Disease

Anthracnose Infecting Hardwood Leaves

Posted on by janness

By Michael Hillstrom, DNR Forest Health Specialist; Michael.Hillstrom@wisconsin.gov
and Abby Krause, DNR Urban Forestry Coordinator; Abigail.Krause@wisconsin.gov

Oak leaves infected with anthracnose.

Anthracnose is a common disease of hardwood trees during cool, wet spring seasons. Some parts of Wisconsin have been cooler and wetter than others this spring, so anthracnose damage may be patchy.

Ash, maple, white oak, sycamore and walnut are the most commonly impacted tree species. Each species has its own species of anthracnose that infects it, but if weather conditions are right, then we tend to see damage on multiple species. Continue reading “Anthracnose Infecting Hardwood Leaves” →

Watch For Oak Wilt Symptoms

Posted on by akabelowsky
A wide-angle photo showing an oak tree in the center that died rapidly from oak wilt during the summer of 2024.

An oak tree (center) that died rapidly from oak wilt during the summer of 2024. / Photo Credit: Wisconsin DNR

By Michael Hillstrom, Wisconsin DNR Forest Health Specialist
Michael.Hillstrom@wisconsin.gov or 608-513-7690

Oak wilt symptoms typically begin to appear in southern Wisconsin in late June and in northern Wisconsin during July.

Watch for browning leaves, starting at the top of the canopy and progressing downward. Most leaves will fall from infected trees as they die, typically within two to four weeks.

Continue reading “Watch For Oak Wilt Symptoms” →

What’s That Under The Bark Of Red Pines?

Posted on by akabelowsky
A close-up photo showing pitch blobs near the base of a red pine, indicating attack by red turpentine beetle.

Pitch blobs near the base of a red pine indicate attack by red turpentine beetle. / Photo Credit: Linda Williams, Wisconsin DNR

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

Red turpentine beetle and pine root collar weevil are the most common insects found attacking near the base of red pine trees in Wisconsin, whether near ground level or just below ground level.

Here are some tips on identifying and controlling these pests.

Continue reading “What’s That Under The Bark Of Red Pines?” →

Red Pine And Hemlock Needles Suddenly Looking Brown

Posted on by akabelowsky
A photo showing hemlock needles affected by winter desiccation that have started browning at the needle tips and moving inward, sometimes killing the entire needle.

Hemlock needles affected by winter desiccation will start browning at the needle tips and move inward, sometimes killing the entire needle. / Photo Credit: Linda Williams, Wisconsin DNR

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

During the winter months, warm or sunny weather can wreak havoc on evergreen trees.

Conifers such as hemlock, pines and fir can lose moisture from their needles during the winter. If too much moisture is lost, those needles can quickly turn yellow or brown once the weather warms up in the spring.

Extensive browning of needles on hemlock — sometimes more than 50 percent of the needles – was observed in scattered areas of Oneida and Bayfield counties by the second week of April. The brown needles eventually dropped from the trees, leaving the remaining foliage looking very thin. Buds on the trees appeared viable, and the trees should break bud as normal.

Continue reading “Red Pine And Hemlock Needles Suddenly Looking Brown” →

Rotstop® C No Longer Available In North America

Posted on by akabelowsky
Photo of a worker manually applying fungicide, imbued with blue dye, to a freshly cut tree stump to fight the spread of fungal diseases such as Heterobasidion root disease.

A worker manually applies fungicide, imbued with blue dye, to a freshly cut tree stump to fight the spread of fungal diseases such as Heterobasidion root disease. / Photo Credit: Wisconsin DNR

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

The manufacturer, Lallemand Plant Care, recently decided to remove Rotstop® C fungicide from the North American market.

As a result, the product is no longer available for purchase in North America. If you already have the product and have stored it in an appropriate space, you may still use it as a preventative treatment for Heterobasidion root disease (HRD) as long as the expiration date has not arrived.

