes (Steinernema carpocapsae or S. feltiae) into tunnels to kill larvae. Fill tunnels with nematodes in water, then plug holes and wait about a week. It may be necessary to treat tunnels again if plugged holes are reopened by surviving larvae. Natural enemies recorded for this pest include downy woodpeckers, ichneumonid wasps, and fungi.

Management-chemical control

See Table 4 in: