Insect

Green, Sawyer Counties Added To Spongy Moth Quarantine

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Map of Wisconsin showing counties in yellow quarantine for spongy moth.

The updated map of spongy moth quarantined counties in Wisconsin, showing the April 15 addition of Green and Sawyer counties to the quarantined list. / Map Credit: Wisconsin DNR

By Wisconsin DNR

Green and Sawyer counties have become the latest additions to Wisconsin’s spongy moth quarantine, joining most eastern and central Wisconsin counties already considered to be infested by the invasive insect.

The announcement was made April 15 by the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP), based on trapping data collected last year.

Continue reading “Green, Sawyer Counties Added To Spongy Moth Quarantine” →

Cooperative Hemlock Woolly Adelgid Trapping Effort Begins

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A 3-D printed trap used to collect hemlock woolly adelgid DNA. / Photo Credit: Wisconsin DNR

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

This spring, the Wisconsin Department of Natural Resources (DNR) is collaborating with the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) to set traps to detect the invasive insect hemlock woolly adelgid (Adelges tsugae; HWA).

The project, funded by the Wisconsin Specialty Crop Block Grant Program, calls for traps to be set to detect the invasive insect. No detection of HWA has been made to date in Wisconsin forests. Continue reading “Cooperative Hemlock Woolly Adelgid Trapping Effort Begins” →

Take Precautions to Prevent Tick Bites

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An adult deer tick looks for a spot to attach. / Photo Credit: Wisconsin DNR

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

Adult blacklegged (deer) ticks are already active this year, as of March 2026. The adults start looking for a host as soon as it warms up to around 40 degrees Fahrenheit.

In Wisconsin, between 20-60 percent of adult ticks are infected with the bacteria that causes Lyme disease. However, the risk of getting Lyme disease is higher with bites from nymphal ticks, which are most abundant in June and July, because they are so tiny and difficult to find. While only 10-28 percent of nymphs are infected with the Lyme disease bacteria in Wisconsin, rapid removal of a tick can reduce the risk of infection because it takes at least 24 hours for the Lyme bacteria to spread.

Continue reading “Take Precautions to Prevent Tick Bites” →

Aerial Spraying For Spongy Moth Planned at Perrot State Park

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A map showing the area to be covered by a 2026 aerial spray for spongy moth caterpillar control at Perrot State Park.

A map showing the 2026 spongy moth caterpillar aerial spraying area planned for Perrot State Park in Trempealeau County. / Map Credit: Wisconsin Department of Agriculture, Trade and Consumer Protection.

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

This spring, a portion of Perrot State Park in Trempealeau County will be aerially treated for spongy moth with “Foray” bacterial insecticide, containing Bacillus thuringiensis var. kurstaki.

A reproducing population of the leaf-eating caterpillar was detected in the park last fall, leading to the decision to conduct aerial spraying in 2026.

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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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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.

Continue reading “Does Cold Weather Bug The Bugs?” →

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 Sees First Recovery Of EAB Parasitoid Oobius Agrili

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A plastic pan trap for wasps is hung from a tree branch.

A yellow pan trap used for trapping Oobius agrili wasps. / Photo Credit: United States Department of Agriculture Animal and Plant Health Inspection Service

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

One small adult wasp collected by United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) staff at Riedel Redmond Nature Preserve in Mosinee (Marathon County) was recently identified as Oobius agrili.

USDA APHIS staff collected several wasp specimens in yellow pan traps and sent them to a U.S. Forest Service expert for identification. This marks the first recovery of O. agrili in Wisconsin.

Oobius agrili is an emerald ash borer (EAB) parasitoid that was first released in Wisconsin in 2011 and has been released annually since then. O. agrili parasitizes EAB eggs on the bark of ash trees, consuming the EAB larvae inside the egg. Continue reading “Wisconsin Sees First Recovery Of EAB Parasitoid Oobius Agrili” →

Now Is Time To Seek Out Spongy Moth Egg Masses

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Large spongy moth egg masses on a tree main stem.

Large egg masses are seen on a tree at the Kettle Moraine State Forest-Southern Unit in 2021. / Photo Credit: Wisconsin DNR

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

It certainly has been chilly in recent weeks, but spring is coming. When the weather warms up, the annual return of spongy moth caterpillars will begin.

The overall spongy moth population is currently low in Wisconsin. However, egg mass numbers may remain high enough to cause nuisance problems and heavy tree defoliation on individual trees or in small areas.

There’s a way for property owners to help keep the population down: Get out now to locate and properly dispose of spongy moth egg masses, which were produced by adult moths last summer. Each spongy moth egg mass contains hundreds of eggs that will hatch into hungry, leaf-eating caterpillars in the spring.

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Heterobasidion Root Disease Resources Updated

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Heterobasidion root disease fruiting bodies grow on base of tree

A tree shows fruiting bodies of Heterobasidion root disease at the base of its trunk. / Photo Credit: Wisconsin DNR

By Kyoko Scanlon, DNR Forest Pathologist
Kyoko.Scanlon@wisconsin.gov or 608-235-7532

In 2025, Heterobasidion root disease (HRD), a destructive fungal disease, continued to be found in Wisconsin counties where the disease had previously been detected. There were no new county finds in 2025.

Based on the findings in 2025, the maps in the HRD stump treatment guidelines and online viewer have been updated. The 6-mile and 25-mile buffer zone maps in the guidelines are updated annually and good through Dec. 31, 2026.

Continue reading “Heterobasidion Root Disease Resources Updated” →