Care for your woods

Acorn Pip Galls, Woolly Catkin Galls All The Same

By Linda Williams, DNR Forest Health Specialist, Woodruff; or 920-360-0665

Photo of acorns showing small pip galls.

Pip galls are small, tongue-like protrusions emerging from under the caps of acorns. / Photo Credit: Linda Williams, Wisconsin DNR.

Gall wasp life cycles can be complex. Did you know that acorn pip galls, which I’ve written about several times, have another part of their life cycle that is entirely different? This stage is called the woolly catkin gall.

Both woolly catkin galls and acorn pip galls are caused by Callirhytis quercusoperator, a species of cynipid gall wasp. This gall wasp takes two years to complete development by going through the two parts of its life cycle. Both parts of the life cycle are completed on northern red oak in our area.

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High Beech Scale Moving Beyond Door County

By Bill McNee, DNR Forest Health Specialist, Oshkosh; or 920-360-0942;

and Linda Williams, DNR Forest Health Specialist, Woodruff; or 920-360-0665

Photos of white 'wool' coating on trees with beech scale.

Examples of white “wool” coating on trees heavily infested with beech scale at Kohler-Andrae State Park (left) and in the Town of Beecher in Marinette County (right). / Photo Credit: Bill McNee (left) and Linda Williams (right), Wisconsin DNR.

Fourteen years after first detecting beech scale (Cryptococcus fagisuga, a non-native insect) in Door County, sites with high populations of beech scale have been found in additional counties. Beech scale is believed to have spread through the range of American beech in Wisconsin’s eastern counties, but until now has only been seen at low levels outside of Door County.

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White Pine Weevil Damage And Management Options

By Linda Williams, DNR Forest Health Specialist, Woodruff or 920-360-0665

Photo of a white pine tree showing weevil damage.

A dead terminal leader, resulting from an attack by white pine weevil. Photo: Linda Williams, Wisconsin DNR.

White pine weevil (Pissodes strobi) is a native insect that can kill the terminal leader of white pine, jack pine and spruce. Wisconsinites often refer to this insect as Tip Weevil.

The insects prefer to attack stout terminal leaders. When the terminal leader dies, lateral branches grow upward and compete to take over apical dominance. This can leave a noticeable crook for decades. If two or more lateral branches take over, forking can occur. New terminal leaders may be attacked in subsequent years, causing more crook or forking.

Spruce and jack pine tend to recover better from weevil damage than white pine because the lateral branch that takes over apical dominance often creates a less prominent crook.

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Is it Invasive Giant Hogweed?

Erika Segerson-Mueller, DNR Forest Health invasive plants program specialist, Oshkosh or 715-492-0391

Photo of umbel of a giant hogweed plant.

Umbel of a giant hogweed plant. This invasive plant can grow stems 2-4 inches in diameter and can grow as tall as 15 feet. Photo: USDA APHIS PPQ, Oxford, North Carolina;

This time of year, calls start rolling in about potential sightings of the invasive plant giant hogweed (Heracleum mantegazzianum). Although occurrences of the plant remain rare in Wisconsin, from late May through early July giant hogweed is often confused with a native plant, cow parsnip (Heracleum maximum).

Both are large plants with similar habitat preferences. They prefer shady areas and are often found along stream banks, roadsides and ditches. Giant hogweed is a prohibited species under Wisconsin’s Invasive Species Rule NR40. Its fast growth rate crowds out native vegetation and erodes soil, and skin contact can potentially cause irritation.

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Eastern Tent Caterpillar Webs Common

Linda Williams, DNR Forest Health Specialist, Woodruff or 920-360-0665

Photo of web of eastern tent caterpillars.

Eastern tent caterpillars and their webs start out small but grow quickly. Photo: Linda Williams, Wisconsin DNR.

Have you seen trees along roadsides with white webs in them? Eastern tent caterpillars (ETC) are hatching and beginning to feed on host trees, including cherry, apple and crabapple.

Landowners and homeowners may notice the white silken tents forming in branch forks. Although they form unsightly nests, ETC is a native insect, so management is not typically necessary. Even completely defoliated trees will produce new leaves within a few weeks.

