Tree borers are the larval stage of different moths, beetles and occasionally, flies and wasps. Though the adults are different, all larvae incur similar damage as trees, as they eat and tunnel their way into the sapwood of a tree under the bark. Not only does the aesthetic and structural quality of the infected tree suffer, but the infection also lowers the economic value of lumbar. Tree borers are discouraged from trees in a variety of ways that include preventative measures.
Monitor the trees regularly for signs of infestation to control pest populations early. Having knowledge of the potential borer species helps with the choice of pesticides. Large numbers of very small holes in bark are usually the sign of bark beetles. Open tunnels filled with sawdust-like material are caused by clearwing moths. Dark wet sites on bark with D- or O-shaped holes are the work of roundheaded or flatheaded borers.
A large number of borers are classified as secondary pests that infest trees that are already under some form of stress or suffering from disease. Keeping trees healthy is a critical line of defense against borers, as there is no cure for serious infestations. Use tree varieties that are well suited to local growing conditions. Maintain tree health with adequate water and fertilizer. Do not prune between late winter to late summer, as this is when most borers adults are in flight. Avoid unnecessary damage to roots and trunk.
In cases of lighter infestations where damage is localized on branches, prune and remove infested areas. Use a stiff wire to insert into holes on the bark to kill the larvae. This is most effective for killing larvae of clearwing moths. Biological control options include the use of beneficial nematodes such as those from the Steinernema group.
Recommended insecticides for borers include products containing pyrethroids or carbaryl. For best efficacy, time the application of the chemical carefully to target the adults during the egg-laying stage before the larvae hatch and get a chance to enter the tree. Once the larvae bore inside the tree, they cannot be killed, even with the use of systemic insecticides such imidacloprid or acephate. In case of severe infestation, the best strategy is to remove tree entirely to protect other plants in the landscape.