Are Borers Killing Your Trees?

Identifying boring insects in time can save your trees

What to look for:

Frass is insect excrement, and often appears as dry, grainy material near insect feeding sites. Frass can accumulate around borer holes, and may even collect in piles at the base of heavily infested trees. The presence of frass mixed with the sawdust created by feeding is a sure sign of borer damage.

Crown Die-back:
One of the most obvious and common signs of borer damage is the gradual dieback of twigs and branches in the crown. Borer activity in the phloem and xylem can interfere with the flow of nutrients and water between the leaves and the roots, causing branches and twigs to die, resulting in either general dieback or flagging.

Exit Holes:
Carefully examining your trees for exit holes, which can be made by either fully formed adults or mature larvae that leave the host tree to pupate.

Wet Spots:
A tree’s first defense against a borer is often to produce sap, which is intended to smother or drive out the invading insect. This reaction may result in wet spots on the bark of the tree. Examine these wet patches carefully for other signs of borer damage, such as holes, frass, or sawdust.

Growth Irregularities:
Trees often respond to borer feeding by forming tough callus tissue around the wound, which may appear as irregular ridges or bumps below the bark. Borers that feed on shoots and twigs may cause unusual hooks or forks to form on the affected stem. Large swellings and the loss of bark can indicate severe borer damage as well.

Extensive borer damage can lead to breakage in twigs, branches, and even trunks. Severe borer damage often goes unnoticed until a wind storm snaps the trunk of a tree that has been riddled with borer holes.

Egg Deposition Sites:
While the eggs are usually too small to see, some boring insects chew pits or grooves in the bark that can be found upon close inspection.

Adults or Pupae:
In some cases adult insects can be found near the host tree. Those species that pupate outside the tree may create cocoons or pupae in bark crevasses or debris around the tree.

The most effective form of borer control is prevention. By monitoring high risk trees and applying the appropriate pesticides to eggs and newly hatched larvae the risk of severe borer damage can be reduced.

The best preventative treatment, however, is fertilization, watering, soil aeration, mulching, and other treatments aimed at increasing tree health.

Healthy trees are less likely to be selected as borer hosts and better able to defend themselves from borer attack.

More Tree Health Telltale Signs

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