Northern WI Forest Health

Tan Tamaracks? It Could Be Larch Casebearer

Posted on by akabelowsky
A photo showing severe defoliation of a tamarack tree by larch casebearer, with most needles mined out by the larvae.

Severe defoliation of a tamarack tree by larch casebearer shows most needles mined out by the larvae. / Photo Credit: Linda Williams, Wisconsin DNR

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

If you’ve noticed tamarack trees with tan or light-brown foliage, you’re probably seeing the work of the larch casebearer.

As foliage began to expand this spring, the caterpillars of this invasive moth became active and began to feed. The tiny caterpillars mine out the needles of tamarack and use them as “cases” to protect themselves, hence their name.

Continue reading “Tan Tamaracks? It Could Be Larch Casebearer” →

Yellow Needles On White Pine This Spring

Posted on by akabelowsky
A closeup photo showing current-year white pine needles emerging among yellow needles that show spots and banding.

Current-year white pine needles emerge among yellow needles that show spots and banding. / Photo Credit: Linda Williams, Wisconsin DNR

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

In North Central Wisconsin, some Eastern white pine had needles that turned a bright yellow color in early June, then quickly dropped from the trees by the end of June.

These trees will now look rather thin throughout the summer, until new foliage can fully expand and start to fill in the crown. Most damage has been noted in Oneida and Vilas counties, with scattered instances in other counties. Continue reading “Yellow Needles On White Pine This Spring” →

Woolly Elm Aphid Causes Elm Leaves To Curl

Posted on by akabelowsky
Closeup photo of a group of elm leaves that show varying levels of wrinkling and curling, due to feeding by wooly elm aphids on the underside of the leaves.

A group of elm leaves shows varying levels of wrinkling and curling, due to feeding by wooly elm aphids on the underside of the leaves. / Photo Credit: Linda Williams, Wisconsin DNR

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

Woolly elm aphids (Eriosoma americanum) are a minor pest of American elm. The aphids’ feeding causes leaves to curl at the edges and develop a characteristic wrinkled appearance.

Uncurling the leaves exposes many pale gray aphids on the underside of the leaves, which are protected by the rolled leaf.

Continue reading “Woolly Elm Aphid Causes Elm Leaves To Curl” →

Spongy Moth Population In Decline

Posted on by akabelowsky
A photo of a tree trunk showing spongy moth caterpillars killed by nucleopolyhedrosis virus (NPV) hang in an inverted “V” orientation; caterpillars killed by the fungus Entomophaga maimaiga hang vertically.

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

By Michael Hillstrom, Wisconsin DNR Forest Health Specialist
Michael.Hillstrom@wisconsin.gov; 608-513-7690

Spongy moth caterpillars began hatching at the end of April in 2025 and are now actively feeding on leaves. In most Wisconsin locations, though, the population will not be as high as it has been in the last few years.

Wisconsin has had the largest outbreak in state history over the past few years. Fortunately, the outbreak collapsed in many areas of the state in 2024. The wet spring weather in April and May of 2024 allowed a fungus and a virus that infects spongy moth caterpillars to cause heavy mortality. Although some hot spots still exist in south central and northeast Wisconsin, we expect those populations to decline in 2025.

Continue reading “Spongy Moth Population In Decline” →

Watch For Oak Wilt Symptoms

Posted on by akabelowsky
A wide-angle photo showing an oak tree in the center that died rapidly from oak wilt during the summer of 2024.

An oak tree (center) that died rapidly from oak wilt during the summer of 2024. / Photo Credit: Wisconsin DNR

By Michael Hillstrom, Wisconsin DNR Forest Health Specialist
Michael.Hillstrom@wisconsin.gov or 608-513-7690

Oak wilt symptoms typically begin to appear in southern Wisconsin in late June and in northern Wisconsin during July.

Watch for browning leaves, starting at the top of the canopy and progressing downward. Most leaves will fall from infected trees as they die, typically within two to four weeks.

