Oak Wilt Control: A Thousand-Foot View

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A view of two pockets of oak wilt treatment areas using the girdle-herbicide treatment, one from the previous year (bottom, yellow circle) and one from the current year (top, blue circle), captured from an airplane. / Photo Credit: Wisconsin DNR

By Alex Hornung, Forest Health Specialist, Plover
Alexandra.Hornung@wisconsin.gov

An aerial survey was conducted in late August over parts of Lincoln and Taylor counties, primarily looking for new oak wilt infection centers.

A rare glimpse of what oak wilt control can look like was captured from the vantage point of the airplane. The photo below shows a girdle-herbicide oak wilt control treatment from this year, with trees dying; and another from last year, with dead trees standing.

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Parts Of Northern Wisconsin Experience “Exceptional Drought” Conditions

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By Bill McNee, DNR Forest Health Specialist, Oshkosh
Bill.McNee@wisconsin.gov

map

A Wisconsin map showing drought conditions as of October 6, 2026. Map created by David Mocko, NASA/GSFC/SSAI. / Graphic Credit: Wisconsin DNR

Property owners and land managers in the northern half of Wisconsin are encouraged to monitor forest stands and ornamental trees for signs of decline and mortality due to the intensity of the current drought. In late September, parts of several counties reached the “Exceptional Drought” condition on the U.S. Drought Monitor (see maps). This is the most severe drought category used and it has only been seen in Wisconsin one other time since the U.S. Drought Monitor was created in 1999 (source: National Weather Service).

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Drought Impacts Young Aspen In North Central Wisconsin

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A portion of an aspen stand showing many leaves dropped due to drought, taken Sept. 2, 2026. / Photo Credit: Wisconsin DNR

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

Drought impacts can show up abruptly or have a slower impact, with symptoms becoming visible over the next one to two years.

North central and northwestern Wisconsin have faced significant drought conditions over several months this summer.

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Free Hemlock Woolly Adelgid Survey Training Opportunity

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Mitch Lannan of the Wisconsin Department of Agriculture, Trade and Consumer Protection, shows a hemlock branch infected by hemlock woolly adelgid. / Photo Credit: Wisconsin DATCP

By Wisconsin Department of Agriculture, Trade and Consumer Protection

Are you interested in learning how to help protect the health of Wisconsin’s hemlocks? A new interactive opportunity is being offered this fall by the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) to monitor for hemlock woolly adelgid (HWA).

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Autumn Is A Great Time To Treat Invasive Plants

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A nonnative honeysuckle plant with berries. / Photo Credit: Wisconsin DNR

By Wisconsin DNR

As temperatures begin to decline, the leaves of many plants and trees have begun to change color. Some trees in the northern part of the state have already begun dropping leaves.

The Wisconsin Department of Natural Resources (DNR) reminds the public that in addition to enjoying the changing hues in the woods, fall also presents a great opportunity to spot invasive plants.

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DNR Now Accepting Seedling Orders

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Rows of pine and tamarack seedlings in late March at the Wilson State Nursery. / Photo Credit: Wisconsin DNR

By Joe Vande Hey, DNR Reforestation Team Leader
Joseph.VandeHey@wisconsin.gov or 608-574-4904

As of Monday, the Wisconsin Department of Natural Resources (DNR) has begun accepting seedling orders from Wisconsin landowners who plan to plant them in spring 2027.

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Sapstreak Of Sugar Maple An Oldie But A Goodie

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DNR Forester Paul Etten stands at the base of a sugar maple tree that has small leaves and a thin crown. The tree was dissected and found to have extensive sapwood streaking. / Photo Credit: Wisconsin DNR

By Alex Hornung, DNR Forest Health Specialist, Plover
Alexandra.Hornung@wisconsin.gov

There are some tree diseases that really get a lot of attention and others that get lost in historical documents, only popping up now and again to ignite excitement within the local plant pathologist community.

