Statewide Forest Health

Sawflies On Jack Pine Are Neodiprion Maurus

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Photo showing five Neodiprion maurus larvae feeding on jack pine needles.

Neodiprion maurus larvae, feeding on jack pine, are gregarious. Can you spot all five larvae? / Photo Credit: Wisconsin DNR

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

In mid-July, a few sawfly larvae were found feeding on jack pine in northern Vilas County. After delving into associated literature and reaching out to a sawfly researcher at the University of Kentucky, the sawflies were identified as Neodiprion maurus. There is no official common name for this insect; it is generally referred to as “a sawfly on jack pine.”

These sawflies are gregarious and feed in groups on older needles, doing relatively minimal damage. They are often referred to as “rare” and have been found in Michigan, Minnesota and Wisconsin, as well as Alberta, Manitoba and Saskatchewan in Canada.

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Pink Striped Oakworm Seen Feeding On Red Oaks

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Closeup photo showing young pink striped oakworm caterpillars feed gregariously on northern red oak leaves.

Young pink striped oakworm caterpillars feed gregariously on northern red oak leaves. / Photo Credit: Wisconsin DNR

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

Young larvae of the pink striped oakworm (Anisota virginiensis) have been observed feeding gregariously on northern red oak leaves in Vilas County. Northern red oak is their preferred host, but they can feed on other oaks.

Young caterpillars start life with a shiny black head capsule, but older larvae develop an orange head. Their pinkish body coloration develops as they get older, as well; young caterpillars are dark green in color.

Pink striped oakworm has several fly parasitoids, along with a couple of wasp parasitoids. Populations of pink striped oakworm in Wisconsin don’t usually grow too large or cause problems.

 

Northern Pitch Twig Moth Creates Pitch Blisters On Jack Pine

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Closeup photo showing that hollow pitch blisters get darker with age and may resemble cones until closer examination.

Hollow pitch blisters get darker with age and may resemble cones until closer examination. / Photo Credit: Wisconsin DNR

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

Northern pitch twig moth (Petrova alhicapitana) is also called the pitch nodule maker or pitch blister moth.

It feeds on branches and twigs of young jack pine and scotch pine, causing a hollow blister of gooey pitch to form around the larvae as it feeds at the base of a lateral branch. It prefers trees that are 20 feet tall or smaller, although it can attack older trees.

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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.”)

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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.

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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.

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Common HRD Treatment No Longer Available

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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

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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

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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

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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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