Tree borers are chewing insects, usually in larval stages, that chew and feed on the inner bark and/or wood of trees. Most species are the larvae of beetles. Some are woodboring caterpillars or other insects.
Almost every species of tree may be susceptible to borers under favorable circumstances. Tree borers are particularly destructive to newly planted trees and those in poor health because of drought, root injury, weakening from other insects or disease, physical injury, or other environmental stresses.
Borers feed unseen inside the roots, trunks, branches, and twigs of many trees. Depending on species, they girdle the vascular system and disrupt the normal flow of water and nutrients, or weaken the wood to the point where the structure of the tree is compromised. 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 branches begin to decline and die.
The best way to manage tree borers is by keeping the tree healthy in the first place, by properly fertilizing, mulching, watering.