Disease

Fungicide For HRD Stump Treatment Available In Smaller Size

Posted on by akabelowsky

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).

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Take Precautions to Prevent Tick Bites

Posted on by akabelowsky

An adult deer tick looks for a spot to attach. / Photo Credit: Wisconsin DNR

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

Adult blacklegged (deer) ticks are already active this year, as of March 2026. The adults start looking for a host as soon as it warms up to around 40 degrees Fahrenheit.

In Wisconsin, between 20-60 percent of adult ticks are infected with the bacteria that causes Lyme disease. However, the risk of getting Lyme disease is higher with bites from nymphal ticks, which are most abundant in June and July, because they are so tiny and difficult to find. While only 10-28 percent of nymphs are infected with the Lyme disease bacteria in Wisconsin, rapid removal of a tick can reduce the risk of infection because it takes at least 24 hours for the Lyme bacteria to spread.

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Oak Wilt Information Updated

Posted on by akabelowsky
University of Wisconsin-Madison Extension online tool to help with oak wilt decisions.

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.

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Oak Wilt High Risk Period Quickly Approaches

Posted on by akabelowsky
A closeup of a fungal pressure pad under the bark of an oak tree infected with oak wilt.

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.

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Upcoming Training

Posted on by janness

group of people listening to a speaker in the woods* These training opportunities are provided as an information service only and do not constitute an endorsement from the Wisconsin Department of Natural Resources (DNR).

See below for information on training topics and events, including shade trees, fruit trees, chainsaw certification, tree diseases and pests, pruning and public perspectives on trees. Continue reading “Upcoming Training” →

Heterobasidion Root Disease Resources Updated

Posted on by akabelowsky
Heterobasidion root disease fruiting bodies grow on base of tree

A tree shows fruiting bodies of Heterobasidion root disease at the base of its trunk. / Photo Credit: Wisconsin DNR

By Kyoko Scanlon, DNR Forest Pathologist
Kyoko.Scanlon@wisconsin.gov or 608-235-7532

In 2025, Heterobasidion root disease (HRD), a destructive fungal disease, continued to be found in Wisconsin counties where the disease had previously been detected. There were no new county finds in 2025.

Based on the findings in 2025, the maps in the HRD stump treatment guidelines and online viewer have been updated. The 6-mile and 25-mile buffer zone maps in the guidelines are updated annually and good through Dec. 31, 2026.

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Phomopsis, Black Knot Easily Found In Winter

Posted on by akabelowsky
Phomopsis galls are found on branches of a northern red oak.

This northern red oak has many large Phomopsis galls. / Photo Credit: Wisconsin DNR

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

Winter is a great time to admire the structure of trees. When they are without leaves, you can see how the branches are arranged, how large or small the branches are, and if they are fairly straight or contorted. You might also notice some swellings or growths on those branches.

Two types that can really make a statement are Phomopsis and black knot.

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White Pine Blister Rust Can Devastate Young Stands

Posted on by akabelowsky

By Tim Shively, DNR Forest Health Specialist
Timothy.Shively@wisconsin.gov or 608-772-6974

A close-up photo of a white pine blister rust canker as seen on a young white pine tree.

A white pine blister rust canker as seen on a young white pine tree. / Photo Credit: Wisconsin DNR

Eastern white pine (Pinus strobus) has historically held great ecological, cultural and economic value throughout Wisconsin, a tradition which continues today. For more than 100 years, however, it has been threatened by a non-native, invasive fungal pathogen called Cronartium ribicola, or white pine blister rust (WPBR).

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Stumping Heterobasidion Root Disease With Cellu-Treat®

Posted on by akabelowsky
Photo of a freshly cut tree stump after treatment with fungicide to prevent infection with Heterobasidion root disease. The fungicide is dyed blue to help ensure complete coverage.

A freshly cut tree stump after treatment with fungicide to prevent infection with Heterobasidion root disease. The fungicide is dyed blue to help ensure complete coverage. / Photo Credit: Wisconsin DNR

By Tim Shively, DNR Forest Health Specialist, Eau Claire
Timothy.Shively@wisconsin.gov or 608-772-6974

Treating freshly cut conifer stumps is critical to preventing infection by Heterobasidion species, causal agents of Heterobasidion root disease (HRD).

Within this genus, H. irregulare is believed to be the only species in Wisconsin, and it causes the mortality of overstory pine and spruce trees. The DNR has developed comprehensive guidelines to assist landowners, property managers, foresters, and loggers with determining whether stump treatments are necessary to prevent the introduction or spread of HRD at a given site.

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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.

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