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Oak Tree Pest Alert: Two-Lined Chestnut Borer

Written by John Sepulveda, Certified Arborist WI-1454A

The two-lined chestnut borer (TCB) may have an outdated name, but it can be big trouble for most species of oak, especially the bur oak. This native pest causes the death of many oak trees within two to three years. Oak trees that are stressed by heat or drought are vulnerable. And, issues may be showing up this year after last year’s dry, hot summer. Here are answers to frequently asked questions about TCB.

Q: What does TCB look like?

A: The adult can be up to a half-inch in length with a blackish body and a yellow stripe down both sides of the body. These characteristics are not present in other species that are closely related, such as the emerald ash borer (EAB) and bronze birch borer. It attacks trees in much the same way - by damaging the vascular system so water cannot reach the upper canopy of the tree. Eventually the lower parts of the tree will also die from lack of water.

Q: Why would it attack my oaks if it is a chestnut borer?

A: Good question. Chestnut trees and oaks are in the same family. After the chestnut blight in the early1900s made chestnut trees nearly extinct, oaks have become a main host for the beetle. We are lobbying for a name change for this insect!

Q. How can you tell the difference between TCB and oak wilt?

A. One difference is the presence of D-shaped exit holes that are made by the adults when they mature. However, the holes are first present higher in the canopy due to the top-down mode of infestation similar to other borers. Since most people doesn’t often climb into the upper parts of the canopy, a sign of TCB that's easier to recognize is brown and wilted foliage that has not dropped off branches. They foliage usually stays attached for weeks or even months. Oak wilt on the other hand causes the leaves to turn brown and then drop sooner than leaves in a tree affected by TCB.

Q. Can oak trees with TCB be treated?

A. Keeping your oak trees healthy is one of the best methods of preventing infestation. The beetle attacks trees that are weakened due to drought, damage, or other pests and diseases. However, pesticide treatments can also reduce population numbers and are a good option.

If you notice leaves wilting or browning on your oak, give us a call at 414.257.2111. One of our certified arborists will come to inspect your tree, make a diagnosis and recommend treatment options. As a full-service tree care company celebrating its 50th year in business, saving trees is one of our aims. Schedule a visit today!

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