Forest Health News

Pine False Webworm Uncommon In Wisconsin

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Messy webbing filled with frass (droppings) and pieces of needles are signs of pine false webworm feeding on this young white pine. The arrow points to a pine false webworm larvae. / Photo Credit: Wisconsin DNR

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

Pine false webworm (Acantholyda erythrocephala) is not a very common insect in Wisconsin, though it is present. They prefer to feed on white pine in Wisconsin, though reference materials say they will also feed on red pine, jack pine and Scotch pine.

Damage was reported as “minor” in the central part of the state from 1953 to 1961. Later, in 1995, 1997, 2002, 2004 and 2006, it was once again observed as a minor pest feeding on red or white pine in the central part of the state, particularly Portage, Waupaca and Waushara counties. In 2024 and again this year, a few scattered young white pine were observed being significantly defoliated in Oneida and Vilas counties.

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Japanese Beetle Populations Still Building In The North

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Beetles feeding on a basswood leaf.

Japanese beetles defoliating a basswood leaf. / Photo Credit: Wisconsin DNR

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

The Japanese beetle (Popillia japonica) is an invasive insect that feeds on many plant species. The adult beetles “skeletonize” leaves by eating the material between the veins.

Adult Japanese beetles feed on the flowers and leaves of more than 300 plant species, including trees, shrubs and herbaceous plants. Forest trees can be defoliated, with open-grown or edge trees suffering the highest defoliation rates.

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Spruce Budworm Hits Hemlock And Tamarack

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Closeup of hemlock branches showing missing and damaged needles.

Hemlock branches show missing needles, and needles with feeding damage, as the result of spruce budworm infestation. / Photo Credit: Wisconsin DNR

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

Spruce budworms are finished feeding for the year, but the damage is still being noticed. That’s especially true in areas where defoliation was severe, such as northeastern Oneida County and southeastern Vilas County.

Spruce budworm prefers to feed on balsam fir and spruce, but in areas with very high populations and severe defoliation, they will also feed on hemlock and tamarack.

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Tamaracks Busy Refoliating After Larch Casebearer Defoliation

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Wide view of stand of trees

Tamarack trees showing the effect of larch casebearer defoliation. / Photo Credit: Wisconsin DNR

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

Earlier this spring, scattered areas of tamarack in North Central and Northeastern Wisconsin showed tan or light brown foliage. Sometimes that is due to frost, but this year it was the work of an insect called larch casebearer.

As the foliage started to expand this spring, the larch casebearer became active and began to feed. The tiny caterpillars mine out the needles of tamarack and use them as “cases” to protect themselves, thus their name.

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Forest Health Staffers Plan Public Appearances

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Two DNR workers discuss tree issues in the forest.

Alex Hornung, Wisconsin DNR Forest Health specialist for Central Wisconsin, discusses the tree disease phomopsis with Chief Forester Heather Berklund during a site visit near Minocqua in July 2026. / Photo Credit: Wisconsin DNR

By Art Kabelowsky, DNR Forest Health Communications, Fitchburg;
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167

Alex Hornung, the Wisconsin Department of Natural Resources Forest Health Specialist for Central Wisconsin, will discuss oak wilt biology at a workshop this month.

Hornung will take part in a Wisconsin Forestry Center/Wisconsin Natural Resources Foundation workshop on oak wilt biology and management, focused on information for landowners and the public. The discussion will take place from 1 to 3:30 p.m. Tuesday, Aug. 18, at Schmeeckle Reserve, 2419 N. Point Drive, Stevens Point. She will be joined by Dr. Holly Petrillo, Professor of Forestry at the University of Wisconsin-Stevens Point.

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First Populations Of Invasive Pale Swallow-wort Confirmed In Wisconsin

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Closeup of pale swallow-wort flower cluster.

Pale swallow-wort flowers along the stem at the leaf axils. / Photo Credit: Chris Evans, University of Illinois, Bugwood.org

By Mackenzie Manicki, DNR Natural Resources Research Scientist

The Wisconsin Department of Natural Resources has confirmed that the state’s first populations of the invasive vine pale swallow-wort (Vincetoxicum rossicum) have been found.

The populations were first detected in Oconto and Shawano counties, within the outskirts of Krakow along the shared county line.

These are the first known populations in the state, making rapid response efforts critical in preventing the establishment of this species in Wisconsin.

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Public Hearing On Invasive Species Regulations Set

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A wide-angle photo of an infestation of Japanese stilt grass in a forest.

A field at the Coulee Experimental Forest near La Crosse is infested by Japanese stilt grass. / Photo Credit: Wisconsin DNR

By Jenn Janness, DNR Urban Forestry Communications

The Wisconsin Department of Natural Resources will hold a virtual public hearing on a permanent rule to revise Ch. NR 40, relating to changes to invasive species regulations.

Meeting details:

  • Date: Aug. 5, 2026
  • Time: 5 p.m.
  • Online: Join via Microsoft Teams
  • Phone: Join by calling 608-571-2209 and entering phone conference ID 496 793 478#

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Forest Health Team Debuts Two New Fact Sheets

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An image of the front page of a DNR fact sheet.

The front page of the Wisconsin DNR’s new Forest Health Fact Sheet on oak decline. / Graphic Credit: Wisconsin DNR

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

The Wisconsin Department of Natural Resources Forest Health team has published two new fact sheets, bringing the total count of its fact sheet offerings to 26.

The new fact sheets:

  • Fall Webworm: DNR Publication FR-622u discusses basic information on the biology of the insect (Hyphantria cunea), its life cycle, potential lookalike caterpillars and management options.
  • Oak Decline: DNR Publication FR-622v covers the tricky topic of oak decline, which is not caused by one distinct forest pest or problem but instead is the result of multiple factors — some predisposing, some inciting and some contributing — that work in combination to cause decline.

The fact sheets are designed in full color, with photos, and are meant to be printed out for reference or to carry into the field. They can also be viewed online. They can be printed on standard letter-sized paper. Most fact sheets are two pages, meant for two-sided printing; a few are four-page documents.

A complete directory of links to all DNR Forest Health fact sheets is available online.

Forest Health Staffers Plan Appearances

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Two workers inspecting a tree's leaves.

Mike Hillstrom and Linda Williams of the Wisconsin Department of Natural Resources Forest Health team look over a tree during a walking tour put on by the Cambridge Tree Project on July 10, 2025. / Photo Credit: Wisconsin DNR

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

Mike Hillstrom, Invasive Forest Pest Coordinator for the Wisconsin DNR Forest Health Team, will make a presentation on forest health to the Heartland National Christmas Tree Organizations Convention, scheduled for Friday, Aug. 7, at Hann’s Christmas Farm, 848 Tipperary Road, Oregon, WI 53575.

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Oak Decline May Continue In 2026

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A wide view of declining oak trees following spongy moth defoliation and drought.

Oak trees with thin canopies experiencing decline following spongy moth defoliation and drought in the prior few years. / Photo Credit: Wisconsin DNR

By River Mathieu, DNR Forest Health Specialist, Fitchburg
River.Mathieu@wisconsin.gov

Oak decline is a complicated forest health issue impacting oak forests in Wisconsin.

In the past few years, oak decline has been recorded in several regions of Wisconsin, primarily linked to spongy moth defoliation and drought conditions that occurred from 2022-2024.

As the summer months of 2026 continue to unfold, oak decline may continue in areas previously impacted by spongy moth and drought.

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