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Borers are chewing insects, usually in larval stages, that chew and feed on the inner bark and/or wood of trees. Many species are the larvae of various beetles. Some are wood-boring caterpillars and a few are wasps.


Vulnerable landscape plants that should be monitored closely for borer attacks include [ash, azalea, birch, black locust, cherry, dogwood, elm, honey locust, lilac, maple, mountain ash, oak, pecan, pine, plum, polar and rhododendron.] Be aware, however, that almost every tree species has a borer that can attack it. Borers are particularly destructive to newly planted trees and those in poor health.

Biology and Symptoms:

Borers feed unseen inside the roots, trunks, branches and twigs of many trees. They girdle the vascular system and disrupt the normal flow of water and nutrients., and/or weaken wood so it is more susceptible to breakage.

The first signs of a borer attack are often sawdust-like material and/or sap and resin oozing from small holes in tree trunks or branches. Bark appears swollen, knotty and callused, and may develop cracks that eventually cause small areas to break off. Leaves in the upper part of the tree are undersized and discolored, and twigs and small branches begin to die.


The best way manage borers is by keeping the tree healthy in the first place, by proper fertilizing, mulching, watering and controlling other insects and diseases. These practices will help increase your tree’s tolerance or avoidance to borer attacks, and help it recover if borers are already present.

Some borers are susceptible to treatments depending on the species, infestation severity, and health of the host tree.  Trees with advanced infestations are often not salvageable.

Help reduce the chances of borers harming your trees by contacting your local arborist for an inspection.

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