About this Tree Concern
The Bronze Birch Borer is a beetle native to North America that can cause significant harm to birch trees, particularly those that are already stressed or weakened. The primary damage is done by the larvae, which feed beneath the bark and disrupt the flow of water and nutrients within the tree. The more evident signs that a tree has been attacked by bronze birch borer are thinning, yellowing, and eventual dieback of the upper crown as well as smaller leaf size and subsequent browning. The tree trunk may heal with swelling or lumpy bark showing on the outside of the tree, or may girdle and kill branches or trunks. Leaves may be yellow as a result of damage done in the tree trunk. Bronze Birch Borers attack trees weakened by age, environmental stresses, or previous insect attacks. A birch infested with the Bronze Birch Borer beetle will start showing dying leaves in the crown, increasing in severity as the infestation continues, often leading to death of the tree.
Infestations of Bronze Birch Borers cause tree crown dieback, usually starting at the top of the tree and work downward; the European white birch is a favorite host.
Remediation
Proper care of birch trees decreases the likelihood of infestation. Sickly or weakened trees are more likely to be attacked by borers so keep trees growing vigorously with adequate water and fertilizer. In healthy trees, the sap flow can act as a defense and drown borers as the sap fills holes bored by the larvae.
If you discover evidence of bronze birch borer, prune any infested branches. Pruning is best done early spring when larvae are developing and infected branches should be properly disposed of well away from the infested tree.
An insecticide can be applied to the shoots and bark to kill adults and newly hatched larvae before they bore into the bark. Adults do not feed significantly on the leaves so it is not necessary to treat the foliage. Timing of insecticide applications is important because once the larvae bore into the bark they are out of reach of insecticides. Some insecticides will need repeat applications so follow the label recommendations.