Forest Health News

Spruce Budworm Defoliation Continues

Posted on by akabelowsky

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

Closeup photo showing that webbing created by the spruce budworm caterpillar holds needles and frass and protects the caterpillar. A pupa hangs from the branch.

Webbing created by the spruce budworm caterpillar holds needles and frass and protects the caterpillar. A pupa hangs from the branch. / Photo Credit: Linda Williams, Wisconsin DNR

Although symptoms weren’t as prevalent as in 2023, this year marked yet another year of defoliation from spruce budworm.

Another severe year of defoliation causes additional stress on the trees. Even though there has been a lot of rainfall this spring, it’s still stressful for the trees to face repeated years of defoliation by spruce budworm before they begin to decline and die.

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Dropping Leaves May Indicate Oak Wilt

Posted on by akabelowsky

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

Photo showing that oak leaves that drop from a tree infected with oak wilt may be all brown or all green, or often they will have green near the base of the leaf and the outer portions will be brown or watersoaked green.

Oak leaves that drop from a tree infected with oak wilt may be all brown or all green, or often they will have green near the base of the leaf and the outer portions will be brown or watersoaked green. / Photo Credit: Linda Williams, Wisconsin DNR.

The middle of summer is the time to start watching oak trees for symptoms of oak wilt. Although symptoms show up suddenly and leaves drop quickly, symptoms can emerge anytime between now and when leaves turn color in the fall.

Trees that were wounded in the spring and became infected with the fungus that causes oak wilt will usually die that same year. In established oak wilt pockets, the fungus moves underground through grafted root systems and trees will wilt as the fungus moves into the tree.

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Tubakia Leaf Disease Affects Red Oak

Posted on by akabelowsky

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

A tree showing that lower branches are thin and have lost leaves due to Tubakia leaf spot, while leaves on its upper branches look good.

A tree showing that lower branches are thin and have lost leaves due to Tubakia leaf spot, while leaves on its upper branches look good. / Photo Credit: Linda Williams, Wisconsin DNR.

Tubakia leaf spot is a leaf disease caused by a fungus (Tubakia dryina) that typically affects the lower canopy of red oaks.

Because of all the rain that came during the spring and early summer of 2024, the fungus has started to impact some trees. Problems didn’t occur last year because the weather was too dry.

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Emerald Ash Borer Confirmed In All 72 Counties

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

Closeup photo of an adult emerald ash borer. The pest has been detected in Burnett County, making it the 72nd and final county in Wisconsin that have confirmed presence of the invasive insect.

The emerald ash borer has been detected in Burnett County, making it the 72nd and final county in Wisconsin that have confirmed presence of the invasive insect. / Photo Credit: Paul Cigan, Wisconsin DNR

Sixteen years after the Wisconsin Department of Natural Resources (DNR) first detected emerald ash borer (EAB) in Wisconsin, the invasive beetle has been found in the last county without a previous detection.

Burnett County, in northwest Wisconsin, is the 72nd and final county to have a detection of the tree-killing pest.

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Basswood Trees Short On Leaves Due To Thrips

Posted on by akabelowsky

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

Photo showing Basswood leaves that have been damaged due to the feeding of introduced basswood thrips.

Basswood leaves show damage due to the feeding of introduced basswood thrips. / Photo Credit: Linda Williams, Wisconsin DNR

For the third consecutive year, damage from introduced basswood thrips (Thrips calcaratus) is significant in some areas of northeast Wisconsin, especially Forest County.

Introduced basswood thrips are tiny, invasive insects that feed inside tree buds in early spring. The feeding causes leaves to deform when they expand, looking like they suffered frost or wind damage.

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Keep An Eye Out For Beech Leaf Disease

Posted on by akabelowsky

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

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

The disease is primarily found on American beech (Fagus grandifolia) but can also be found on ornamental species such as European, Oriental and Chinese beech (F. sylvatica, F. orientalis and F. engleriana). 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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Periodical Cicada Damage Now Visible

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

Photo of Brood XIII periodical cicadas (Magicicada spp.) resting on a tree at Big Foot Beach State Park in Lake Geneva on June 12, 2024.

Brood XIII periodical cicadas (Magicicada spp.) rest on a tree at Big Foot Beach State Park in Lake Geneva on June 12, 2024.

Scattered twig death, commonly known as “flagging,” was recently observed on several trees at Big Foot Beach State Park in Walworth County, where large numbers of 17-year Brood XIII periodical cicadas (Magicicada spp.) were present. This flagging is likely present in other localized sites in southern Wisconsin that experienced high numbers of cicada emergences.

The University of Wisconsin-Madison Insect Diagnostic Lab’s Periodical Cicadas in Wisconsin webpage has more information about the periodical cicada outbreak.

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Invasives And Imposters: Native Look-Alikes To Know

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By Erika Segerson-Mueller, DNR Invasive Plant Program Specialist, Oshkosh;
Erika.SegersonMueller@wisconsin.gov or 715-492-0391

Native plants benefit Wisconsin wildlife, pollinators and ecosystems. However, many resemble harmful invasive species, making identifying problem plants in the woods challenging.

It is important to learn a few key characteristics to unmask the imposters and correctly identify the invasive plants. With a little study and practice, you can quickly differentiate between these perplexing pairs.

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Five Years Later, Effects Of Derecho Remain

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

Over the night of July 19-20, 2019, Mother Nature carved a massive swath of destruction through northern Wisconsin.

Today, after years of hard work cleaning up after the massive derecho windstorm of ’19, local foresters, work crews and landowners have only begun to understand the breadth and depth of the damage as they process the lessons learned.

In many areas, the recovery work remains incomplete. Some of that forest damage will never receive direct attention.

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Oak Moth Outbreaks May Have Peaked In North

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

Wide-angle photo showing many oaks across northern Wisconsin with partially defoliated, thin, and yellow-tinted crowns caused by defoliation from the oak leafroller and oak leaftier.

Many oaks across northern Wisconsin displayed partially defoliated, thin, and yellow-tinted crowns caused by defoliation from the oak leafroller and oak leaftier. / Photo Credit: Paul Cigan, Wisconsin DNR

A three-year-long outbreak of oak leafroller moth and oak leaftier moth—two native, early-season oak defoliators—continued this spring in northern Wisconsin, leaving behind tens of thousands of acres of oak-dominated forest with scattered, widespread defoliation.

Partially defoliated, thin and yellow-tinted crowns were visible across portions of Barron, Rusk, Sawyer and Washburn counties, as well as areas in Florence, Forest, northern Marinette and Vilas counties.

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