Southern WI Forest Health

Phomopsis, Black Knot Easily Found In Winter

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Phomopsis galls are found on branches of a northern red oak.

This northern red oak has many large Phomopsis galls. / Photo Credit: Wisconsin DNR

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

Winter is a great time to admire the structure of trees. When they are without leaves, you can see how the branches are arranged, how large or small the branches are, and if they are fairly straight or contorted. You might also notice some swellings or growths on those branches.

Two types that can really make a statement are Phomopsis and black knot.

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Hemlock Borer Attacks Stressed Hemlock

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Closeup photo of a hemlock borer larva feeding inside channels in a hemlock tree.

A hemlock borer larva inside channels in a hemlock tree. / Photo Credit: Steven Katovich, Bugwood.org

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

Woodpeckers are often the first to know that a hemlock tree is being attacked by hemlock borer.

Woodpeckers will flake off the outer layers of bark to get at the tasty hemlock borer larvae under the bark, leaving the tree with a reddish hue that, once you’ve seen it, is unmistakable. The woodpecker damage quickly makes it obvious that the tree was fully infested from top to bottom by hemlock borer.

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Shively, McNee To Make Public Appearances

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Tim Shively, the Wisconsin Department of Natural Resources Forest Health specialist for the West Central zone.

Tim Shively, the Wisconsin Department of Natural Resources Forest Health specialist for the West Central zone. / Photo Credit: Wisconsin DNR

By Art Kabelowsky, DNR Outreach and Communications, Fitchburg
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167

Tim Shively, the Wisconsin Department of Natural Resources (DNR) Forest Health specialist for West Central Wisconsin, will give a presentation titled “Forest Health for Everyone” at a meeting of the Juneau County Men’s Shed at 10 a.m. Tuesday, Jan. 27, in Mauston.

The event is part of a program put on by the Aging and Disability Resource Center of Eagle Country, and will take place at W4890 County Hwy. N, Mauston. It is open to the public. Continue reading “Shively, McNee To Make Public Appearances” →

White Pine Blister Rust Can Devastate Young Stands

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

A close-up photo of a white pine blister rust canker as seen on a young white pine tree.

A white pine blister rust canker as seen on a young white pine tree. / Photo Credit: Wisconsin DNR

Eastern white pine (Pinus strobus) has historically held great ecological, cultural and economic value throughout Wisconsin, a tradition which continues today. For more than 100 years, however, it has been threatened by a non-native, invasive fungal pathogen called Cronartium ribicola, or white pine blister rust (WPBR).

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Impacts Of Winter Weather On Trees

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

A stand of pines shows heavy damage from an ice storm in April 2025.

A stand of pines shows heavy damage from an ice storm in April 2025. / Photo Credit: Wisconsin DNR

Winter damage can significantly impact the health of trees. Keeping trees healthy through the fall is important for reducing winter stress. Provide water as needed to trees until the leaves start falling (for deciduous trees) or until the ground starts freezing (for conifers).

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DNR, DATCP Teams Exemplify Interagency Teamwork

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By Art Kabelowsky, DNR Outreach and Communications
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167

Wisconsin Department of Natural Resources Forest Health team leader Becky Gray and Department of Agriculture, Trade and Consumer Protection Pest Survey and Control Section manager Renee Pinski appear before the Natural Resources Board to discuss tree and forest health issues on Nov. 13, 2025.

Wisconsin Department of Natural Resources Forest Health team leader Becky Gray (left) and Department of Agriculture, Trade and Consumer Protection Pest Survey and Control Section manager Renee Pinski appear before the Natural Resources Board to discuss tree and forest health issues on Nov. 13, 2025. / Photo Credit: Wisconsin DNR

The spirit of interagency communication was on display during a joint meeting of the Wisconsin Natural Resources Board (NRB) and the Wisconsin Board of Agriculture, Trade and Consumer Protection (Ag Board) on Nov. 13.

The seven-member NRB is the governing body of the Wisconsin Department of Natural Resources (DNR); the nine-member Ag Board governs the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP). Each board sets policies and rules to be followed and enforced by its respective agencies. Members of both boards are appointed by the governor and confirmed by the Wisconsin State Senate.

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Watch For Woodpecker Damage On Ash Trees

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Woodpecker flecking on the bark of a dying ash tree is visible at Winnebago County Community Park in Oshkosh.

Woodpecker flecking on the bark of a dying ash tree is visible at Winnebago County Community Park in Oshkosh. Flecking occurs when the birds peck away at the trees to feed on emerald ash borer larvae beneath the bark. / Photo Credit: Wisconsin DNR

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

The Wisconsin Department of Natural Resources (DNR) encourages property owners to watch for woodpecker damage to their ash trees this winter.

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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Report Invasive Hemlock Insects This Winter

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Small, white hemlock woolly adelgid eggs found on the needles of a tree in Bastian, Virginia, in 2017.

Small, white hemlock woolly adelgid eggs are found on the needles of a tree in Bastian, Virginia, in 2017. / Photo Credit: Bill McNee, Wisconsin DNR

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

Hemlock woolly adelgid (HWA) looms as a major threat to Wisconsin’s hemlock trees. As the infestation of these invasive, aphid-like insects spreads in Michigan and other states in the eastern United States, Wisconsin is preparing to respond when it arrives.

HWA is most evident in winter and spring as fluffy, white, woolly balls that are present at the base of hemlock needles. These fluffy, waxy balls cover adult female adelgids and eggs.

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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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Did You Know? Facts About Pine Webworm

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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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