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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Heterobasidion Root Disease Approaches

By Alex Feltmeyer, Forest Health Specialist, Plover, or 715-340-3810

A Heterobasidian root disease fruiting body at the base of a white pine sapling

A Heterobasidion root disease fruiting body is found at the base of a white pine sapling in the understory. Photo: Wisconsin DNR Forest Health

Heterobasidion Root Disease (formerly annosum root rot or Fomes root rot) is a serious disease of conifers that causes reduced height, shoot and diameter growth along with thin and yellowish/red foliage, ultimately causing mortality.

The disease becomes established in a new stand when spores of the fungus land on freshly cut stumps made by any forest management that creates cut stumps. After the disease becomes established, it spreads underground through root systems into adjacent trees. In this way, we often find pockets or groups of trees in various stages of decline.

Movement through the root systems contributes to significant spread throughout stands of conifers, impacting the regeneration of conifers within these pockets.

Mortality usually starts occurring three to eight years after a thinning operation. During this time, perennial fruiting bodies of the fungus begin to develop around the base of cut stumps or dead trees.

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Hungry Squirrels Find Trees Tasty

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

Maple branches with light colored areas where squirrels removed bark.

Squirrels remove the bark of maples, leaving bright bare spots. Photo: Wisconsin DNR

It’s the time of year when we start to see scattered maple trees stripped of their bark. Squirrels cause this damage — which can be limited to a few small areas the size of a tennis ball or can extend to cover many feet of branches or the main stem.

The squirrels are going after the cambium layer, just under the bark, that tastes slightly sweet from the sap. Smooth bark is easier for squirrels to chew, so young trees or branches with thin bark are likelier to be stripped than those with older, furrowed bark.

At this time of year, the pale wood of the branches that have had the bark stripped off is nearly white; later in the season, this wood will darken or even turn black with sooty mold. This type of feeding can remove enough bark to girdle the branches or the main stem, causing the tree to die from that point to the end of the branch.

Branches that are not completely girdled will continue to grow, and callus tissue will begin to grow over the wounds. If branches are nearly girdled, they may leaf out this spring and then suddenly wilt and die as hot weather hits because the tree can’t deliver enough water to keep those leaves alive. Continue reading “Hungry Squirrels Find Trees Tasty”

More Than 1,000 Wisconsin Municipalities Now Known To Have Emerald Ash Borer

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

In 2022, the number of municipal emerald ash borer (EAB) detections in Wisconsin crossed the 1,000 milestone. The 1,000th municipality (town, village or city) to have an EAB detection was the Town of Lincoln in Adams County on May 19. At the end of the year, EAB was known to be in 1,109 municipalities, up 23% from a year earlier.

Graph showing cumulative number of Wisconsin municipal emerald ash borer detections by year.

Cumulative number of Wisconsin municipal EAB detections by year. Graph: Bill McNee, Wisconsin DNR.

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First Anniversary Of Spongy Moth’s Name Change

Spongy moth caterpillar

Spongy moth caterpillar. Photo credit: Jon Yuschock,

March 2, 2023, marks one year since a new common name for Lymantria dispar, spongy moth, replaced the prior name of this insect, “gypsy moth.” This change was necessary because the word “gypsy” is an ethnic slur for the Romani people and the former common name equated people with insects. This is the first name change undertaken by ESA (Entomological Society of America)’s Better Common Names Project.

The current name—derived from the common name used in France and French-speaking Canada, “spongieuse“—refers to the moth’s sponge-like egg masses. Lymantria dispar is a damaging pest. This current name is a critical move in public awareness that focuses on an important feature of the moth’s biology while moving away from an outdated term. We encourage you to review any materials you may have on your website, ordinances and other material related to forest pests to ensure they are in accordance with this name change.

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Wisconsin DNR 2022 Forest Health Annual Report

By Becky Gray, Forest Health Team Leader,

The Wisconsin Department of Natural Resources’ Forest Health team recently completed the 2022 Forest Health Annual Report. The report summarizes impacts from pests, diseases and weather on the health of Wisconsin’s forests. Highlights from 2022 include:

  • Spongy moth’s rising numbers and evaluation of control techniques;
  • emerald ash borer continuing to spread and kill ash trees;
  • possible new biological control of buckthorn; and
  • drought and flooding impacts alongside insect infestations.

Read the report here.

2022 Forest Health Annual Report

Make Plans To Control Spongy Moth Before The Eggs Hatch

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

Spongy moth (formerly known as gypsy moth) egg masses typically begin to hatch in April as temperatures warm. Each mass that hatches may produce up to 1,000 leaf-eating caterpillars.

Now is a great time to inspect your trees for egg masses and treat or remove any masses within reach. Wisconsin weather has been favorable for this pest over the last three years and populations have grown.

Photo of three spongy moth egg masses on the underside of a pine branch in Walworth County.

Three spongy moth egg masses on the underside of a pine branch in Walworth County. Photo: Bill McNee, Wisconsin DNR.

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