Northern WI Forest Health

Oak Wilt Confirmed In Ashland County

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Map showing Wisconsin counties in which oak wilt has been detected.

With the addition of Ashland County, oak wilt has now been detected in 66 of Wisconsin’s 72 counties. / Map Credit: Wisconsin DNR.

By Paul Cigan, DNR Forest Health Specialist, Hayward
Paul.Cigan@wisconsin.gov or 715-416-4920

Oak wilt, a deadly disease of oaks, has been found for the first time in Ashland County.

The Wisconsin Department of Natural Resources (DNR) confirmed the find in wood samples from a red oak tree in the town of Gordon.

“There is always risk of oak wilt spread into new and relatively uninfested areas in northern Wisconsin, such as Ashland County, so it’s always best to practice oak wilt prevention wherever possible to significantly reduce that risk,” said Paul Cigan, a DNR forest health specialist based in Hayward.

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Avoid Ash Trees When Placing Deer Stands

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Photo of hunter climbing into tree-mounted deer stand.

It is important to place and maintain tree stands carefully as you prepare for the upcoming deer hunting season. / Photo Credit: Wisconsin DNR

By Bill McNee, Forest Health Specialist, Wisconsin DNR;
Bill.McNee@wisconsin.gov; (920) 360-0942

The Wisconsin Department of Natural Resources (DNR) cautions hunters to avoid placing deer stands in or near ash trees this deer hunting season.

Most ash trees in the southern half of Wisconsin, Door County and the Mississippi River counties are dead or dying from emerald ash borer infestation. Although emerald ash borer is not as widespread in other parts of the state, the invasive insect continues to be found at additional locations throughout the state and unreported infestations also are likely.

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Oak Mortality Increases In 2023

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Photo of a bur oak tree more than 100 years old showing canopy dieback and epicormic branching due to twolined chestnut borer

A bur oak more than 100 years old exhibits canopy dieback and epicormic branching caused by twolined chestnut borer. / Photo Credit: Wisconsin DNR

By Michael Hillstrom, DNR Forest Health Specialist, Fitchburg
Michael.Hillstrom@wisconsin.gov

White, red and bur oaks have been experiencing increased mortality in Wisconsin and neighboring states over the last few years.

The causes of mortality are varied, but two-lined chestnut borer (TLCB) is the most common culprit. Wisconsin has switched from a period of historically wet years (2017-2020) to drought conditions that have become more severe each year (2021-2023). Add in frost damage, storm damage, increased growing season length and aging forests and the environmental recipe exists for stressed oaks that are more susceptible to attack by insects and diseases.

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Another Ash Pest Found In Northern Wisconsin

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Close-up photo of an adult cottony ash psyllid.

A close-up photo of an adult cottony ash psyllid feeding on an ash leaf. / Photo Credit: Steve Garske, Great Lakes Indian Fish and Wildlife Commission

By Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665

As if black ash trees don’t have enough problems with emerald ash borer (EAB), another ash pest recently was found at several locations in northern Wisconsin.

In June, Great Lakes Indian Fish and Wildlife Commission (GLIFWC) staff noticed black ash with leaf curling and puckering, early leaf drop and dieback at one of their Climate Change Program’s long-term phenology study sites.

After working with DNR Forest Health staff to narrow down the possibilities, insect samples were collected and sent to P.J. Liesch, director of the University of Wisconsin-Madison Insect Diagnostic Laboratory, for official identification. He identified them as cottony ash psyllid.

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Pink-Striped Oakworm Population Remains Low

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Photo of a pink-striked oakworm caterpillar on a hand.

This large caterpillar, a pink-striped oakworm, has great camouflage and blends in with oak twigs very well. / Photo Credit: Linda Williams, Wisconsin DNR

By Linda Williams, DNR Forest Health Specialist, Woodruff;
Linda.Williams@wisconsin.gov or 920-360-0665

Pink-striped oakworm is a native fall defoliator. Fall defoliators affect the health of trees less than defoliators that occur in the spring.

Although literature states that high populations of this caterpillar can create significant defoliation, no defoliation was noted in the area this caterpillar was observed in Oneida County.

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Aphids Make Sticky Situation For Oak, Beech Trees

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Photo of Myzocallis oak aphids on a leaf, with an adult at the left.

Myzocallis aphids feed on the top side of oak leaves. An adult is pictured on the left. / Photo Credit: Linda Williams, Wisconsin DNR

By Linda Williams, DNR Forest Health Specialist, Woodruff; Linda.Williams@wisconsin.gov or 920-360-0665

and Bill McNee, DNR Forest Health Specialist, Oshkosh; bill.mcnee@wisconsin.gov or 920-360-0942

Aphids — and the honeydew they produce — have made their mark on trees in Wisconsin during 2023.

Midway through the summer, oak trees in areas of Vilas and Oneida counties were buzzing with activity. During September, beech trees in eastern Wisconsin became busy with a different species of aphid.

A look at the two situations:

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Pine Bark Adelgids Infest White Pines

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Photo of pine bark adelgids covered in white, waxy fluff on a white pine tree.

Pine bark adelgids covered in white, waxy fluff on a white pine tree. / Photo Credit: Wisconsin DNR

Michael Hillstrom, DNR Forest Health Specialist, Fitchburg
Michael.Hillstrom@wisconsin.gov

Pine bark adelgids are tiny, aphid-like insects that suck the sap of white pines. The bugs protect themselves from predators with a fluffy, white wax covering. Pine bark adelgids generate concern when thousands of them gather on white pines to feed, making the pine bark appear covered with sap.

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