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Diseases Take Aim At Spongy Moth

Photo of tree showing caterpillars killed by virus and fungus

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

By Bill McNee, DNR Forest Health Specialist, Oshkosh or 920-360-0942

With this spring’s dry weather in Wisconsin came predictions of the largest spongy moth population in years.

When spongy moth populations are high, we often see heavy mortality of the larger caterpillars due to two pathogens. Heavy caterpillar mortality will reduce the severity of the following year’s outbreak and often causes a population crash during the current year. If a heavy die-off of caterpillars is observed, please let your local DNR Forest Health Specialist know about it.

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Spongy Moth Focus Of Video, Webcast

Art Kabelowsky, DNR Forest Health outreach and communications specialist or 608-335-0167

Add “YouTube Influencer” to the long list of career accomplishments of Andrea Diss-Torrance, Ph.D.

With the spongy moth caterpillar population on the rise in many areas of Wisconsin this season, the Wisconsin Department of Natural Resources stepped into action last month.

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ATCP 21 Rule Changes Coming

Art Kabelowsky, DNR Forest Health outreach and communications specialist or 608-335-0167

Photo of an adult emerald ash borer.

The statewide quarantine for emerald ash borer will end July 1, as one of several permanent rule changes proposed by the Wisconsin Department of Agriculture, Trade and Consumer Protection.

Changes are coming to some of Wisconsin’s rules for plant inspection and plant control, following legislative approval of a proposal from the Department of Agriculture, Trade and Consumer Protection (DATCP).

The rule changes for ATCP 21 (Clearinghouse Rule CR 22-022), in the works since 2020, will go into effect on July 1.

One of the permanent rule changes involves the end of the state quarantine for emerald ash borer. Other quarantines to be rescinded are those for pine shoot beetle and thousand cankers disease of walnut trees.

The changes were recommended by DATCP for one or more of the following reasons: a lack of serious pest impacts, the quarantine outliving its ability to contain the pest, and/or federal deregulation.

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Multiple Oak Defoliators Active Now

Photo of oak leafroller caterpillar on a leaf.

Oak leafroller caterpillars web leaves together as they feed. Photo: Wisconsin DNR.

Linda Williams, DNR Forest Health Specialist, Woodruff or 920-360-0665

Watch for defoliators in your oak trees this summer. You may have already heard news reports about spongy moth caterpillar populations being high this year, but there are some native caterpillars to watch for this year as well.

In 2022, oak leafroller caterpillars caused significant defoliation to oaks in areas of northeastern and northwestern Wisconsin, as well as in Blue Mound State Park. Many other areas experienced lesser amounts of defoliation from oak leafroller.

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Emerald Ash Borer Found In Polk County

Photo of Emerald Ash Borer larvae in a tree

Emerald ash borer has been discovered in Polk County for the first time. The invasive pest now has been found in 68 of Wisconsin’s 72 counties. Photo: Wisconsin DNR.

Paul Cigan, DNR plant pest and disease specialist
715-416-4920 or

Emerald ash borer (EAB) was detected for the first time in Polk County this spring, making it the 68th of Wisconsin’s 72 counties in which the invasive pest was found since it was first discovered in the state in 2008.

Several green ash trees with woodpecker flecking were observed in the roadside right-of-way along 100th Avenue in the Town of Osceola during field work.

Two larvae were collected from an infested tree and officially confirmed as EAB by a USDA-APHIS identifier on May 8, 2023.

No regulatory changes have resulted from this detection because EAB was federally deregulated on Jan. 14, 2021, and Wisconsin instituted a statewide quarantine in 2018.

EAB will continue to spread in northern Wisconsin, significantly impacting the ash resource. This is a good time to review the DNR’s updated emerald ash borer webpage for information and resource links on EAB, along with the DNR’s EAB Silviculture Guidelines to become familiar with or to refresh on ash stand management options.

DATCP, DNR, UW Extension and tribal partners continue to track EAB’s spread, sharing detection information through online maps available to Wisconsin’s citizens, private businesses and governmental entities. The goal is to aid in EAB readiness planning, pest management and biological control activities.

With more than 20 new city/town/village detections already reported statewide in 2023, map updates continue to occur on a biweekly basis. To see where EAB has been found in Wisconsin or to report new municipal detections, please visit the Wisconsin EAB online detections map or PDF map.