Borer Invades Area Trees

Beetle seems to prefer red oaks

BAXTER - A beetle infestation is cutting a killing swath through lakes area oak stands and may be most noticeable near the Whipple Beach area in Baxter.

Defoliated dead and dying trees stand in stark contrast to the green leaves on healthy tree neighbors. The culprit is the native beetle called the twolined chestnut borer. While its name suggests the chestnut tree is a first choice, those trees are in short supply. Second on the beetle menu here are all varieties of oaks, with preference given to red oaks.

The opportunistic beetle attacks weakened oak trees. The DNR reports when trees are healthy the beetle will confine its attack to less robust trees or broken branches.

Jake Frie, Crow Wing County forester with a master's degree in natural resource science and management from the University of Minnesota, said the recent drought years weakened oaks, particularly those in more dense stands where they compete for nutrients. Crow Wing County manages the acres of trees by Whipple Beach and nearby Camp Vanasek.

In Baxter, Frie said the Whipple Beach area represents a large visible and dramatic pocket but there are oaks all over that are affected by the beetle, likely thousands of acres.

The DNR reports the first tell-tale signs of infestation may not be visible until mid-July. Adult beetles lay eggs on weakened oaks in late May and June and throughout the summer the larvae eat the inner bark ultimately destroying the tree's ability to move water and nutrients up its trunk.

Leaves turn brown and stay on the tree. The larvae over winter in the tree and come out the following spring in D-shaped exit holes. And the cycle is repeated.

The DNR said the affected trees have a pattern of "dead, red and green," from top to bottom - meaning the tree top is dead or leafless, the middle crown has red-brown wilted leaves and the green bottom section is still alive.

Frie said the county's plan for the Whipple Beach area is focusing on the full-grown larvae. Individuals have been given firewood permits where for $20 they can take up to 10 cords of dead or downed timber. Small branches are not a concern for reinfestation as the larvae need something living or recently dead and large enough that it won't quickly dry out.

The infected timber should be burned before May when the larvae will emerge from the tree. Or Frie said the wood pile can be covered by a tarp with the bottom edges covered by dirt. When the beetles emerge in the spring or early summer, they will die under the tarp.

"That's all it takes," Frie said.

Earlier in the year, pruning may help and may sometimes save the tree. Frie said people with fewer trees may be able to more aggressively fight the beetle than forest managers responsible for hundreds of acres.

Options for management include watering trees to reduce stress, pruning and cutting down trees that are less vigorous or showing little growth in order to let stronger trees spread out their canopies and thrive. Having diverse tree species also helps so one infestation is unable to wipe out an entire area.

In the Whipple Beach and Camp Vanasek areas, Frie said the plans are to plant white pine and white spruce - species appropriate for the site - in the areas where the oaks are cut down.

For more info go online to the DNR Web site - www.dnr.state.mn.us/treecare - for information about tree health, how to recognize symptoms and to learn about management options.

RENEE RICHARDSON may be reached at renee.richardson@brainerddispatch.com or 218-855-5852.

These oak trees near Whipple Beach in Baxter are nearly devoid of leaves. They may be one of the most visible pockets of an infestation of twolined chestnut borer beetles, but oak trees throughout the area, already weakened and stressed by drought years, are prime targets for the native beetle. (Brainerd Dispatch/Kelly Humphrey)