Statewide Forest Health

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” →

Golden Oyster Mushrooms Aren’t Friends To Native Fungi

Posted on by akabelowsky
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.

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Keep An Eye Out For Beech Leaf Disease

Posted on by akabelowsky
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.

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Common HRD Treatment No Longer Available

Posted on by akabelowsky
A pine stump with a Heterobasidion root disease fruit body with old brown growth in the center and new, bright white growth along the edges.

A Heterobasidion root disease (HRD) fruit body with new white growth observed in the fall. Photo: Wisconsin DNR

The Wisconsin Department of Natural Resources Forest Health Newsletter reports that the fungicide Rotstop® C is no longer available in North America.

Rostop® C is commonly used to protect against Heterobasidion root disease (HRD) during conifer timber harvests. It has been discontinued in the North American market. Cellu-Treat® is now the only registered and available to prevent HRD in Wisconsin. Check out the article from DNR Forest Health for more detail.

As always, remember to report your pesticide use when applying these or any other pesticides on property in the MFL Certified Group. You can use the online reporting form or send the required information to MFLForestCertification@wisconsin.gov.

Maple Petiole Borer Sawfly Causing Leaf Drop

Posted on by akabelowsky
A closeup display photo showing prematurely fallen sugar maple leaves that have a normal appearance, except for characteristic darkened petiole stubs caused from feeding damage of the maple petiole borer.

Prematurely fallen sugar maple leaves with normal appearance except for characteristic darkened petiole stubs caused from feeding damage of the maple petiole borer. / Photo Credit: Paul Cigan, Wisconsin DNR

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

Fallen maple leaves have been observed under Wisconsin maple trees since late May.

The fallen leaves are typically of normal shape, size and color, but have a darkened petiole stub (i.e., leaf stem) remaining. A closer examination of the petiole may reveal a hollow feeding tunnel containing tiny larvae of the insect responsible for the damage inside: the maple petiole borer.

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Anthracnose Infecting Hardwood Leaves

Posted on by akabelowsky
Photo of ash leaves infected with anthracnose.

Ash leaves infected with anthracnose. / Photo Credit: Wisconsin DNR

By Michael Hillstrom, DNR Forest Health Specialist
Michael.Hillstrom@wisconsin.gov
and Abby Krause, DNR Urban Forestry Coordinator
Abigail.Krause@wisconsin.gov

Anthracnose is a common disease of hardwood trees during cool, wet spring seasons. Some parts of Wisconsin have been cooler and wetter than others this spring, so anthracnose damage may be patchy.

Ash, maple, white oak, sycamore and walnut are the most impacted tree species. Each species has its own species of anthracnose that infects it, but if weather conditions are right, then we tend to see damage on multiple species.

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DNR Debuts Fact Sheet On White Grubs

Posted on by akabelowsky
Closeup photo showing a white grub in topsoil, feeding on a root.

A white grub feeds on a root. / Robert L. Anderson, USDA Forest Service, Bugwood.org

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

White grubs, the larvae of Wisconsin’s native May/June beetles (Phyllophaga spp.), can cause significant damage to forest plantings.

To help those who plan to plant seedlings and saplings, the Wisconsin Department of Natural Resources’ (DNR) Forest Health team has produced a fact sheet on white grubs, aimed specifically at forest plantings.

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Wild Cucumber Will Catch Your Attention

Posted on by akabelowsky
A photo showing star-shaped leaves, pale flowers and cucumber fruit, all characteristics of wild cucumber.

Star-shaped leaves, pale flowers and cucumber fruit, all characteristics of wild cucumber. / Photo Credit: Bugwood.org

By the Wisconsin Department of Natural Resources

Plants that are pokey, viny or quick to spread across the landscape sometimes seem alarming when you discover them in your backyard or woods, or even when you spot them along the highway.

Wild cucumber has all these characteristics, and its growth rate has been quite prolific in some parts of Wisconsin again this year. But all of this is not as ominous as it seems.

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Anthracnose Infecting Hardwood Leaves

Posted on by janness

By Michael Hillstrom, DNR Forest Health Specialist; Michael.Hillstrom@wisconsin.gov
and Abby Krause, DNR Urban Forestry Coordinator; Abigail.Krause@wisconsin.gov

Oak leaves infected with anthracnose.

Anthracnose is a common disease of hardwood trees during cool, wet spring seasons. Some parts of Wisconsin have been cooler and wetter than others this spring, so anthracnose damage may be patchy.

Ash, maple, white oak, sycamore and walnut are the most commonly impacted tree species. Each species has its own species of anthracnose that infects it, but if weather conditions are right, then we tend to see damage on multiple species. Continue reading “Anthracnose Infecting Hardwood Leaves” →

Spongy Moth Population In Decline

Posted on by akabelowsky
A photo of a tree trunk showing spongy moth caterpillars killed by nucleopolyhedrosis virus (NPV) hang in an inverted “V” orientation; caterpillars killed by the fungus Entomophaga maimaiga hang vertically.

Spongy moth caterpillars killed by nucleopolyhedrosis virus (NPV) hang in an inverted “V” orientation; caterpillars killed by the fungus Entomophaga maimaiga hang vertically. / Photo Credit: Wisconsin DNR

By Michael Hillstrom, Wisconsin DNR Forest Health Specialist
Michael.Hillstrom@wisconsin.gov; 608-513-7690

Spongy moth caterpillars began hatching at the end of April in 2025 and are now actively feeding on leaves. In most Wisconsin locations, though, the population will not be as high as it has been in the last few years.

Wisconsin has had the largest outbreak in state history over the past few years. Fortunately, the outbreak collapsed in many areas of the state in 2024. The wet spring weather in April and May of 2024 allowed a fungus and a virus that infects spongy moth caterpillars to cause heavy mortality. Although some hot spots still exist in south central and northeast Wisconsin, we expect those populations to decline in 2025.

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