Southern WI Forest Health

Cottony Ash Psyllid Found In Additional Areas

Posted on by akabelowsky
Closeup photo showing how cottony ash psyllid nymphs feed on the lower sides of leaves and grow white wool over themselves for protection.

Cottony ash psyllid nymphs feed on the lower sides of leaves and grow white wool over themselves for protection. / Photo Credit: Wisconsin DNR

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

Cottony ash psyllid (Psyllopsis discrepans) was observed in 2023 in several areas in northern Wisconsin. Additional sites were then identified in 2024 and this year.

Some provinces in Canada have observed that psyllid numbers can explode during dry periods, so that may be why we started to see some issues in Wisconsin in 2023.

Continue reading “Cottony Ash Psyllid Found In Additional Areas” →

Hail Damage Can Cause Dieback, Whole-Tree Mortality

Posted on by akabelowsky
Photo of a young aspen showing signs of severe impact from hail. Arrows indicate each point of impact.

A young aspen shows signs of severe impact from hail. Arrows indicate each point of impact. / Photo Credit: Wisconsin DNR

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

Several high-impact storms across the state this summer have pummeled trees with hail. The photos accompanying this article show the kind of damage hail can bring to forests.

The initial damage following a significant hailstorm can immediately appear severe. But give it a month or two, and the damage can look even more pronounced.

Pines in particular will start to turn varying levels of brown, depending on the amount of damage they sustained. Damage to the branches and twigs is not limited to just the spot where the hail hit. As the summer goes on, damaged areas of bark that were cracked by the hail impact will often split open further and allow more drying and additional separation of the bark from the wood, which kills that area of the branch.

Continue reading “Hail Damage Can Cause Dieback, Whole-Tree Mortality” →

Bur Oak Blight Confirmed In Calumet County

Posted on by akabelowsky
Photo of a wedge-shaped area of dead tissue at the tip of a bur oak leaf from a tree infected with bur oak blight.

A wedge-shaped area of dead tissue at the tip of a bur oak leaf from a tree infected with bur oak blight. / Photo Credit: Wisconsin DNR

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

Recent laboratory examination has confirmed the presence of bur oak blight in Calumet County. The disease affects only bur oaks and is caused by the fungus, Tubakia iowensis.

Calumet County is the 35th Wisconsin county to have a confirmed detection of bur oak blight. The disease has not been microscopically confirmed in all counties where bur oak grows and is likely present in additional counties. Bur oak blight was first reported in Midwestern states in the 1990s.

Continue reading “Bur Oak Blight Confirmed In Calumet County” →

HRD Conks Found In Different Shapes And Sizes

Posted on by akabelowsky
Photo from above showing Heterobasidion root disease growing from an infected tree stump.

Heterobasidion root disease grows from an infected tree stump. / Photo Credit: Wisconsin DNR

By Kyoko Scanlon, DNR Forest Pathologist, Fitchburg
Kyoko.Scanlon@wisconsin.gov

Fall is a great time to look for mushrooms, including conks from trees infested with Heterobasidion root disease (HRD).

Considered one of the most destructive diseases of conifers in the northern hemisphere, the fungus causing HRD is very difficult to eradicate once established. Infestation of a conifer stand may significantly impact stand management, making early detection of the disease extremely important.

Continue reading “HRD Conks Found In Different Shapes And Sizes” →

Fall Webworm Spins Its Way To Attention

Posted on by akabelowsky
Photo of fall webworms form a tent on a tree at Kohler-Andrae State Park in September 2025.

Fall webworms form a tent on a tree at Kohler-Andrae State Park in September 2025. / Photo Credit: Wisconsin DNR

By Bill McNee, DNR Forest Health specialist, Oshkosh
Bill.McNee@wisconsin.gov, 920-360-0942

The native insect known as fall webworm (Hyphantria cunea) has been generating calls and emails from curious property owners over the past few weeks.

