Northern WI Forest Health

Watch For Hemlock Woolly Adelgid

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

Landowners with hemlock and anyone who walks through or works in hemlock stands can help watch for signs of hemlock woolly adelgid (HWA).

This invasive insect has not yet been identified in Wisconsin, but it has been found in seven counties in Michigan’s Lower Peninsula. The insect sucks the sap of hemlock trees, and large populations can cause the decline and mortality of hemlock over 4 to 10 years, depending on the health of the tree and population levels of HWA. It’s vital to find infestations as early as possible to allow multiple options for control and management.

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Slime Mold: Mysterious And Amazing

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

What can learn new things, move toward and acquire food, remember where food was and what foods are preferred, figure out the shortest route through a maze, remember where it has traveled and seem to disappear as quickly as it first appeared?

It’s slime mold, of course!

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Emerald Ash Borer Spreads Through The North

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By Paul Cigan, DNR Forest Health Specialist, Hayward;
https://dnr.wisconsin.gov/topic/foresthealth/staff, 715-416-4920

This winter, the spread and impact of emerald ash borer (EAB) have been confirmed in several new northern townships in previously invaded counties.

These include Marengo (Ashland County); Gordon, Hawthorne and Oakland (Douglas County); Cadott and Colburn (Chippewa County) and Balsam Lake and St. Croix Falls (in Polk County).

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Feeding Aphids Cause Spruce To Wilt

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

Have you ever wondered just how much sap can be sucked out of a tree by aphids?

Aphids insert their piercing, sucking mouthparts into needles, twigs or bark, depending on the species of aphid.

Once their mouthparts are inserted, they begin to suck sap and will excrete excess moisture as small droplets of water called honeydew.

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Squirrel Damage To Maple Trees Showing Up Earlier This Winter

Posted on by akabelowsky

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

Photo of a maple tree with some bark removed by squirrel feeding.

Squirrels have stripped off the bark of this maple tree to get at the sweet cambium layer under the bark. / Photo Credit: Linda Williams, Wisconsin DNR

Typically in the spring, squirrels can cause damage to maple trees by removing bark from branches and the main stem after the trees have been frozen all winter and the weather starts to warm up. This fall, before the January cold spell, temperatures had warmed up by mid-November and remained warm throughout December.

As a result, starting in late November fresh squirrel damage was being noted on some scattered maples in north central Wisconsin. Damage progressed throughout December and some trees have more than half of the bark removed from branches and the main stem. The sight of scattered bits of bark around the base of these trees is another sign of squirrel activity.

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Woodpecker Damage On Ash Trees May Indicate Emerald Ash Borer

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By Bill McNee; DNR Forest Health specialist, Oshkosh;
Bill.McNee@wisconsin.gov or 920-360-0942

Photo showing woodpecker damage on an ash tree trunk, an early sign the tree might be infested with emerald ash borer.

Woodpecker damage is an early sign an ash tree might be infested with emerald ash borer. / Photo Credit: Wisconsin DNR

The Wisconsin Department of Natural Resources (DNR) encourages property owners to watch for woodpecker damage to their ash trees this winter. If damage is found, property owners should make plans to take action in the spring.

Woodpecker damage, often called “flecking,” happens when birds peck away some of a tree’s bark to access the larvae underneath. Flecking is a common early sign that an ash tree might be infested with emerald ash borer (EAB), an invasive insect. EAB is the most damaging threat to Wisconsin trees, killing more than 99% of the untreated ash trees it infests.

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Leafminer Creates Green Bay Packers Colors On Aspen Leaves

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Photo of an aspen leaf that fell in the fall showing a “green island” due to leafminer feeding.

An aspen leaf that fell in the fall showing a “green island” due to leafminer feeding. / Photo Credit: Linda Williams, Wisconsin DNR

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

Most aspen leaves that fell this fall were a beautiful yellow gold color, but every so often some could be found that were yellow with a green strip on them. Were the aspen trees supporting the Green Bay Packers? No. The green stripe was an indication of the presence of a tiny leafmining caterpillar.

Leafminers are tiny caterpillars that live and feed within a leaf. These tiny caterpillars may produce blotch mines or serpentine mines that create lines on the leaf.

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Forest Health Forecast For 2024

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

An aerial photo of oak and aspen forests showing heavy defoliation from spongy moth.

Oak and aspen forests with heavy defoliation from spongy moth. Additional defoliation coupled with ongoing drought in the upcoming 2024 growing season is expected to put significant stress on affected forests. / Photo Credit: Paul Cigan, Wisconsin DNR

Maintaining a healthy and productive forest often requires — more than ever before — a working knowledge of how to anticipate, prevent and mitigate environmental stressors that threaten to undermine it. The list of stressors includes drought, impact of forest insects and diseases.

In a recent and timely article, Denise Thornton of My Wisconsin Woods taps the expansive knowledge of the DNR’s Forest Health team and a state climatologist to bring focus to the threats facing forests this year.

She also lists steps that can be taken to ensure health and proactivity are maintained in your forests.

Bronze Birch Borer Attacks Stressed Birch

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

Photo of a white birch tree with its top half dying from bronze birch borer attack.

Bronze birch borer has attacked these trees, and parts of the tree above the attack site are thin and declining. / Photo Credit: Linda Williams, Wisconsin DNR

Bronze birch borer (Agrilus anxius) is a native beetle that attacks birch trees. As adults emerge from the bark, they create small, D-shaped exit holes, similar to emerald ash borer but smaller.

Bronze birch borer attacks stressed trees, and the source of the stress can be anything from drought, flooding, defoliation or old age.

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