Statewide Forest Health

Huge White Grubs Found In Firewood, Rotting Logs

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Closeup of large white grub larvae discovered inside logs being split for firewood.

Large white grub larvae discovered while splitting firewood. The insects are living in a piece of firewood with a lot of decay. / Photo Credit: Wisconsin DNR

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

Hermit flower beetles (Osmoderma spp.) are very large scarab beetles, sometimes called leather beetles.

Three Osmoderma species can be found in Wisconsin, though none are common. Adult beetles look big and beefy but are harmless, eating a little pollen, feeding on ripe fruit and sipping nectar and tree sap during their adult life.

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Salt Spray Damage Impacts White Pine

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A closeup of white pine needles showing browning due to damage from roadside salt spraying.

White pine with browning needles and needle tips from roadside salt spray damage. The uninjured overwintering buds at the base of the shoot will produce a new flush of growth in the spring, thereby reducing the visual appearance and health impact of the damage. / Photo Credit: Wisconsin DNR

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

An active winter weather season for snow, freezing rain and fluctuating freeze/thaw temperatures has exposed white pine along roadways to salt spray damage.

Vaporized salt spray droplets from vehicle traffic can drift into the air and settle onto vegetation, with the heaviest deposits occurring within 150 feet of a roadway.

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Jumping Worms A Threat To Gardens And Forests

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Closeup of a jumping worm on soil.

Closeup of a jumping worm (Amynthas agrestis). / Photo Credit: Wisconsin DNR

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

Invasive jumping worms are worrisome for several reasons, but here’s one of the main ones: It can be difficult to tell you even have them until they’ve already done their damage.

That makes this time of year important, because the best way to avoid damage from jumping worms, which can be substantial and long-lasting, is to prevent them from getting into your garden, yard or forestland in the first place.

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Yard Tree Owners, Send In Your Questions

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The niversity of Wisconsin-Madison Division of Extension Horticulture Program's webpage for "Ask A Gardening Question."

The University of Wisconsin-Madison Division of Extension Horticulture Program’s webpage for “Ask A Gardening Question,” the best place for homeowners to ask questions about the health of their yard trees. / Graphic Credit: UW-Madison Division of Extension

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

The Wisconsin Department of Natural Resources (DNR) has a team of Forest Health specialists that focus on problems affecting state, county and municipal forests and private forests larger than 10 acres.

But, to twist a cliché, if you can’t see the forest for the trees when it comes to your yard trees, expert help is a few clicks away.

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Oak Wilt Information Updated

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University of Wisconsin-Madison Extension online tool to help with oak wilt decisions.

A University of Wisconsin-Madison Extension online tool provides users localized information about the estimated emergence status of the two most important insects that transmit oak wilt in Wisconsin. / Graphic Credit: University of Wisconsin-Madison Extension

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

In 2025, oak wilt was detected for the first time in Hughes Township, Bayfield County, a northern Wisconsin location where oak wilt remains uncommon. There were no new county finds in 2025.

Based on the findings in 2025, the maps in the Oak Harvesting Guidelines To Reduce The Risk Of Introduction And Spread Of Oak Wilt (the oak wilt guidelines), oak wilt fact sheet and were updated. The maps in the oak wilt guidelines are good through the end of 2026.

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Stilt Grass StoryMap Updated For 2026

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Main page of the Wisconsin DNR's StoryMap on Japanese stilt grass.

The main page of the Wisconsin Department of Natural Resources’ StoryMap titled “Japanese Stilt Grass on the Coulee Experimental State Forest.” / Graphic Credit: Wisconsin DNR

By Carter Hellenbrand, DNR Invasive Plant Field Specialist, Fitchburg
Carter.Hellenbrand@wisconsin.gov

The Wisconsin Department of Natural Resources (DNR) Forest Health program has updated the Japanese stilt grass StoryMap to reflect all the work completed in 2025. The StoryMap documents the history of this invasive species on the Coulee Experimental State Forest in La Crosse County.

A StoryMap is a web-based content creation and communication tool that allows creators to share maps, apps and multimedia in the context of a narrative. Users can see an overview of Japanese stilt grass, how to identify it and what control efforts have been implemented since the plant was first detected in Wisconsin in 2020.

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Watch For Squirrel, Porcupine Damage In Spring

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Closeup of small squirrel tooth marks on a tree's mainstem.

Squirrel tooth marks are small and look like narrow scratches from which the animals have removed the tree’s bark. / Photo Credit: Wisconsin DNR

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

As winter transitions into spring, you may notice patches of tree bark that have been removed. But what did the damage?

Several animals, including squirrels and porcupines, can chew or strip bark from trees. This can occur on hardwoods and conifers, older trees and young saplings. Damage can be enough to kill branches or even the entire tree.

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Does Cold Weather Bug The Bugs?

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A map of Wisconsin showing cold temperatures on Jan. 25, 2026.

Cold temperatures across the state of Wisconsin on Jan. 25, 2026. / Graphic Credit: National Weather Service

By River Mathieu, DNR Forest Health Specialist, Fitchburg
River.Mathieu@wisconsin.gov or 608-772-2758

Wisconsin experienced a polar vortex in late January 2026, and temperatures got chilly throughout the state, even reaching close to -40⁰ F in some places! Although it has warmed up, the cold weather is still fresh in everyone’s minds, leaving insect and forest lovers alike wondering how insects survive temperatures that cold.

The Wisconsin Department of Natural Resources Forest Health staff has received several questions over the past month about how insects survive cold weather in winter and whether the January temperatures were cold enough to kill insect pests.

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Protect Valuable Ash Trees Against Emerald Ash Borer

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An ash tree in Oshkosh shows damage from woodpeckers feeding on emerald ash borer larvae beneath the bark.

An ash tree next to a walking trail in Oshkosh has been damaged by woodpeckers feeding on emerald ash borer larvae beneath the bark. / Photo Credit: Wisconsin DNR

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

Property owners with healthy, valuable ash trees are encouraged to treat them with insecticide this spring to protect against emerald ash borer (EAB).

The invasive pest is currently the most damaging threat to trees in Wisconsin, killing more than 99% of the ash trees it infests.

Woodpecker damage during the winter is often the first sign that an ash tree is infested. The birds remove pieces of bark while feeding on EAB larvae inside the tree. Insecticide treatment of infested ash trees is more likely to be successful if the trees have low or moderate levels of woodpecker damage.

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Wisconsin’s Urban Forestry Council 2025 Biennial Report Published

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By Jenn Janness, Urban Forestry Council Liaison
Jennipher.Janness@wisconsin.gov or 920-809-9330

2025 report coverThe purpose of the Wisconsin Urban Forestry Council is to advise the state forester and the Wisconsin DNR on the best ways to preserve, protect, expand and improve Wisconsin’s urban and community forest resources. Members are appointed by the DNR Secretary and represent a wide array of stakeholders, including municipal and utility foresters, medical and higher education professionals, nursery and green industry staff, environmental groups, public works and parks staff, organizations such as the Wisconsin Arborist Association (WAA), the Urban Wood Network Wisconsin, the League of Wisconsin Municipalities and government agencies such as WisDOT and DATCP. Continue reading “Wisconsin’s Urban Forestry Council 2025 Biennial Report Published” →