The bronze birch borer, Agrilus anxius (Gory), can be a serious pest to birch trees. It is a native American insect that is especially prone to attack stressed ornamental birches. The damage is done by the larvae (worms) of the bronze birch borer. The larvae mine out feeding galleries in the inner bark and as these become extensive, the tree can essentially be girdled.
Indications of Infestation - Yellowing leaves and sparse foliage, most evident in the upper crown indicate a borer infestation. These symptoms may be accompanied by an increase in adventitious growth in the lower crown. Later the upper branches, and eventually the whole tree, will turn brown and die.
Life History - The borers overwinter as larvae in birch trees. In early spring they pupate and adults emerge in late June. The adults may feed minimally on birch leaves, however, they prefer alder leaves. Adult feeding is insignificant and rarely noticed. After mating, females lay eggs in the bark of birch trees. Injured areas of the tree are favorite sites for laying eggs. The larvae hatch, bore into the inner bark, and begin to create mines and feed.
Healthy Trees - Studies have shown that healthy trees can resist attack by these beetles. Trees that have survived attack may have a lumpy appearance--this is caused by the healing process.
To maintain the health of birch trees and enhance their ability to fight off beetle attack, keep trees well fertilized and watered. Prune out and destroy old, diseased, or damaged wood. Plant trees in favorable sites where they will not be exposed to excessive heat or drought. Avoid mechanical injuries to the bark and avoid using herbicides (weed killers) around the tree.
