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What is Bronze Birch Borer?

Updated: Apr 19, 2022

Written by John Sepulveda, Certified Arborist WI-1454A

Bronze Birch Borer (BBB), Agrilus anxius, is one of the many pests trees in Wisconsin must content with. A relative of the Emerald Ash Borer, it targets stressed trees that are less likely to fight off infestation.

BBB is native to North America so it won’t be going away anytime soon. It causes several birch species to die within only a couple years, sometimes sooner. Of the common species of birch in Wisconsin, white birch such as paper birch are more susceptible than other birches like river birch and varieties that have been selectively bred to be more resistant to the beetle.

How does Bronze Birch Borer kill my tree?

BBB causes damage to the phloem, the sugar transport cells of the tree, and cuts off the roots from the leaves, thus causing leaf die back and stress due to lack of nutrients. The roots dying causes the tree to not get enough water and eventually results in death.

How can I tell if my tree is infected?

A noticeable sign of their presence is defoliated branches in the upper canopy and chlorotic, yellowed, leaves. Less noticeable signs are zigzag tunneling beneath the bark, and small D-shaped exit holes made by the adults upon completion of the larval and pupae stage.

So, what can I do?

No one wants to lose a tree in their landscape, especially if it is the only source of shade or is a cherished tree planted by family members. Treatment can be given in the form of pruning of dead sections of the tree to reduce the BBB population that will be present to lay eggs.

Although this is an effective way to make your tree look better aesthetically, the best method to keep the beetle at bay is preventative. Keeping your birch well-watered and unstressed will give it a better chance to resist infection and make it easier for the tree to fight off the bug.

Another method which we provide is an insecticide treatment. This treatment is given as soil injections or trunk injections to kill the insect in the larval stage, which is the stage that does the most damage to the tree. These treatments assist your tree by keeping population numbers low.

If you are concerned about the health of your birch trees, request a tree inspection by Hoppe Tree Service. One of our certified arborists can inspect your trees, diagnose any potential problems, and recommend preventative services or treatment if needed.

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