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Take Advantage Of Mild Winter Days To Prune Trees

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An arborist uses climbing safety gear to prune an oak tree along a road.

An arborist uses climbing safety gear to prune an oak tree along a road. / Photo Credit: Wisconsin DNR

By Mike Hillstrom, Forest Invasive Pest Coordinator, Fitchburg
Michael.Hilstrom@wisconsin.gov or 608-513-7690

Winter is an ideal time to perform trimming, cutting and brush removal work on and near trees, especially oak trees.

Winter is the best time to prune because the insects and diseases that attack oak trees, such as oak wilt, are not active. Pruning and other work can be done around oak trees from after the first hard freeze in the fall until the high-risk period for oak wilt begins in April.

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Stumping Heterobasidion Root Disease With Cellu-Treat®

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Photo of a freshly cut tree stump after treatment with fungicide to prevent infection with Heterobasidion root disease. The fungicide is dyed blue to help ensure complete coverage.

A freshly cut tree stump after treatment with fungicide to prevent infection with Heterobasidion root disease. The fungicide is dyed blue to help ensure complete coverage. / Photo Credit: Wisconsin DNR

By Tim Shively, DNR Forest Health Specialist, Eau Claire
Timothy.Shively@wisconsin.gov or 608-772-6974

Treating freshly cut conifer stumps is critical to preventing infection by Heterobasidion species, causal agents of Heterobasidion root disease (HRD).

Within this genus, H. irregulare is believed to be the only species in Wisconsin, and it causes the mortality of overstory pine and spruce trees. The DNR has developed comprehensive guidelines to assist landowners, property managers, foresters, and loggers with determining whether stump treatments are necessary to prevent the introduction or spread of HRD at a given site.

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Did You Know? Facts About Pine Webworm

Posted on by akabelowsky

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

Webbing and a collection of frass (caterpillar excrement) around these cones is the web nest of pine webworm. / Photo Credit: Wisconsin DNR

Pine webworm (Pococera robustella) is a native moth whose caterpillars feed on pine needles. In Wisconsin, the caterpillars prefer young jack pine and red pine. A single generation per year occurs in Wisconsin.

Young larvae mine needles, feeding within the needle. Older larvae form a compact web that they fill with small, oval pieces of frass. In early fall, the larvae drop to the ground to pupate and spend the winter.

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Keep It Local When Stocking Up On Firewood For Winter

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Photo of a firewood stand at Potawatomi State Park

A stand at Potawatomi State Park offers local firewood for sale to campers. / Photo Credit: Wisconsin DNR

By Wisconsin DNR

With the onset of autumn, many Wisconsinites have been making plans to stock up on firewood for the winter.

With that in mind, the Wisconsin Department of Natural Resources (DNR) is reminding residents and visitors about the year-round importance of obtaining firewood from local sources — whether it’s to heat your home in the winter or build a campfire in the summer.

The message is important enough that October has been designated National Firewood Month, and the DNR offers a webpage to explain firewood regulations, best practices and the reasons behind those guidelines.

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Beech Blight Aphids Visible In Eastern Wisconsin

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A photo of beech blight aphids found on a beech twig at Kohler-Andrae State Park in Sheboygan County.

Beech blight aphids are found on a beech twig at Kohler-Andrae State Park in Sheboygan County, Sept 5, 2025. / Photo Credit: Wisconsin DNR

By Bill McNee, DNR Forest Health Specialist, Oshkosh
Bill.McnNe@wisconsin.gov

Late summer and fall is the time of year when fluffy “beech blight aphids” become very noticeable on American beech trees (Fagus grandifolia) in the eastern quarter of Wisconsin, where the tree species occurs.

These large aphids grow white, waxy filaments from their abdomens and feed in a colony on the branches of beech trees. When disturbed, they all shake their abdomens in an attempt to scare off predators. This behavior has led to the insect being commonly known as the “boogie woogie aphid.”

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Cottony Ash Psyllid Found In Additional Areas

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Closeup photo showing how cottony ash psyllid nymphs feed on the lower sides of leaves and grow white wool over themselves for protection.

Cottony ash psyllid nymphs feed on the lower sides of leaves and grow white wool over themselves for protection. / Photo Credit: Wisconsin DNR

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

Cottony ash psyllid (Psyllopsis discrepans) was observed in 2023 in several areas in northern Wisconsin. Additional sites were then identified in 2024 and this year.

Some provinces in Canada have observed that psyllid numbers can explode during dry periods, so that may be why we started to see some issues in Wisconsin in 2023.

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Hail Damage Can Cause Dieback, Whole-Tree Mortality

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Photo of a young aspen showing signs of severe impact from hail. Arrows indicate each point of impact.

A young aspen shows signs of severe impact from hail. Arrows indicate each point of impact. / Photo Credit: Wisconsin DNR

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

Several high-impact storms across the state this summer have pummeled trees with hail. The photos accompanying this article show the kind of damage hail can bring to forests.

The initial damage following a significant hailstorm can immediately appear severe. But give it a month or two, and the damage can look even more pronounced.

Pines in particular will start to turn varying levels of brown, depending on the amount of damage they sustained. Damage to the branches and twigs is not limited to just the spot where the hail hit. As the summer goes on, damaged areas of bark that were cracked by the hail impact will often split open further and allow more drying and additional separation of the bark from the wood, which kills that area of the branch.

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Bur Oak Blight Confirmed In Calumet County

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Photo of a wedge-shaped area of dead tissue at the tip of a bur oak leaf from a tree infected with bur oak blight.

A wedge-shaped area of dead tissue at the tip of a bur oak leaf from a tree infected with bur oak blight. / Photo Credit: Wisconsin DNR

By Bill McNee, DNR Forest Health Specialist, Oshkosh
Bill.McNee@wisconsin.gov

Recent laboratory examination has confirmed the presence of bur oak blight in Calumet County. The disease affects only bur oaks and is caused by the fungus, Tubakia iowensis.

Calumet County is the 35th Wisconsin county to have a confirmed detection of bur oak blight. The disease has not been microscopically confirmed in all counties where bur oak grows and is likely present in additional counties. Bur oak blight was first reported in Midwestern states in the 1990s.

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HRD Conks Found In Different Shapes And Sizes

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Photo from above showing Heterobasidion root disease growing from an infected tree stump.

Heterobasidion root disease grows from an infected tree stump. / Photo Credit: Wisconsin DNR

By Kyoko Scanlon, DNR Forest Pathologist, Fitchburg
Kyoko.Scanlon@wisconsin.gov

Fall is a great time to look for mushrooms, including conks from trees infested with Heterobasidion root disease (HRD).

Considered one of the most destructive diseases of conifers in the northern hemisphere, the fungus causing HRD is very difficult to eradicate once established. Infestation of a conifer stand may significantly impact stand management, making early detection of the disease extremely important.

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Fall Webworm Spins Its Way To Attention

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Photo of fall webworms form a tent on a tree at Kohler-Andrae State Park in September 2025.

Fall webworms form a tent on a tree at Kohler-Andrae State Park in September 2025. / Photo Credit: Wisconsin DNR

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

The native insect known as fall webworm (Hyphantria cunea) has been generating calls and emails from curious property owners over the past few weeks.

The caterpillars don’t draw much attention on their own; instead, what catches the eye at this time of year are the large webs (or “tents”) that they create on the tips of tree branches.

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