Pest

After A Quiet Year, Conduct Spongy Moth Egg Mass Surveys This Fall

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The only mature spongy moth caterpillar detected at Harrington Beach State Park in Ozaukee County in July 2026 crawls up a tree’s mainstream. / Photo Credit: Wisconsin DNR

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

Wisconsin’s recent period of high spongy moth (Lymantria dispar) populations came to an end in 2025 and the population remained very low in 2026.

Only a handful of caterpillar reports were received, most often coming from southern Jefferson County and eastern Dane County. Most notably, numerous bur oaks were reported to be infested with several hundred caterpillars per tree in and around Cambridge, Fort Atkinson and Lake Mills; light feeding damage was visible.

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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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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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Needle Rust On Spruce, Fir And Hemlock

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closeu[p of balsam fir needles with needle rust

Balsam fir needles infected with needle rust turn bright yellow. / Photo Credit: Wisconsin DNR

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

Although this summer has been dry in north-central Wisconsin, there was enough moisture this spring to promote some needle rusts. Needle rusts are fungi that infect needles of various conifers. Most rusts require two hosts to complete their life cycle.

A look at common types of needle rust:

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Pitch Borer Mass On White Pine

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A pitch mass on a tree's main stem.

A pitch “glob”, with oozing pitch running down the trunk of a young white pine infected with pitch mass borer. / Photo Credit: Wisconsin DNR

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

Have you seen big globs of gooey pitch on the main stems of eastern white pine trees?  Or maybe you’ve seen them on spruce?

For those with an adventurous side, grab a stick and scrape off some of that gooey glob. You might be rewarded with the sight of large larvae feeding beneath all of that goo. This is the larvae of our native pitch mass borer. Adults are clearwing moths that look a bit like wasps.

Peeling reveals a pitch borer "goo" mass on a damaged tree.

Using a stick to pry away some of the gooey pitch on a tree exposes a pitch mass borer larva underneath. / Photo Credit: Wisconsin DNR

Adults lay eggs on the bark. When eggs hatch, the tiny larvae chew into the bark and begin feeding on the inner bark. They feed enough to irritate the tree, causing more sap and pitch to be produced, which the larvae feed on.

Pitch mass borer can take two to three years to complete development, remaining in that same location throughout their life and continuously irritating the inner bark to promote continued pitch production. Pupation occurs under the glob of pitch and adults then chew their way out. Old pitch globs will harden and darken over time, remaining on the tree for a year or more before finally weathering off.

Hosts include pines (eastern white, jack, scotch and Austrian) and spruces (blue and Norway).

Management on forest trees is not necessary. Severely damaged and deformed trees can be removed during the first thinning. Management on yard trees includes maintaining healthy trees (which are less attractive to the adults), watering during droughts, avoiding pruning during mid-summer (which can attract adults to lay eggs near the fresh wounds), destroying any larvae under the globs of pitch and removing and disposing of severely infested trees.

A pitch mass borer larva on a tree.

Scraping more pitch off a tree’s main stem shows a pitch mass borer larva on the end of the stick. / Photo Credit: Wisconsin DNR

A photo showing the whitish color of some pitch mass borer larvae.

Pitch mass borer larvae can be shades of white to pink, depending on the host. / Photo Credit: Wisconsin DNR

Tips For Identifying Asian Longhorned Beetle And Lookalikes

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Closeup of female Asian longhorned beetle.

A female Asian longhorned beetle has a shiny appearance, bright spots and black-and-white striped antennae. / Photo Credit: Bugwood.org

By Michael Hillstrom, DNR Invasive Forest Pest Coordinator
Michael.Hillstrom@wisconsin.gov

More than 300 species of longhorn beetles inhabit the Midwest. The invasive Asian longhorned beetle (ALB) is not yet one of them, with no Wisconsin populations reported.

But ALB’s potential for damage is great enough that state agencies are asking members of the public to be on the lookout for the insect — and to avoid being confused by a relative lookalike.

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Aspen Leaf Beetle Defoliation Found In North

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Closeup of beetles, and a cluster of eggs, on an aspen leaf.

Young larvae of aspen leaf beetle feed on the undersides of aspen leaves. The arrow points to the cluster of eggs that produced the larvae. / Photo Credit: Wisconsin DNR

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

Aspen leaf beetles have recently been spotted defoliating young quaking aspen trees in Vilas and Oneida counties.

Both adults and larvae will feed on aspen leaves. The defoliation level detected was light to moderate.

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Pine False Webworm Uncommon In Wisconsin

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Messy webbing filled with frass (droppings) and pieces of needles are signs of pine false webworm feeding on this young white pine. The arrow points to a pine false webworm larvae. / Photo Credit: Wisconsin DNR

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

Pine false webworm (Acantholyda erythrocephala) is not a very common insect in Wisconsin, though it is present. They prefer to feed on white pine in Wisconsin, though reference materials say they will also feed on red pine, jack pine and Scotch pine.

Damage was reported as “minor” in the central part of the state from 1953 to 1961. Later, in 1995, 1997, 2002, 2004 and 2006, it was once again observed as a minor pest feeding on red or white pine in the central part of the state, particularly Portage, Waupaca and Waushara counties. In 2024 and again this year, a few scattered young white pine were observed being significantly defoliated in Oneida and Vilas counties.

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Japanese Beetle Populations Still Building In The North

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Beetles feeding on a basswood leaf.

Japanese beetles defoliating a basswood leaf. / Photo Credit: Wisconsin DNR

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

The Japanese beetle (Popillia japonica) is an invasive insect that feeds on many plant species. The adult beetles “skeletonize” leaves by eating the material between the veins.

Adult Japanese beetles feed on the flowers and leaves of more than 300 plant species, including trees, shrubs and herbaceous plants. Forest trees can be defoliated, with open-grown or edge trees suffering the highest defoliation rates.

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