Northern WI Forest Health

Squirrels Can Damage Trees During Late Winter

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Photo showing that squirrels have removed significant amounts of bark from a maple tree's trunk to get at the tasty cambium layer underneath.

Squirrels have removed significant amounts of bark from this maple to get at the tasty cambium layer underneath. / Photo Credit: Linda Williams, Wisconsin DNR

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

Squirrels can be fun to feed and fun to watch, but when they start damaging or killing your trees, well, that’s not so cute.

It’s the time of year when we start to have some warm days that allow sap to start moving in trees. If there are broken branches or damaged bark, the tree can drip sap. And that can attract squirrels.

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Squirrel Or Porcupine Damage: How Do You Know?

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Photo showing squirrel tooth marks on a tree. Squirrel tooth marks are small and look like narrow scratches where the animals have removed the tree’s bark.

Squirrel tooth marks are small and look like narrow scratches where the animals have removed the tree’s bark. / Photo Credit: Linda Williams, Wisconsin DNR

By Linda Williams, Forest Health Specialist

Linda.Williams@wisconsin.gov or 920-360-0665

If something chewed the bark off your tree, how would you go about determining the culprit?

Quite a few animals can damage bark on trees, from deer and bears to rabbits and mice. But the damage from squirrels and porcupines can look very similar, especially from a distance. So, how can you tell the difference?

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Frost’s Bite: How Do Insects Survive Winter?

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An emerald ash borer larva overwinters by curling into a J shape inside a channel in an ash tree in Brookfield in 2019.

An emerald ash borer larva overwinters by curling into a J shape inside a channel in an ash tree in Brookfield in 2019. / Photo Credit: Bill McNee, Wisconsin DNR

By Michael Hillstrom, DNR Forest Health Specialist, Fitchburg

Michael.Hillstrom@wisconsin.gov

As winter’s chill persists, Wisconsin Department of Natural Resources (DNR) Forest Health staff members are often asked how cold it needs to get to kill insects, especially invasives.

The answer varies from species to species, but many insects are well adapted to dealing with freezing winter temperatures. Some, such as monarchs, avoid the issue and migrate south for the winter. Others, such as multicolored Asian ladybeetles, annoy us with their presence in our homes and offices as they try to avoid the cold until spring.

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What Are Those White Fluffies On Trees?

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Lots of beech scale, covered in white wool, makes this tree’s bark look fluffy.

Lots of beech scale, covered in white wool, makes this tree’s bark look fluffy. / Photo Credit: Linda Williams, Wisconsin DNR

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

Last month, we introduced readers to the woolly alder aphid, which is easier to spot in the winter as the insects congregate on alder branches and grow strands of white, waxy material to cover themselves for winter.

But there are other white, fluffy things that you might notice on tree bark or branches as well.

Beech scale, the insect associated with beech bark disease, is covered in white wool and remains on the tree throughout the winter. In areas with high beech scale populations, the beech trees can be so white with insects that the bark looks white, like a birch.

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Woodpecker Flecking On Ash Means EAB

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Photo showing that woodpecker flecking on green ash and white ash, from birds feeding on emerald ash borer larvae, will often be extensive and very noticeable.

Woodpecker flecking on green ash and white ash, from birds feeding on emerald ash borer larvae, will often be extensive and very noticeable. / Photo Credit: Linda Williams, Wisconsin DNR

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

Ash trees that are flecked by woodpeckers will have the outer layers of their bark chipped off by the birds. Woodpeckers do this to punch through the remaining bark more easily to get at the tasty emerald ash borer (EAB) larvae living there.

Flecking usually starts at the top of the tree, providing a sure sign that insects are under the bark. Although the problem could be caused by ash bark beetles, the more common culprit is EAB.

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Impacts Of Winter Weather On Trees

Posted on by akabelowsky
A photo showing that heavy, wet snow can bend and deform small trees and cause branch breakage or whole tree failure of larger trees.

Heavy, wet snow can bend and deform small trees and cause branch breakage or whole tree failure of larger trees. / Photo Credit: Wisconsin DNR

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

Winter damage can significantly impact the health of trees. Keeping trees healthy through the fall is important for reducing winter stress. In dry falls, like the one Wisconsin experienced in 2024, you can help trees go into winter healthy by continuing to provide water to them until the leaves start falling (for deciduous trees) or until the ground starts freezing (for conifers).

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White Masses On Alder Are Woolly Aphids

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Photo showing a group of woolly alder aphids on an alder branch.

A group of woolly alder aphids on an alder branch. / Photo Credit: Linda Williams, Wisconsin DNR

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

Have you seen white lumps of fluff on alder stems? Woolly alder aphids congregate together for the winter. These aphids produce white filaments from their bodies to protect them from predators. When they congregate, they can look like a big clump of snow stuck to alder branches.

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Forest Health Staff To Join Oak Disease Webinar

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A screen grab of a webpage on the United States Environmental Protection Agency website discussing a pest management webinar set for Dec. 10, 2024.

The U.S. Environmental Protection Agency will present an international webinar titled “Deadly Oak Diseases” from 1 to 2:30 p.m. Tuesday, Dec. 10. / Graphic Credit: U.S. Environmental Protection Agency

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

The U.S. Environmental Protection Agency (EPA) will present an international webinar titled “Deadly Oak Diseases” from 1 to 2:30 p.m. (CST) Tuesday, Dec. 10.

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Check Conifers For Invasive Adelgids

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Photo showing white, cottony hemlock woolly adelgid egg sacs on a hemlock branch.

White, cottony hemlock woolly adelgid egg sacs on a hemlock branch. / Photo Credit: Bill McNee, Wisconsin DNR

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

Hemlock woolly adelgid (HWA) and balsam woolly adelgid (BWA) are invasive, aphid-like insects that cause tree mortality in North America. Neither has been found in Wisconsin so far, but they are likely to arrive at some point, as they have been confirmed in Michigan.

HWA (Adelges tsugae) is an invasive, sucking insect pest of hemlock trees. The white, cottony egg sacs of HWA can be seen on the undersides of hemlock branches at the base of needles year-round. HWA saliva enters the tree while feeding. The saliva is toxic and causes needle drop and twig dieback, progressing to tree mortality in 4-10 years.

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Heterobasidion Root Disease Found In Door County

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Two photos of the same spot on a tree in Door County, showing Heterobasidion root disease fruiting bodies (left) and the basal wound beneath them (right).

Two photos of the same spot on a tree in Door County, showing Heterobasidion root disease fruiting bodies (left) and the basal wound beneath them (right). / Photo Credits: Bill McNee, Wisconsin DNR

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

Heterobasidion root disease (HRD), formerly known as annosum root rot, was recently found in Door County for the first time.

In mid-September, several suspected HRD fruiting bodies were spotted in a white spruce plantation on privately owned land in the town of Sevastopol. One cluster of fruiting bodies located at the base of a dead spruce was confirmed as Heterobasidion irregulare, the fungal pathogen that causes HRD. The other fruiting bodies were identified as a native decay fungus that has a similar appearance.

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