I got a call a few years ago from one of my readers. His Paper Bark Birch was in severe decline.
From what I could see, this two-foot-diameter tree was dying. I explained the dire situation of the tree to the homeowner. He decided to take down the tree.
The way the trees die from this insect is that the insect girdles the tree, specifically the sap-conducting part, and slowly kills the tree. Once you notice the paper bark birch withering at the top of the tree, it will take from two to three years for the tree to die.
According to Joe Boggs of the extension service, foreign birches, such as the European White Birch, are the most susceptible to this insect. Natives are much less vulnerable.
From the D-shaped holes and the wilting in the tree, I decided that the tree had all of the characteristics of the Bronze Birch Borer or Agrilus anxius ‘Gory’. People select the foreign birches, the European white birch, and the Jacquemonti birch for the white bark over the native birches.
This borer is a slender beetle that is one-half inch long. Nursery growers raise fewer European White Birch because of this insect. Bronze birch borer, a native of Ohio, ranges from coast to coast in Canada.
It also permeates Ohio, Colorado, Idaho, and Oregon. European white, water, paper, canoe, and yellow birch are susceptible.
Gray birch is moderately vulnerable. Yellow scout sticky pads/traps will help determine if other trees are affected.
The larvae bore into the sap-bearing part of the wood and kill the tree by girdling it, so that no sap can pass through the blocked areas.
Therefore, the tree, starting from the top, will appear to be wilting. As the insect population continues to grow, more branches will die from the top down, ultimately leading to the entire tree’s demise.
The adults are dark olive bronze in color, with bright green iridescent color underneath the wing covers, measuring from three-eighths to one-half inch in length. These are fast, secretive beetles.
One identifying characteristic of this borer is its flat head and segments behind the head. A stressed birch planted in full sun in a well-drained or dry location is the dinner bell for this insect.
This birch performs better in shaded and semi-moist areas, and a fertilizing program will help this tree resist the attack of this insect.
In northern Ohio, we can expect to see insects emerging from mid-May to late June, leaving a D-shaped hole and feeding on the edges of the leaves before laying eggs.
The females seek crevices in the wood to lay their eggs. As the insect larvae hatch 10 to 14 days later, they burrow into the wood through less dense portions of the bark. The adults lay their eggs in these crevices. Larvae form pupae in the fall just beneath the bark.
During the initial phases of attack, most egg-laying is concentrated in the upper crown on branches less than one inch in diameter. This insect attacks larger branches and ultimately the trunk as infestations progress.
Eggs hatch in two weeks, and the larvae enter the cambium, where they spend most of their lives. You usually won’t find them in the xylem. Larval galleries often eat zigzag patterns in the wood and are packed with fine sawdust frass.
Pupation occurs in late April and continues into May, marking the start of a new cycle.
From mid-May through July, attacking feeding adults on the leaves and young larvae as they enter the sap or cambium layer of the wood can provide some success. The bronze birch borer takes one to two years to complete its life cycle.
You should apply protection sprays by early June and again in early July to control larvae.
To kill the larvae, you can also spray, drench, or inject the insecticide as the larvae feed from late June to mid-September with a systemic.
There are several chemical solutions for the bronze birch borer, such as Carbaryl, when applied appropriately. Imidacloprid, a systemic insecticide, can be applied by you in several ways to control this insect.
Using these compounds may have a detrimental effect on pollinators. I recommend removing damaged trees promptly to interrupt the insect’s life cycle and selecting native birch over non-native replacements.
Bouncing out Bronze Birch Borers begins with identification. Birches are beautiful and deserve our bother.
I hope you all have had a pleasant stroll through your garden this week. If you have any questions, you can e-mail me at ericwlarson546@yahoo.com.