Bronze Birch Borer

Bronze Birch Borer

Bronze birch borer Agrilus anxius is native to North America and is considered a serious pest to Species of birch. Some Birch trees are more resistant to bronze birch borer. Bronze birch borer is really considered a secondary problem. The pest usually attacks trees that are stressed or weakened from disease, drought, mechanical injury, poor planting site…therefore vigorous healthy trees are more unlikely to be consider a viable host.

Affected trees: White, Paper, European white birch as well as many other species of birch

Noticeable Signs

Common signs of bronze birch borer tend to show:

  • thinning or branch dieback within the upper third of tree is an initial sign of a bronze birch borer infestation.
  • leaves on an infested tree may appear smaller than usual and brown along the edges in late May or June.
  • bronze birch borer’s leave small 1/8 inch d-shaped exit holes as they emerge in adult form sometime between May-July.

Treatment/Management

Larvae from bronze birch borers pupate in late spring and emerge from the tree as adults sometime May through July.  Females typically only live for 3 weeks and deposit their eggs within cracks or loose bark of a tree. The eggs hatch within two weeks as larvae and burrow into the tree and feed on inner bark and outer wood layers sometime until late fall.

From a preventive standpoint, we recommend treating bronze birch borer with an annual soil injection of Imidacloprid in fall as the larvae feed. If the problem is identified in spring to early summer, a three application foliar spray can used in conjunction with a fall soil injection.