Bronze Birch borer insect is mainly a pest of European White Birch tree, but it can also affect Gray Birch, Paper Birch and Yellow Birch. The adult beetle is about one inch long and is metallic bronze/copper in color.
Damage is done during the larval (caterpillar) stage. Adults lay eggs on the outer bark of the tree, ideally near an area of recent mechanical injury (i.e. a nick from a lawn mower or weed whacker, a broken branch or twig, an area where branches are rubbing against one another). When the eggs hatch, the larvae chew their way into the cambial zone where they spend up to two years feeding in a serpentine pattern. This feeding pattern disrupts the vascular flow of the tree, effectively girdling the stem or branch where the insects are feeding and the tree begins to decline.
What to look for
When adults emerge from the tree in late May/ early June, they leave behind a distinctive “D” shaped exit hole. Early symptoms of the presence of Bronze Birch borer appear in the upper crown as sparse foliage which is often accompanied by chlorotic leaves. As the infestation progresses, branches begin to die back from the tip followed by whole branch and stem loss leading to eventual death of the tree.
The best method of control is to prevent this insect from getting a foothold in your tree. You do this by keeping your tree in a healthy, vigorous growing condition. Follow good cultural practices:
- Create an adequate mulch bed
- Do not allow your tree to become moisture stressed or defoliated by leaf eating insects
- Appropriate fertilization/ beneficial fungi and bacteria soil treatments can be very helpful in maintaining a healthy soil environment in which the tree lives
Proper planting techniques as well as proper planting location will play a critical role in the plant’s health and vigor as it matures. Chemical control measures can target the adult beetle as a foliar spray application or a stem and branch spray application to control larvae just after they hatch. Most arborists I know control this pest preventatively using a chemical injection targeting the larvae as they begin to feed within the vascular tissue of the tree.
Birch trees are a short lived tree; most live only fifty to sixty years, but they are a beautiful landscape planting. Keep them stress free and there is a good chance you will keep them borer free as well.