Month: August 2025

Invasive Plant Japanese Stiltgrass Detected In Rock County

Posted on by akabelowsky
A wide-angle photo showing a mat of Japanese stiltgrass growing in Rock County, Wisconsin, in July 2025.

A mat of Japanese stiltgrass growing in Rock County, Wisconsin, in July 2025. / Photo Credit: John Zaborsky, University of Wisconsin-Madison Renz Weed Science Lab

By Wisconsin DNR

The harmful invasive plant Japanese stiltgrass (Microstegium vimineum) has been detected in a private woodland near Beloit in Rock County, according to a blog post made Monday by the University of Wisconsin-Madison Extension.

It is the second detection of the non-native annual grass in Wisconsin. The first took place in 2020, inside the Coulee Experimental Forest in La Crosse County. The Wisconsin Department of Natural Resources  (DNR) has been working to eradicate that population.

Continue reading “Invasive Plant Japanese Stiltgrass Detected In Rock County” →

Native Sawyer Beetles Resemble Asian Longhorned Beetle

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An adult Asian longhorned beetle, left, and an adult whitespotted sawyer beetle, right. The arrow shows the white spot at the top of the whitespotted sawyer beetle’s wing covers, indicating it’s the native beetle and not Asian longhorned beetle. / Photo Credits: Left, Bugwood.org; right, Wisconsin DNR

Two closeup photos show the similarities and differences between an adult Asian longhorned beetle, left, with spots all over its back and striped antennae; and an adult whitespotted sawyer beetle, right, with one white spot beneath its head and between its wings.

By Michael Hillstrom, DNR Invasive Forest Pest Coordinator
Michael.Hillstrom@wisconsin.gov

More than 300 species of longhorn beetles inhabit the Midwest. The Wisconsin Department of Natural Resources (DNR) posted about one species, the invasive Asian longhorned beetle (ALB), on social media in early July.

Forest Health staff received many photos of potential ALB as a result. Fortunately, none of the photos were of ALB – which has yet to be detected in Wisconsin.

By far, the most common insect seen in the submitted photographs was a native longhorn species called the whitespotted sawyer beetle (Monochamus scutellatus), also known as a pine sawyer beetle.

Continue reading “Native Sawyer Beetles Resemble Asian Longhorned Beetle” →

Monitor Your Trees For Spongy Moth-Related Decline And Mortality

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A photo taken June 20, 2025, shows dead and dying oaks near Whitewater Lake in Walworth County, following a period of defoliation and summer drought.

A photo taken June 20, 2025, shows dead and dying oaks near Whitewater Lake in Walworth County, following a period of defoliation and summer drought. / Photo Credit: Wisconsin DNR

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

Property owners are encouraged to monitor their trees for signs of decline and mortality, as the last few years have been marked by drought and spongy moth defoliation.

Landowners who have oak, birch, crabapple, aspen, willow, tamarack and basswood (linden) trees should be particularly watchful, because the caterpillars of this invasive insect prefer these species. Many other tree species are not preferred by the caterpillars and are less likely to be heavily defoliated, but are more likely to die if heavy defoliation should happen.

This article focuses on oak impacts.

The 2021-24 spongy moth outbreak has now collapsed statewide; no defoliation has been observed as of late July 2025. Only a few reports of single caterpillars were received by Wisconsin DNR Forest Health staff. (Note: Parts of Wisconsin may be experiencing a continuing outbreak of different caterpillars known as “oak leafroller” and “larch casebearer.”)

Continue reading “Monitor Your Trees For Spongy Moth-Related Decline And Mortality” →

Avoid Ash Trees When Placing Deer Stands

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Photo showing a Wisconsin hunter climbing into his tree stand.

A Wisconsin hunter climbs into his tree stand. The Wisconsin Department of Natural Resources urges hunters to avoid placing their stands on or near ash trees because the trees may experience breakage of stems or branches due to damage from the emerald ash borer. / Photo Credit: Wisconsin DNR

By Wisconsin DNR

It’s time for deer hunters to begin scouting properties to identify potential locations for their deer stands this hunting season.

The Wisconsin Department of Natural Resources (DNR) cautions hunters to avoid placing deer stands in or near ash trees – a practice that presents a clear safety hazard.

Most ash trees in the southern two-thirds of Wisconsin are dead or dying due to the emerald ash borer (EAB), and infestations in the northern part of the state are rapidly expanding. Some areas already experience decline and mortality of ash trees. EAB has been confirmed present in all 72 Wisconsin counties, and unreported infestations are also likely to be present.

