Pests

Check Conifers For Invasive Adelgids

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Photo showing white, cottony hemlock woolly adelgid egg sacs on a hemlock branch.

White, cottony hemlock woolly adelgid egg sacs on a hemlock branch. / Photo Credit: Bill McNee, Wisconsin DNR

By Michael Hillstrom, DNR Forest Health Specialist, Fitchburg; Michael.Hillstrom@wisconsin.gov

Hemlock woolly adelgid (HWA) and balsam woolly adelgid (BWA) are invasive, aphid-like insects that cause tree mortality in North America. Neither has been found in Wisconsin so far, but they are likely to arrive at some point, as they have been confirmed in Michigan.

HWA (Adelges tsugae) is an invasive, sucking insect pest of hemlock trees. The white, cottony egg sacs of HWA can be seen on the undersides of hemlock branches at the base of needles year-round. HWA saliva enters the tree while feeding. The saliva is toxic and causes needle drop and twig dieback, progressing to tree mortality in 4-10 years.

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New Invasive Pest Discovered In Wisconsin

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

A closeup of an elm zigzag sawfly caterpillar consuming a leaf. The invasive insect, new to Wisconsin, was found on an elm tree near the Wisconsin Department of Natural Resources office in Oshkosh on July 16, 2024.

A closeup of an elm zigzag sawfly caterpillar consuming a leaf. The invasive insect, new to Wisconsin, was found on an elm tree near the Wisconsin Department of Natural Resources office in Oshkosh on July 16, 2024. / Photo Credit: Bill McNee, Wisconsin DNR

The invasive insect elm zigzag sawfly (Aproceros leucopada) has been detected in Wisconsin for the first time.

Following the initial Wisconsin discovery in Portage County on July 4. Through Aug. 12, the pest has since been detected in 17 Wisconsin counties. Continue reading “New Invasive Pest Discovered In Wisconsin” →

Larch Casebearer Damage Spotted In North

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

Photo showing a tamarack tree branch with severe needle mining from larch casebearer. / Photo Credit: Paul Cigan, Wisconsin DNR

A tamarack branch shows severe needle mining from larch casebearer. / Photo Credit: Paul Cigan, Wisconsin DNR

Larch casebearer has caused localized heavy defoliation in some tamarack swamps in central Burnett County this spring, causing tamarack to stand out with a stark appearance of bright-brown foliage by mid-June.

Larvae of this exotic moth damage tamarack needles by “mining” the inner needle tissue. Heavily damaged tamarack progress in color from pale green to yellow and eventually turn a bright, reddish brown as needles dry out and die.

 

 

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Spruce Budworm Defoliation Continues

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

Closeup photo showing that webbing created by the spruce budworm caterpillar holds needles and frass and protects the caterpillar. A pupa hangs from the branch.

Webbing created by the spruce budworm caterpillar holds needles and frass and protects the caterpillar. A pupa hangs from the branch. / Photo Credit: Linda Williams, Wisconsin DNR

Although symptoms weren’t as prevalent as in 2023, this year marked yet another year of defoliation from spruce budworm.

Another severe year of defoliation causes additional stress on the trees. Even though there has been a lot of rainfall this spring, it’s still stressful for the trees to face repeated years of defoliation by spruce budworm before they begin to decline and die.

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Dropping Leaves May Indicate Oak Wilt

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

Photo showing that oak leaves that drop from a tree infected with oak wilt may be all brown or all green, or often they will have green near the base of the leaf and the outer portions will be brown or watersoaked green.

Oak leaves that drop from a tree infected with oak wilt may be all brown or all green, or often they will have green near the base of the leaf and the outer portions will be brown or watersoaked green. / Photo Credit: Linda Williams, Wisconsin DNR.

The middle of summer is the time to start watching oak trees for symptoms of oak wilt. Although symptoms show up suddenly and leaves drop quickly, symptoms can emerge anytime between now and when leaves turn color in the fall.

Trees that were wounded in the spring and became infected with the fungus that causes oak wilt will usually die that same year. In established oak wilt pockets, the fungus moves underground through grafted root systems and trees will wilt as the fungus moves into the tree.

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Tubakia Leaf Disease Affects Red Oak

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

A tree showing that lower branches are thin and have lost leaves due to Tubakia leaf spot, while leaves on its upper branches look good.

A tree showing that lower branches are thin and have lost leaves due to Tubakia leaf spot, while leaves on its upper branches look good. / Photo Credit: Linda Williams, Wisconsin DNR.

Tubakia leaf spot is a leaf disease caused by a fungus (Tubakia dryina) that typically affects the lower canopy of red oaks.

Because of all the rain that came during the spring and early summer of 2024, the fungus has started to impact some trees. Problems didn’t occur last year because the weather was too dry.

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Emerald Ash Borer Confirmed In All 72 Counties

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

Closeup photo of an adult emerald ash borer. The pest has been detected in Burnett County, making it the 72nd and final county in Wisconsin that have confirmed presence of the invasive insect.

The emerald ash borer has been detected in Burnett County, making it the 72nd and final county in Wisconsin that have confirmed presence of the invasive insect. / Photo Credit: Paul Cigan, Wisconsin DNR

Sixteen years after the Wisconsin Department of Natural Resources (DNR) first detected emerald ash borer (EAB) in Wisconsin, the invasive beetle has been found in the last county without a previous detection.

Burnett County, in northwest Wisconsin, is the 72nd and final county to have a detection of the tree-killing pest.

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Basswood Trees Short On Leaves Due To Thrips

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

Photo showing Basswood leaves that have been damaged due to the feeding of introduced basswood thrips.

Basswood leaves show damage due to the feeding of introduced basswood thrips. / Photo Credit: Linda Williams, Wisconsin DNR

For the third consecutive year, damage from introduced basswood thrips (Thrips calcaratus) is significant in some areas of northeast Wisconsin, especially Forest County.

Introduced basswood thrips are tiny, invasive insects that feed inside tree buds in early spring. The feeding causes leaves to deform when they expand, looking like they suffered frost or wind damage.

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Oak Moth Outbreaks May Have Peaked In North

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

Wide-angle photo showing many oaks across northern Wisconsin with partially defoliated, thin, and yellow-tinted crowns caused by defoliation from the oak leafroller and oak leaftier.

Many oaks across northern Wisconsin displayed partially defoliated, thin, and yellow-tinted crowns caused by defoliation from the oak leafroller and oak leaftier. / Photo Credit: Paul Cigan, Wisconsin DNR

A three-year-long outbreak of oak leafroller moth and oak leaftier moth—two native, early-season oak defoliators—continued this spring in northern Wisconsin, leaving behind tens of thousands of acres of oak-dominated forest with scattered, widespread defoliation.

Partially defoliated, thin and yellow-tinted crowns were visible across portions of Barron, Rusk, Sawyer and Washburn counties, as well as areas in Florence, Forest, northern Marinette and Vilas counties.

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Pruning Can Control White Pine Blister Rust

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

Eastern white pines (Pinus strobus) can be beautiful trees in urban and forested areas (they can tower above the rest of the forest’s trees), but they can also attract a deadly disease.

White pine blister rust (Cronartium ribicola), also known as WPBR, is a fungus that can attack branches and the main stem of white pine, causing cankers that continue to grow each year and creating dead spots that can girdle branches or the main stem. Damage from a girdling canker may take years to become severe enough to cause tree decline and mortality. That means you may be able to help your trees and prevent mortality.

Continue reading “Pruning Can Control White Pine Blister Rust” →