Forest Health News

Basswood Trees Short On Leaves Due To Thrips

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

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

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

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

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

Over the night of June 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

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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Reminders About Spongy Moth Quarantine

By Meg Sanders, Wisconsin Department of Agriculture, Trade and Consumer Protection;
MeganT.Sanders@wisconsin.gov or 715-891-8158

The state Department of Agriculture, Trade and Consumer Protection (DATCP) works with the U.S. Department of Agriculture Animal and Plant Health Inspection Service (USDA-APHIS) to enforce a spongy moth quarantine in Wisconsin, with the goal of limiting the spread of the spongy moth to new, uninfested areas.

The quarantine now covers 53 of Wisconsin’s 72 counties. The quarantine regulates woody nursery stock, Christmas trees, firewood, logs and outdoor household items. Quarantine regulations apply to businesses and private citizens.

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Spongy Moth Status Update

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

A photo showing several trees with spongy moth defoliation in Marinette County in mid-June 2024.

Spongy moth defoliation in Marinette County in mid-June 2024. / Photo Credit: Darrek Sams, Wisconsin DNR

As of early July, we have seen a mix of live and dead caterpillars and tree defoliation that is typical of a late-stage spongy moth outbreak. Reports of defoliation have been received as far north as Florence County.

Recent aerial surveys in southern Wisconsin spotted defoliation in the same general areas as in 2023, but the defoliation has generally been less intense this year. Information for northern Wisconsin has yet to be made available. Refoliating oaks, growing a second set of pale-looking leaves, were seen in Walworth County in early July.

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‘Cicadapalooza’ Makes Noise In Lake Geneva

Photo showing dozens of recently emerged cicadas rest on a tree trunk at Big Foot Beach State Park in Lake Geneva on May 30, 2024.

Dozens of recently emerged cicadas rest on a tree trunk at Big Foot Beach State Park in Lake Geneva on May 30, 2024. / Photo Credit: Sarah Wolski, Wisconsin DNR

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

Brood XIII periodical cicadas apparently love Lake Geneva. The Wisconsin hotspot for Brood XIII has again been the resort city of Lake Geneva, located just a few miles from the Illinois border. It experienced Wisconsin’s first emergence of the insects’ latest 17-year cycle on May 17. Cicadas remained active – noisily so – through late June.

The city of Lake Geneva, joined by the University of Wisconsin-Madison Entomology department, celebrated the insects’ return with Cicadapalooza, a family-friendly, free pop-up event on June 8 that included guided walking tours, presentations by UW-Madison entomologists, cicada merchandise, food and more.

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Pruning Can Control White Pine Blister Rust

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

Eastern white pines (Pinus strobus) can be beautiful trees in urban and forested areas (they can tower above the rest of the forest’s trees), but they can also attract a deadly disease.

White pine blister rust (Cronartium ribicola), also known as WPBR, is a fungus that can attack branches and the main stem of white pine, causing cankers that continue to grow each year and creating dead spots that can girdle branches or the main stem. Damage from a girdling canker may take years to become severe enough to cause tree decline and mortality. That means you may be able to help your trees and prevent mortality.

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