By Michael Hillstrom, DNR Forest Health Specialist
Michael.Hillstrom@wisconsin.gov
A stand of pines shows heavy damage from an ice storm in April 2025. / Photo Credit: Wisconsin DNR
Winter damage can significantly impact the health of trees. Keeping trees healthy through the fall is important for reducing winter stress. Provide water as needed to trees until the leaves start falling (for deciduous trees) or until the ground starts freezing (for conifers).
By Art Kabelowsky, DNR Outreach and Communications
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167
Wisconsin Department of Natural Resources Forest Health team leader Becky Gray (left) and Department of Agriculture, Trade and Consumer Protection Pest Survey and Control Section manager Renee Pinski appear before the Natural Resources Board to discuss tree and forest health issues on Nov. 13, 2025. / Photo Credit: Wisconsin DNR
The spirit of interagency communication was on display during a joint meeting of the Wisconsin Natural Resources Board (NRB) and the Wisconsin Board of Agriculture, Trade and Consumer Protection (Ag Board) on Nov. 13.
The seven-member NRB is the governing body of the Wisconsin Department of Natural Resources (DNR); the nine-member Ag Board governs the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP). Each board sets policies and rules to be followed and enforced by its respective agencies. Members of both boards are appointed by the governor and confirmed by the Wisconsin State Senate.
Continue reading “DNR, DATCP Teams Exemplify Interagency Teamwork”
Woodpecker flecking on the bark of a dying ash tree is visible at Winnebago County Community Park in Oshkosh. Flecking occurs when the birds peck away at the trees to feed on emerald ash borer larvae beneath the bark. / Photo Credit: Wisconsin DNR
By Bill McNee, DNR Forest Health Specialist
Bill.McNee@wisconsin.gov
The Wisconsin Department of Natural Resources (DNR) encourages property owners to watch for woodpecker damage to their ash trees this winter.
Woodpecker damage, often called “flecking,” happens when birds peck away some of a tree’s bark to access the larvae underneath. Flecking is a common early sign that an ash tree might be infested with emerald ash borer (EAB), an invasive insect. EAB is the most damaging threat to Wisconsin trees, killing more than 99% of the untreated ash trees it infests.
Small, white hemlock woolly adelgid eggs are found on the needles of a tree in Bastian, Virginia, in 2017. / Photo Credit: Bill McNee, Wisconsin DNR
By Mike Hillstrom, Forest Invasive Pest Coordinator, Fitchburg
Michael.Hilstrom@wisconsin.gov or 608-513-7690
Hemlock woolly adelgid (HWA) looms as a major threat to Wisconsin’s hemlock trees. As the infestation of these invasive, aphid-like insects spreads in Michigan and other states in the eastern United States, Wisconsin is preparing to respond when it arrives.
HWA is most evident in winter and spring as fluffy, white, woolly balls that are present at the base of hemlock needles. These fluffy, waxy balls cover adult female adelgids and eggs.
Continue reading “Report Invasive Hemlock Insects This Winter”
An arborist uses climbing safety gear to prune an oak tree along a road. / Photo Credit: Wisconsin DNR
By Mike Hillstrom, Forest Invasive Pest Coordinator, Fitchburg
Michael.Hilstrom@wisconsin.gov or 608-513-7690
Winter is an ideal time to perform trimming, cutting and brush removal work on and near trees, especially oak trees.
Winter is the best time to prune because the insects and diseases that attack oak trees, such as oak wilt, are not active. Pruning and other work can be done around oak trees from after the first hard freeze in the fall until the high-risk period for oak wilt begins in April.
Continue reading “Take Advantage Of Mild Winter Days To Prune Trees”
By Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665
Webbing and a collection of frass (caterpillar excrement) around these cones is the web nest of pine webworm. / Photo Credit: Wisconsin DNR
Pine webworm (Pococera robustella) is a native moth whose caterpillars feed on pine needles. In Wisconsin, the caterpillars prefer young jack pine and red pine. A single generation per year occurs in Wisconsin.
Young larvae mine needles, feeding within the needle. Older larvae form a compact web that they fill with small, oval pieces of frass. In early fall, the larvae drop to the ground to pupate and spend the winter.
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”
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 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.
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.
