Pests

Native Sawyer Beetles Resemble Asian Longhorned Beetle

Posted on by akabelowsky
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.

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Monitor Your Trees For Spongy Moth-Related Decline And Mortality

Posted on by akabelowsky
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

Posted on by akabelowsky
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.

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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.

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Viburnum Leaf Beetle Appearing In Forests

Posted on by akabelowsky

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.

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Locust Sawfly Defoliation Found In Oneida County

Posted on by akabelowsky

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.

Resources to Help Urban Foresters Set And Meet Tree Diversity Goals

Posted on by janness

By Shahla Werner, Urban Forestry Council Member and Department of Agriculture, Trade and Consumer Protection Plant Protection Section Manager

Urban foresters are increasingly aware of the importance of tree species, age and size diversity to ensure resilient tree canopy and all the associated benefits in their communities. The 20-10-5 rule, which specifies that no more than 20% of trees planted should be from one family, no more than 10% from one genus and no more than 5% from one species (including cultivars), can be helpful in setting tree diversity goals. Applying these guidelines can provide urban forests some protection against huge losses caused by invasive forest pests. Continue reading “Resources to Help Urban Foresters Set And Meet Tree Diversity Goals” →

2025 DNR Spongy Moth Spray Plans Announced

Posted on by akabelowsky
Photo showing an airplane spraying pesticide over trees at Devils Lake State Park in Sauk County to help in the control of spongy moth caterpillars.

An airplane sprays pesticide over trees at Devils Lake State Park in Sauk County to help in the control of spongy moth caterpillars. / Photo Credit: Sue Johansen, Wisconsin DNR

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

The Wisconsin Department of Natural Resources (DNR) has finalized aerial spraying plans for its 2025 Spongy Moth Suppression Program, with maps for the five selected treatment areas available online.

The treatment sites are at three state parks in Juneau, Marinette and Sauk counties that are highly valued for their recreational use. A total of 544 acres of trees will be treated with an aerial spray of “Foray” bacterial insecticide containing Bacillus thuringiensis var. kurstaki.

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La Crosse County Added To Spongy Moth Quarantine

Posted on by akabelowsky
A closeup photo of a spongy moth caterpillar consuming a leaf.

A spongy moth caterpillar consumes a leaf. / Photo Credit: Bill McNee, Wisconsin DNR

By Wisconsin Department of Natural Resources (DNR)

La Crosse County has become the latest Wisconsin location to be added to the state and federal spongy moth quarantine, joining most eastern and central Wisconsin counties already considered to be infested by the invasive insect.

The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) announced the change on April 1, based on trapping data collected last year.

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DNR Urges Spring Spongy Moth Treatment Plans

Posted on by akabelowsky
Carefully scraping spongy moth egg masses off trees and into a cup of soapy water will help to hold down caterpillar damage in 2025.

Carefully scraping spongy moth egg masses off trees and into a cup of soapy water will help to hold down caterpillar damage in 2025. / Photo Credit: Bill McNee, Wisconsin DNR

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

The Wisconsin Department of Natural Resources (DNR) encourages property owners to examine their trees for spongy moth egg masses and determine whether control measures are needed this spring.

Property owners who have oak, birch, crabapple, aspen, willow and linden (basswood) trees should be particularly watchful because the caterpillars of this invasive insect prefer these species. However, they will feed on many other kinds of trees and shrubs.

Continue reading “DNR Urges Spring Spongy Moth Treatment Plans” →