Maple sapstreak is one of the latter. This year, a site in Shawano County was found to have several trees experiencing symptoms of the disease. The symptoms led to a positive identification of maple sapstreak.

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White Pine Weevil Also A Problem On Spruce

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Damage to terminal leader of an understory white pine in Portage County. / Photo Credit: Wisconsin DNR

By Alex Hornung, DNR Forest Health specialist, Plover
Alexandra.Hornung@wisconsin.gov

This is a great time of year to be looking for or observing damage from the white pine weevil.

The insect is native and causes terminal leader mortality in susceptible species. Despite the name, there are numerous species of trees that are attacked in addition to white pine, including Norway spruce, jack pine, white spruce and many more.

The damage from white pine weevil is more evident when the needles on the main leader are still attached and are brown in color, primarily in the month of July through the winter of the year that the damage occurred. It is more difficult to see previous years’ damage, because the needles fall off and the dead terminal leader will either snap off or be bare. When the leader is killed, the branches below will grow in place of that leader and will eventually correct by self-selecting a new leader.

Chip cocoons and a larva are found inside the killed terminal leader of a white pine tree. / Photo Credit: Wisconsin DNR

Every year, reports come out of the northern and central zone of damage, sometimes reaching 20% or more in pine/spruce plantings where trees are open-grown. An increased number of reports in plantings have been coming out of the central zone throughout this field season. This may be due to an increase in populations of the weevil this year, or a simple function of thriving plantings that have robust terminal leaders more susceptible to attack.

In forested stands, pesticides are not the primary method of control due to practicality and cost. Trees will very often self-correct, and natural predators will do better when there is an adequate population of the weevil to sustain them. Impacted trees may end up with a noticeable crook in the stem as they continue to grow. These trees can be targeted for removal during regularly scheduled thinnings as the trees mature.

Terminal leader damage is evident on planted white pine and spruce trees in Waushara County. / Photo Credit: Wisconsin DNR

For more information about white pine weevil in Wisconsin, please refer to this article from 2023, written by Linda Williams, Wisconsin Department of Natural Resources Forest Health specialist for the Northeast zone.

Fluffy White Stuff On Your Alder? It’s Woolly Alder Aphid

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Woolly alder aphids congregate on alder stems to spend the winter. / Photo Credit: Ryan Brown, Vilas County Forest

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

Woolly alder aphids spend their winters on alder stems and summers feeding on maple leaves. Large congregations of these aphids can be visible from a distance, and the bright white patches of aphids may catch your eye.

These plump bluish aphids, with white fluffy growths on their abdomens, are called woolly alder aphids when they’re found on alder – and maple blight aphids during the part of their life cycle when they’re feeding on maples.

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Scanlon To Speak At UMISC Conference

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A resistograph is used to measure the density of wood in a tree at Lizard Mound State Park in Washington County in June 2023. Wisconsin DNR Forest Health lab pathologist Kyoko Scanlon looks on. / Photo Credit: Bill McNee, Wisconsin DNR

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

Kyoko Scanlon, Forest Health Lab pathologist for the Wisconsin Department of Natural Resources, gave a presentation at the Upper Midwest Invasive Species Conference (UMISC), which was held Oct. 6-8 at the La Crosse (Wisconsin) Convention Center.

Scanlon updated attendees on a Heterobasidion root disease soil diversity study on Oct. 7.

The event, the largest invasive species conference in North America, was the group’s 10th biennial conference since 2008. Several speakers, programs, presentations, workshops, field trips and networking opportunities will make up the multiple-day event. More information can be found at the group’s website.

The conference addresses all types of invasive species, connecting the management, research and policy communities. The goal is to strengthen management of invasive species through prevention, control and containment. It also offers numerous opportunities to network with professionals, land managers, researchers, nonprofit organizations and others.

The group is a partnership between the Invasive Plants Association of Wisconsin, the Midwest Invasive Plant Network and the Minnesota Invasive Species Advisory Council.