Continue reading “Watch For Oak Wilt Symptoms” →

More Spruce Budworm Defoliation Expected

Posted on by akabelowsky
A close-up photo showing young spruce budworm larvae beginning to feed as buds break, causing the new growth to crook where feeding damage occurs. Webbing is also common.

Young spruce budworm larvae begin feeding as buds break, causing the new growth to crook where feeding damage occurs. Webbing is also common. / Photo Credit: Linda Williams, Wisconsin DNR

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

From early indications, the spruce budworm outbreak in some areas of northern Wisconsin is preparing to continue for yet another year.

During the third week of May, expanding buds on balsam fir trees were already showing damage from the tiny larvae.

Continue reading “More Spruce Budworm Defoliation Expected” →

What’s That Under The Bark Of Red Pines?

Posted on by akabelowsky
A close-up photo showing pitch blobs near the base of a red pine, indicating attack by red turpentine beetle.

Pitch blobs near the base of a red pine indicate attack by red turpentine beetle. / Photo Credit: Linda Williams, Wisconsin DNR

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

Red turpentine beetle and pine root collar weevil are the most common insects found attacking near the base of red pine trees in Wisconsin, whether near ground level or just below ground level.

Here are some tips on identifying and controlling these pests.

Continue reading “What’s That Under The Bark Of Red Pines?” →

Forest Tent Caterpillar Outlook Stays Low

Posted on by akabelowsky
A close-up photo showing forest tent caterpillar larvae displaying gregarious behavior and feeding on a tree leaf.

Forest tent caterpillar larvae displaying gregarious behavior and feeding on a tree leaf. / Photo Credit: Paul Cigan, Wisconsin DNR

By Paul Cigan, Wisconsin DNR Forest Health Specialist
Paul.Cigan@wisconsin.gov or 715-416-4920

Forest tent caterpillar (FTC) populations do not appear to be making a significant return this growing season.

Spring egg mass surveys indicate that populations continue to remain low, continuing the longest documented interphase between outbreaks on state record, at 22 years and counting. The interphase provides some relief for the health of aspen stands recovering from several consecutive years of recent spongy moth defoliation.

Continue reading “Forest Tent Caterpillar Outlook Stays Low” →

Red Pine And Hemlock Needles Suddenly Looking Brown

Posted on by akabelowsky
A photo showing hemlock needles affected by winter desiccation that have started browning at the needle tips and moving inward, sometimes killing the entire needle.

Hemlock needles affected by winter desiccation will start browning at the needle tips and move inward, sometimes killing the entire needle. / Photo Credit: Linda Williams, Wisconsin DNR

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

During the winter months, warm or sunny weather can wreak havoc on evergreen trees.

Conifers such as hemlock, pines and fir can lose moisture from their needles during the winter. If too much moisture is lost, those needles can quickly turn yellow or brown once the weather warms up in the spring.

Extensive browning of needles on hemlock — sometimes more than 50 percent of the needles – was observed in scattered areas of Oneida and Bayfield counties by the second week of April. The brown needles eventually dropped from the trees, leaving the remaining foliage looking very thin. Buds on the trees appeared viable, and the trees should break bud as normal.

Continue reading “Red Pine And Hemlock Needles Suddenly Looking Brown” →

SilviCast Digs Into The Buckthorn Battle

Posted on by akabelowsky
The logo for the Silvicast, a podcast hosted by Wisconsin DNR silviculturists Greg Edge and Brad Hutnik and produced by the University of Wisconsin-Stevens Point's Wisconsin Forestry Center.

The logo for the Silvicast, a podcast hosted by Wisconsin DNR silviculturists Greg Edge and Brad Hutnik and produced by the University of Wisconsin-Stevens Point’s Wisconsin Forestry Center. / Graphic Credit: UW-Stevens Point

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

They talked about pulling it, smothering it, using herbicide on it, making turkey calls and making curtain rods from it.

They even wondered if they should just “kill it with fire.”

But it seems Midwestern foresters’ never-ending battle against buckthorn requires a brainier approach.

Continue reading “SilviCast Digs Into The Buckthorn Battle” →