Continue reading “Avoid Ash Trees When Placing Deer Stands” →

Golden Oyster Mushrooms Aren’t Friends To Native Fungi

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Closeup photo showing golden oyster mushrooms growing on a dead American elm tree in Green County in June 2025.

Golden oyster mushrooms grow on a dead American elm tree in Green County in June 2025. / Photo Credit: Wisconsin DNR

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

Golden oyster mushrooms (Pleurotus citrinopileatus) have eye-catching bright-yellow caps with branch-like white gills. Recently, more people have been noticing these gorgeous-looking clusters of mushrooms growing on trees in Wisconsin, especially in southern Wisconsin.

These mushrooms, prized for culinary delicacy, are native to eastern Asia. However, they are found in forests throughout the Midwest and northeastern United States, including Wisconsin.

Continue reading “Golden Oyster Mushrooms Aren’t Friends To Native Fungi” →

Herbicide Damage To Trees? Always Read The Label

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Closeup photo showing active ingredients listed on the front label of pesticide containers. The complete label, including instructions, may be on the front or back of the bottle and will require opening to read.

Active ingredients are listed on the front of pesticide containers (yellow arrow above). The complete label, including instructions, may be on the front or back of the bottle and will require opening to read (blue arrow above). / Photo Credit: Wisconsin DNR

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

This is your reminder to always read pesticide labels, even if you think the product you are using is the same product you’ve always used.

Do you always check the active ingredients listed on the front of pesticide containers – and read instructions on the use of the product – every time you buy a new container of pesticide? It has become more important than ever to do so.

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Keep An Eye Out For Beech Leaf Disease

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Photo showing symptomatic striping from beech leaf disease, seen from under the canopy.

Symptomatic striping from beech leaf disease, seen from under the canopy. / Photo Credit: Kyoko Scanlon, Wisconsin DNR; taken in Cleveland, Ohio

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

Forest owners and land managers should look for beech leaf disease (BLD), a destructive beech tree disease in the United States, this summer.

Although it has not yet been found in Wisconsin, recent discoveries of the disease in Michigan and other nearby states highlight the continued importance of monitoring BLD’s expansion. There is potential for BLD to move into Wisconsin, as the eastern portion of the state overlaps with the native range of American beech.

Continue reading “Keep An Eye Out For Beech Leaf Disease” →

Japanese Beetle Defoliates Some Forest Trees In The North

Posted on by akabelowsky
Closeup photo of Japanese beetles defoliating a basswood leaf

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

By Linda Williams, DNR Forest Health Specialist
Linda.Williams@wisconsin.gov or 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.

Japanese beetles favor birch, mountain ash and basswood (linden) trees, but they have also been observed feeding on the leaves of young oaks.

Continue reading “Japanese Beetle Defoliates Some Forest Trees In The North” →

Viburnum Leaf Beetle Appearing In Forests

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

Closeup photo showing small brown adult viburnum leaf beetles causing typical defoliation on a leaf.

Small brown adult viburnum leaf beetles cause typical defoliation on a leaf. / Photo Credit: Wisconsin DNR

Viburnum leaf beetle (Pyrrhalta viburni) is a relatively new invasive insect in Wisconsin. It originated in Eurasia and was first identified in Wisconsin in 2009.

Adults and larvae feed on the leaves of viburnums and can cause mortality after a few years of repeated defoliation. Feeding causes characteristic holes in the leaves. Beetle numbers can be very high on a single plant.

Viburnum leaf beetle has been observed defoliating native viburnum species including American Highbush Cranberry (Viburnum opulus var. americana) and Mapleleaf Viburnum (Viburnum acerifolium) in forest stands in Iron County and more recently in Oneida County.

Continue reading “Viburnum Leaf Beetle Appearing In Forests” →

Locust Sawfly Defoliation Found In Oneida County

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

Closeup photo showing four locust sawfly larvae feeding on bristly locust leaves.

Four locust sawfly larvae feed on bristly locust leaves. / Photo credit: Wisconsin DNR

In early July, black locust and bristly locust in several areas of Oneida County were severely defoliated by locust sawfly.

Affected trees and shrubs have now produced additional leaves, making the defoliation less obvious. Damage was not noted in other areas of the state.

The sawflies are finished feeding, so no control is necessary.