Forest Health News

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

Posted on by akabelowsky

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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Forest Health Staffers Hit The Airwaves

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Photo of Mike Hillstrom, who became the Wisconsin Department of Natural Resources Invasive Forest Pest Coordinator on Sept. 9, 2024.

Mike Hillstrom became the Wisconsin Department of Natural Resources Invasive Forest Pest Coordinator on Sept. 9, 2024. / Photo Credit: Wisconsin DNR

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

Mike Hillstrom and Bill McNee, members of the Wisconsin Department of Natural Resources’ Forest Health team, made notable radio appearances during November.

Hillstrom, the DNR’s invasive forest pest coordinator, appeared on Wisconsin Public Radio to discuss the invasive pest hemlock woolly adelgid (HWA). The insect has not yet established a presence in Wisconsin.

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Arbor Day Seedling Orders Open To Fourth-graders

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By Wisconsin DNR

A worker plants a red pine seedling provided by the Wisconsin Department of Natural Resources.

A worker plants a red pine seedling provided by the Wisconsin Department of Natural Resources. / Photo Credit: Wisconsin DNR

The Wisconsin Department of Natural Resources (DNR) is offering free tree seedlings to every fourth-grade student in Wisconsin as part of its annual Arbor Day tree planting program.

Wisconsin fourth-grade principals, teachers and homeschoolers can now place seedling orders and coordinate delivery by completing the 2026 Arbor Day application by March 16, 2026.

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Increased Tree Mortality Seen As Spongy Moth Outbreak Ends

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Mature spongy moth larva on a tree at Potawatomi State Park in Door County, July 2025.

Mature spongy moth larva on a tree at Potawatomi State Park in Door County, July 2025. / Photo Credit: Wisconsin DNR

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

Wisconsin’s recent period of high spongy moth populations (an “outbreak”) came to an end in 2025, as the remaining known hotspots were aerially sprayed or naturally collapsed. Only a handful of large larvae were observed or reported by property owners.

Spongy moth populations are likely to be low across the state for at least the next few years. However, it is possible that some sites may experience a population increase before then, if local weather conditions are favorable for the insect.

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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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Beware Of Invasive Plants In Your Holiday Décor

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The berries of round leaf bittersweet grow in clusters at each leaf axil and are beautiful, but this highly invasive plant makes it unsuitable for use in your fall decorations.

The berries of round leaf bittersweet (Celastrus orbiculatus) grow in clusters at each leaf axil and are beautiful, but this highly invasive plant makes it unsuitable for use in your fall decorations. / Photo Credit: Chris Evans, University of Illinois, Bugwood.org

By Wisconsin DNR

With the holiday season drawing near, it’s time for the Wisconsin Department of Natural Resources (DNR) to remind home crafters to be wary of using invasive plants in fall and winter decorations.

While holiday decorations made from natural materials can be beautiful, some wreaths and other home decorations may contain invasive species.

A quick Google or Pinterest search for décor ideas brings up a slew of orange-tinged images: pumpkins, leaves, pinecones and pretty fall foliage — sometimes boasting small, red-orange berries. While you can safely cloak your home in most of these items, avoid the one with the red-orange berries, as it likely comes from the non-native, woody vine called round leaf bittersweet (Celastrus orbiculatus, previously known as Oriental bittersweet).

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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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