Northern WI Forest Health

Impacts Of Winter Weather On Trees

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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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Winter Squirrel Damage Killing Maple Branches

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

Two photos show maple branches that died recently due to previous damage from squirrels.

Two photos show maple branches that died recently due to previous damage from squirrels. / Photo Credit: Linda Williams, Wisconsin DNR

Have you noticed maple branches suddenly dying this summer?

Sudden mortality of maple branches during the summer in northern Wisconsin is often a result of squirrel damage that occurred in late winter and early spring.

In late winter and early spring, gray squirrels strip the bark of maples to get at the sweet maple sap. When the damage is extensive or severe, entire trees or branches will be killed immediately and will not leaf out in the spring.

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Jack Pine Budworm Outbreak Subsides

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

Aerial view of jack pine budworm defoliation in jack pine stands in Douglas County during the 2023 outbreak. / Photo Credit: Paul Cigan, Wisconsin DNR

Jack pine defoliation caused by the jack pine budworm (JPBW) continued at mostly light levels this year, affecting stands in the Central and Northwest Sands Ecological Regions of Wisconsin.

In the Northwest Sands, jack pine stands experienced light and scattered defoliation across Burnett, Douglas, Polk and Washburn counties. In the Central Sands, JPBW caused moderate to heavy defoliation across roughly 500 acres of jack pine on county and state forests in Jackson County, east of Black River Falls.

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Hemlock Monitored After 2023 Defoliation

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

Photo showing that hemlock crowns remained thin this summer at a Vilas County plot that saw defoliation by spruce budworm in 2023.

Hemlock crowns remained thin this summer at a Vilas County plot that saw defoliation by spruce budworm in 2023. / Photo Credit: Linda Williams, Wisconsin DNR

Spruce budworm was observed defoliating a stand of hemlock trees in Vilas County in 2023. This stand was revisited in 2024 and although defoliation was only light this year, significant thinning in the tops of hemlocks was noted.

Hemlock is not a preferred host for spruce budworm, and the defoliation in 2023 was due to an extremely high population of spruce budworm in that area.

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Squirrels Love Acorn Pip Galls And Weevils

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

Closeup photo of six acorns. One still has pip galls; the others have had their pip galls eaten by squirrels.

The acorn farthest on the right has pip galls. Squirrels ate the pip galls from the other acorns. / Photo Credit: Linda Williams, Wisconsin DNR

Several areas in northern Wisconsin have reported significant acorn drop. In almost all cases, these acorns have been damaged by either pip galls or acorn weevils.

Squirrels enjoy feeding on pip galls and will pluck those acorns off the tree, rip off the cap, eat the pip gall and drop the rest of the acorn to the ground. Squirrels will also seek out acorns infested by acorn weevils. They will open those acorns, eat the larvae and then drop the rest of the acorn to the ground.

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Larch Casebearer Damage Spotted In North

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

Photo showing a tamarack tree branch with severe needle mining from larch casebearer. / Photo Credit: Paul Cigan, Wisconsin DNR

A tamarack branch shows severe needle mining from larch casebearer. / Photo Credit: Paul Cigan, Wisconsin DNR

Larch casebearer has caused localized heavy defoliation in some tamarack swamps in central Burnett County this spring, causing tamarack to stand out with a stark appearance of bright-brown foliage by mid-June.

Larvae of this exotic moth damage tamarack needles by “mining” the inner needle tissue. Heavily damaged tamarack progress in color from pale green to yellow and eventually turn a bright, reddish brown as needles dry out and die.

 

 

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