What is a Bronze Birch Borer?
The Bronze Birch Borer, (Agrilus anxions), is a native flat-headed wood boring beetle which attacks Birch and Beech trees. Bronze birch borer adults are slender, dark, iridescent, often greenish-bronze, beetles.
This species spends the winter as larvae in a boat-shaped depression just under the bark of the tree. In early spring larvae molt into the pupal stage. During early June, adults chew their way through the bark and emerge, leaving the characteristic noticeable “D”-shaped hole. After mating, females lay eggs in cracks, beneath bark flaps, or other damaged areas. Eggs hatch in a few days into tiny white larvae that chew their way into the bark and start feeding.
Which Trees Are Most Vulnerable to the Bronze Birch Borer?
A healthy Birch can easily resist the Bronze Birch Borer, but those Birches affected by drought, injury, disease, sun scald, or poor soil quality are more susceptible. Normally birch trees enjoy cool, boggy surroundings, generally near water, so birches in more urban areas can also be more vulnerable.
Many birch trees like the yellow and grey, as well as white, paper, and cut-leaf weeping birches are at greater risk of bronze birch borer attack than others. For instance, the River Birch and Birches with a Brown Bark are more resistant to the Borer.
Identifying Bronze Birch Borer Infestations
The first indication that a tree is infested with borers is wilting and dying of the leaves in the upper crown, which is not obvious by casual looking. A closer look will reveal ridges and bumps on the branches and “D” shaped holes where the birch borer emerges one it matures. Another indicator can be a rusty brown stain. If you were to remove the bark where ridges are abundant it would reveal irregular, winding, sawdust-packed tunnels called galleries that are made by larvae excavating plant material from between bark and wood.
Saving Your Birch (or Beech) Tree from the Bronze Borer
If you have birch or beech trees that you value, you will want to take care to water and care for the trees to prevent borer attacks in the first place. By the time the affect on the tree is visible, it may be too late to treat them. There are also preventative treatments that may be applied.
Trees with symptoms in less than a third of the canopy are a good candidate for treatment, but beyond this point, the vascular system of the tree becomes so compromised that treatments will be ineffective. All dead branches should be removed.
Spring or Fall are the ideal time to apply treatments to the tree, and should be done for valued, vulnerable birch trees yearly.