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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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.

Garlic Mustard Aphid Advances

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

Photo of garlic mustard aphids on a leaf.

Dozens of garlic mustard aphids feed on the underside of a garlic mustard leaf in Michigan. The small, dark aphids, originally from Europe, have been found in Wisconsin and other states after first being discovered in Ohio in 2021. Photo: Rebecah Troutman, Holden Forests and Gardens, Kirtland, Ohio.

A new tool in the effort to fight invasive garlic mustard appears ready to make its move in Wisconsin.

The garlic mustard aphid, Lipaphis alliariae, has been moving westward after being discovered in Ohio in 2021. Since then, isolated populations have also been found in Wisconsin, Connecticut, Massachusetts, Michigan and Minnesota.

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USDA Biological Control Facility Seeks Ash Trees To Battle Emerald Ash Borer

Asks Landowners To Donate Infested Ash Trees

USDA staff cut a ‘bark window’ in green ash to uncover signs of emerald ash borer. Photo credit: USDA

The U.S. Department of Agriculture (USDA) is asking Wisconsin landowners for their help. Emerald ash borer (EAB) is an invasive insect from Asia that was first introduced into the United States in 2002. Since its discovery, EAB has caused the death and decline of tens of millions of ash trees. USDA uses ash trees to combat the pest to help preserve and protect the tree species.

Wisconsin landowners have donated live, infested ash trees to USDA’s EAB biological control program. The wood is used to grow EAB’s natural enemies and release them in Wisconsin and 31 other infested States as well as D.C. where they are attacking and killing EAB. USDA needs more ash trees to continue this work and is hoping more Wisconsin residents will consider donating their ash trees this year.

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Prepare — Spongy Moth Caterpillars To Return

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

Spongy moth caterpillars clustered below a sticky barrier.

Spongy moth caterpillars clustered below a sticky barrier. Photo: Mark Guthmiller, Wisconsin DNR

This June and July, spongy moth populations are predicted to reach damaging levels in parts of Wisconsin. Populations began to rise in 2020, and this is likely to be the third year of the pest outbreak in some regions of southern Wisconsin.

At present, damaging populations are expected to be most noticeable in southern counties, counties to the north of the city of Green Bay, and in far northern Wisconsin near Lake Superior. Additional areas are likely to have high populations that are more concentrated in size.

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Report Tree-Of-Heaven To Help Monitor For Spotted Lanternfly

By Anne Pearce, Invasive Plants Association of Wisconsin

Spotted lanternfly is on its way to Wisconsin

Tree-of-heaven showing leaves and fruits. Photo: Chuck Bargeron, University of Georgia,

Spotted lanternfly (Lycorma delicatula) is an invasive insect that threatens a variety of plant species, mostly woody plants. It has not yet been found in Wisconsin, but it is steadily moving toward us from the eastern United States. Both juvenile (nymphs) and adult spotted lanternfly feed by sucking sap from the stem, branches, twigs and leaves of host plants. This weakens the plant and can contribute to the plant’s death. Because spotted lanternfly impacts a wide variety of agricultural crops (like grapes and hops), nursery crops (like roses), and hardwood trees (like maple, walnut, willow, and poplar), it is a high priority pest in Wisconsin.

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First Recovery of Emerald Ash Borer Enemy Made

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

Map showing Spathius Galinae recovery in Manitowoc County

Sites where EAB biological controls have been recovered as of March 2023. The Spathius galinae recovery site is indicated by a red star. Blue dots show Tetrastichus planipennisi recovery sites. Municipal EAB detections are in green. Map: Wisconsin DNR

Two adult wasps, collected last December as pupae from an emerald ash borer (EAB) gallery at Kiel Marsh State Wildlife Area in Manitowoc County, have recently been identified as Spathius galinae.

This find marks the first time that S. galinae has been recovered in Wisconsin, confirming that the adult wasps released at this site over the last few years were able to attack EAB larvae and reproduce successfully. The “EAB wasps” were released as biological controls to help reduce EAB populations over the long term.

This wasp species has a longer ovipositor than the other EAB larval parasitoid currently released in Wisconsin (Tetrastichus planipennisi), allowing S. galinae to attack EAB larvae that are beneath thicker bark.

Spathius galinae was first released in Wisconsin in 2016, and approximately 1,000 of this species were released at Kiel Marsh in 2019 and 2020. Recovery surveys are conducted several years after initial releases, giving the wasps time to reproduce and spread. Continue reading “First Recovery of Emerald Ash Borer Enemy Made”

Aerial Spraying Set For Four State Sites

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

Spray aircraft used in spongy moth control

Spray aircraft used in spongy moth control. Photo: Bill McNee

At a suitable time between early May and early June, an airplane will spray parts of four DNR properties to reduce the population of spongy moth caterpillars (formerly known as gypsy moth). Treatment dates will depend on weather conditions and caterpillar development.

This year’s high populations threaten to strip trees of their leaves and possibly kill high-value trees at these properties.

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