Drought Stressed Oak Trees Showing Signs of Beetle Infestation

(KNSI) — Oak trees stressed by the recent drought have been showing symptoms of a beetle infestation.

The Minnesota Department of Natural Resources says twolined chestnut borer is being found in many oak trees. The larvae feed beneath the bark of oak trees. While healthy trees are usually not infested, trees stressed and weakened by drought are especially vulnerable.

“Even when hot, dry weather is replaced by rainy days, it can take years for trees to recover after a drought,” said Val Cervenka, DNR forest health coordinator. “After two consecutive years of drought conditions in 2021 and 2022, we expect to see oak trees dying from twolined chestnut borer attack for the next few years.”

Symptoms of an infestation often begin in mid-July. Initially, they include dead and dying leaves at the top of the tree. Dead leaves can stay on branches for months. During the year following the attack, the top of the oak tree will be dead and leafless; leaves in the middle section die, become orange-brown and stay on the tree; leaves at the bottom will still be green.

If the tree has been infested for more than a year or two, it might be possible to find small, D-shaped exit holes in the trunk where the adult borers have come out of the tree.

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