The caterpillars don’t draw much attention on their own; instead, what catches the eye at this time of year are the large webs (or “tents”) that they create on the tips of tree branches.

Continue reading “Fall Webworm Spins Its Way To Attention” →

Invasive Japanese Stiltgrass Detected In Three More Counties

Posted on by akabelowsky
Wide-angle photo of a mat of Japanese stiltgrass in Rock County, Wisconsin, in July 2025

A mat of Japanese stiltgrass in Rock County, Wisconsin, in July 2025. / Photo Credit: John Zaborsky, University of Wisconsin-Madison Renz Weed Science Lab

By Wisconsin DNR

Thanks to the help of eagle-eyed observers across southern Wisconsin, the harmful invasive plant Japanese stiltgrass (Microstegium vimineum) has now been detected in three additional counties. That brings the total number of Wisconsin counties to five.

The most recent detections of the non-native, annual grass came in Dane, Grant and Walworth counties. The Dane County find was in Middleton, northwest of Madison; in Grant County, it was found southeast of Wyalusing State Park; in Walworth County, it was found north of Geneva Lake.

Continue reading “Invasive Japanese Stiltgrass Detected In Three More Counties” →

Imported Willow Leaf Beetle Spotted

Posted on by akabelowsky
Closeup photo of an imported willow leaf beetle adult and larva.

An imported willow leaf beetle adult and larvae. / Photo Credit: Wisconsin DNR

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

Imported willow leaf beetle (Plagiodera versicolor) is a small, shiny, blue-black beetle as an adult, and the larvae are small, solid black and spikey. Both feed on the foliage of willow and poplar species. Two generations per year are possible.

The invasive pest was first detected in the United States in 1915, likely coming from eastern Europe.

Continue reading “Imported Willow Leaf Beetle Spotted” →

Introduced Pine Sawfly Found On White Pine

Posted on by akabelowsky

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

Photo of an introduced pine sawfly larva.

Introduced pine sawfly larva. / Photo Credit: Wisconsin DNR

The introduced pine sawfly was first found in the United States in 1914 and was first detected in Wisconsin in 1944.

Introduced pine sawfly larvae prefer feeding on white pine needles, although literature says they can also feed on jack pine, red pine and scotch pine. Larvae often feed singly, rather than in groups (like redheaded pine sawfly or European pine sawfly do). Larval sawflies can look like caterpillars, but these larvae develop into adult sawflies, which look like a fly or a chunky wasp.

Continue reading “Introduced Pine Sawfly Found On White Pine” →

White Pine Weevil Damage Is Easy To Spot

Posted on by akabelowsky
A photo showing that white pine weevil has attacked and killed the terminal leader on a young white pine.

White pine weevil attacked and killed the terminal leader on a young white pine. / Photo Credit: Wisconsin DNR

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

 Symptoms of white pine weevil attack are easily detected at this time of year, as damaged leaders turn dark brown and branch tips can curl or droop.

White pine weevil (Pissodes strobi) is a native insect that can attack and kill the terminal leader of white pine, jack pine and spruce. Another common name for this insect is “tip weevil.”

These insects prefer to attack stout terminal leaders.

Continue reading “White Pine Weevil Damage Is Easy To Spot” →

Oak Leaf Issues That Are Not Oak Wilt

Posted on by akabelowsky
Closeup photo showing oak wilt leaf symptoms on a red oak leaf. Leaves often show browning on the outer portions of the leaf while the base of the leaf will still have some normal green color.

Oak wilt leaf symptoms on a red oak leaf often show browning on the outer portions of the leaf while the base of the leaf will still have some normal green color. / Photo Credit: Wisconsin DNR

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

Oak wilt symptoms are active right now, but so are several other oak issues that may be mistaken for oak wilt.

Issues including Tubakia leaf spot, mite damage and leaf scorch are all causing problems in northern Wisconsin and may be mistaken for oak wilt.

Continue reading “Oak Leaf Issues That Are Not Oak Wilt” →