Continue reading “Rotstop® C No Longer Available In North America” →

Columbian Timber Beetle Fact Sheet Debuts

Posted on by akabelowsky
Photo showing staining, in the shape of a many-pointed star, evident in the cut ends of silver maple logs.

Staining, in the shape of a many-pointed star, is evident in the cut ends of silver maple logs. / Photo Credit: Chris Firgens, Oconto County Forest

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

Columbian timber beetle (Corthylus columbianus) is an ambrosia beetle native to the eastern United States.

In Wisconsin, we have had reports of Columbian Timber Beetle (CTB) attacking silver maple in the northeastern and lakeshore areas of the state, dating back to the early 1990s. The insects have caused significant staining from repeated attacks. In southern Wisconsin, CTB can attack oaks to a lesser degree, including bur, northern red and white oak.

Continue reading “Columbian Timber Beetle Fact Sheet Debuts” →

UW-Madison’s Raffa Talks Trees’ Natural Defenses

Posted on by akabelowsky
Photo of Ken Raffa, professor emeritus with the University of Wisconsin-Madison Department of Entomology.

Ken Raffa, professor emeritus with the University of Wisconsin-Madison Department of Entomology. / Photo Credit: University of Wisconsin-Madison

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

Do you pity the poor tree, forced to stand defenseless against the ravages of insect pests, fungi and disease?

Then, you have not listened to Dr. Ken Raffa discuss the impressive natural defenses trees have developed.

Raffa, a professor emeritus with the University of Wisconsin-Madison’s Entomology Department, recently appeared on Proforest Podforest podcast to discuss the topic “Inside the Tree’s Natural Defense.”

Continue reading “UW-Madison’s Raffa Talks Trees’ Natural Defenses” →

Resources to Help Urban Foresters Set And Meet Tree Diversity Goals

Posted on by janness

By Shahla Werner, Urban Forestry Council Member and Department of Agriculture, Trade and Consumer Protection Plant Protection Section Manager

Urban foresters are increasingly aware of the importance of tree species, age and size diversity to ensure resilient tree canopy and all the associated benefits in their communities. The 20-10-5 rule, which specifies that no more than 20% of trees planted should be from one family, no more than 10% from one genus and no more than 5% from one species (including cultivars), can be helpful in setting tree diversity goals. Applying these guidelines can provide urban forests some protection against huge losses caused by invasive forest pests. Continue reading “Resources to Help Urban Foresters Set And Meet Tree Diversity Goals” →

Watch For Oak Decline And Mortality This Summer

Posted on by akabelowsky
Oak decline and mortality at Big Foot Beach State Park in 2024.

Oak decline and mortality at Big Foot Beach State Park in 2024. / Photo Credit: Wisconsin DNR

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

Oak decline and mortality continue to be an issue in Wisconsin, and because of the recent droughts and spongy moth outbreak, we expect these impacts to become more widespread this summer.

Forest decline is the progressive loss of tree and stand vigor and health over several years without obvious evidence of a single causal factor. Typically, trees die in a scattered fashion across a large area over several years. The additional stress from defoliation can result in pockets of heavy oak mortality, particularly on dry, sandy sites and steep, rocky ridges and hills.

Continue reading “Watch For Oak Decline And Mortality This Summer” →

Spring Brings Opportunities To Protect Oak Trees

Posted on by akabelowsky
A photo of an oak tree with a branch that has been pruned, but not treated with protective paint to prevent infection with oak wilt.

Pruning, cutting, or wounding oaks during April through July leaves them vulnerable to oak wilt. / Photo Credit: Paul Cigan, Wisconsin DNR

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

With warmer spring weather fast approaching, the Wisconsin Department of Natural Resources (DNR) recommends protecting oaks from the often-fatal disease, oak wilt, by refraining from pruning, cutting or injuring oak trees from April through July.

Oak wilt is a serious disease that kills trees in the red oak group (including pin oak, northern red oak and black oak) and weakens those in the white oak group (bur oak, swamp white oak, white oak and English oak).

Continue reading “Spring Brings Opportunities To Protect Oak Trees” →