Red pine damaged by the April 2nd, 2026, ice storm in central Wisconsin. / Photo Credit: Wisconsin DNR
By Michael Hillstrom, DNR Invasive Forest Pest Coordinator, Fitchburg
Michael.Hillstrom@wisconsin.gov or 608-513-7690
Spring 2026 has seen a variety of tree stress events. Wisconsin trees have experienced snow and ice damage, severe storms that resulted in wind, hail and flood damage and swings in temperatures that brought leaf out and subsequent frost damage.
By Bill McNee, Forest Health Specialist, Oshkosh
Bill.McNee@wisconsin.gov
A spongy moth caterpillar feeds on a leaf. / Photo Credit: Wisconsin DNR
Property owners are encouraged to monitor their trees for spongy moth larvae and damage this summer to determine whether control measures are needed.
Property owners who have oak, birch, crabapple, aspen, willow and linden (basswood) trees should be particularly watchful because the caterpillars of this invasive insect prefer these species.
However, they will feed on many other kinds of trees and shrubs.
Continue reading “Watch For Spongy Moth Caterpillars And Tree Damage This Summer”
A bag of Tim-bor Professional, a borate-based chemical that fights Heterobasidion root disease. / Photo Credit: Wisconsin DNR
By Kyoko Scanlon, Forest Pathologist, Fitchburg
Kyoko.Scanlon@wisconsin.gov
People who have been dealing with Heterobasidion Root Disease (HRD) may be familiar with the product name “Cellu-Treat®.” It has been used to treat fresh cut stumps to prevent HRD.
But Cellu-Treat® is not the only chemical available for HRD. Another borate-based chemical, Tim-bor® Professional, can also be used legally for the same purpose in Wisconsin. Both products are manufactured by Nisus Corporation, and their labels are almost identical (Cellu-Treat label, Tim-bor label).
Continue reading “Fungicide For HRD Stump Treatment Available In Smaller Size”
Japanese honeysuckle climbing up nearby trees. / Photo Credit: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
By Carter Hellenbrand, DNR Invasive Plant Field Specialist, Fitchburg
Carter.Hellenbrand@Wisconsin.gov
Note: This is the first installment in the Forest Health News “Invasives Spotlight” series, a monthly series of Forest Health News articles.
Many people recognize honeysuckle as a fast-spreading invasive shrub that can quickly displace native vegetation. But did you know that some honeysuckles exist as a vine?
Japanese honeysuckle (Lonicera japonica) is an invasive perennial vine that can grow to a length of 80 feet or longer. Birds will often eat and disperse the berries the vine produces, allowing for the creation of new populations.
Cracked bark and wood creates a long vertical wound typical of the phenomenon commonly called “exploding trees.” / Photo Credit: Wisconsin DNR
By Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665
This past winter, “exploding trees” went viral on social media. Many news outlets followed up with a more realistic explanation of the dramatically named phenomenon, pointing out that while the bitter cold can cause sudden cracks to form on trees, the trees don’t truly explode.
But what happens to those damaged trees as we warm up and move into the growing season?
Paul Cigan, the Wisconsin DNR’s Forest Health specialist for the Northwest zone. / Photo Credit: Wisconsin DNR
By Wisconsin DNR
A list of public appearances planned by Wisconsin Department of Natural Resources (DNR) Forest Health specialists over the coming weeks:
Continue reading “DNR Forest Health Specialists Plan Appearances”
A putty knife, plastic knife or similar object can be used to gently scrape spongy moth egg masses into a cup of soapy water. The water can be discarded after two days. / Photo Credit: Wisconsin DNR
By Bill McNee, DNR Forest Health Specialist, Oshkosh
Bill.McNee@wisconsin.gov
The Wisconsin Department of Natural Resources (DNR) encourages property owners to examine their trees for spongy moth egg masses and determine whether control measures are needed this spring.
Property owners who have oak, birch, crabapple, aspen, willow and linden (basswood) trees should be particularly watchful because the caterpillars of this invasive insect prefer these species. However, they will feed on many other kinds of trees and shrubs.
Continue reading “Look For Spongy Moth Egg Masses And Take Action”
A University of Wisconsin-Madison Extension online tool provides users localized information about the estimated emergence status of the two most important insects that transmit oak wilt in Wisconsin. / Graphic Credit: University of Wisconsin-Madison Extension
By Kyoko Scanlon, DNR Forest Pathologist, Fitchburg
Kyoko.Scanlon@wisconsin.gov
In 2025, oak wilt was detected for the first time in Hughes Township, Bayfield County, a northern Wisconsin location where oak wilt remains uncommon. There were no new county finds in 2025.
Based on the findings in 2025, the maps in the Oak Harvesting Guidelines To Reduce The Risk Of Introduction And Spread Of Oak Wilt (the oak wilt guidelines), oak wilt fact sheet and were updated. The maps in the oak wilt guidelines are good through the end of 2026.
A fungal pressure pad formed on the outside of the sapwood underneath the bark of an infected tree. The pad will create cracks in the bark, where beetles can enter and visit the pad and become covered in spores. They will then leave and move on to infect new trees through open wounds. / Photo Credit: Wisconsin DNR
By Alex Hornung, DNR Forest Health Specialist, Plover
Alexandra.Hornung@wisconsin.gov or 715-340-3810
It is again that time of year to pause operating in oak stands or pruning oak trees during the high-risk period for oak wilt, which begins in April. The high-risk period begins April 1 in the South, April 15 in the North, and ends in both zones on July 15.
The high-risk period is determined by when the beetles that carry the fungus that causes oak wilt have emerged for the year and when they are carrying the highest number of fungal spores. When wounds are created by logging operations or other activities that expose sapwood, the beetles carry the fungus to the wounded tree, and the disease process begins.
Continue reading “Oak Wilt High Risk Period Quickly Approaches”
The cover of the 2025 Wisconsin Department of Natural Resources Forest Health Annual Report. / Graphic Credit: Wisconsin DNR
By Art Kabelowsky, DNR Outreach and Communications, Fitchburg
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167
The Wisconsin Department of Natural Resources (DNR) has made its 2025 Forest Health Annual Report ready to view and download.
This year’s edition contains 55 pages of reporting on forest health issues throughout Wisconsin, detailing methods employed by the DNR and other agencies to control pests, diseases and invasive plants.
Continue reading “Forest Health Annual Report Hot Off The Presses”
