Disease

Thousand Cankers Disease Update

Posted on by brenna.denamur

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

Upward view of a large, leafless black walnut tree.

Black walnut is one of Wisconsin’s healthiest, least threatened tree species. Photo: Wisconsin DNR

Once in a while, the Wisconsin DNR Forest Health Team gets to deliver good news about an emerging insect or disease issue!

Recent research suggests that thousand cankers disease of walnut is not the threat we initially feared when cases appeared for the first time in the eastern U.S. in 2010. Thousand cankers disease is caused by walnut twig beetles carrying a fungal pathogen. The disease has yet to be detected in Wisconsin.

Following its arrival in the eastern United States, the insect’s populations declined. Many stressed urban trees recovered after drought conditions subsided in the impacted areas, and forest trees have fared even better than their urban counterparts. Additionally, walnut twig beetles don’t enjoy Wisconsin winters, as mortality begins in the low single digits Fahrenheit. Perhaps this is why we have not yet found the walnut twig beetle in Wisconsin.

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Help Protect Oak Trees From Oak Wilt

Posted on by brenna.denamur

Contact: Paul Cigan, DNR Forest Health Specialist

Paul.Cigan@wisconsin.gov or 715-416-4920

As April brings a high risk of the often-fatal oak wilt disease, the Wisconsin Department of Natural Resources (DNR) recommends not pruning or cutting oaks from April through July.

A large oak tree in a wooded area has fresh wounds from branches being sawed off.

Do not prune, cut or wound oaks April through July.
Photo: Linda Williams

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Prune Oak Trees In Winter To Help Prevent Oak Wilt

Posted on by brenna.denamur

By Kyoko Scanlon, DNR Forest Pathologist, Fitchburg, Kyoko.Scanlon@wisconsin.gov; and Paul Cigan, DNR Forest Health Specialist, Hayward, Paul.Cigan@wisconsin.gov

Person uses branch cutters to prune oak tree with brown leaves during the winter.

Prune oak trees during winter when oak wilt disease-carrying insects are inactive. Photo credit: Wisconsin DNR

It’s pruning season! If your trees need to be pruned, now it the time to do it. Come April, there’s high risk of harmful pests spreading tree diseases such as oak wilt.
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Diplodia Shoot Blight vs. Red Pine Shoot Moth

Posted on by patricialindquist

By Todd Lanigan, DNR Forest Health Specialist, Eau Claire, Todd.Lanigan@wisconsin.gov or 715-210-0150

Scattered damage to new red pine shoots has been observed across many counties this summer. With the intermittent rains during the summer, the first thought was that Diplodia shoot blight, a fungal disease, was causing the damage. Upon a closer look, some of the shoot mortality is caused by the red pine shoot moth. From a casual glance, these two problems will look the same, so you really need to take a closer look. 

If Diplodia causes the shoot mortality, the shoot usually forms a shepherd’s crook. And, in time, you will find the fungal fruiting bodies on the needles, especially if you look under the needle sheath (covering) at the base of the needles.

Shepherd’s crook caused by Diplodia shoot blight. Photo Credit: Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org

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White Pine Branch Tips Red And Wilting

Posted on by patricialindquist

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

White pine trees in many counties in northeast and northcentral Wisconsin have developed rusty-colored wilting needles on outer branch tips scattered throughout the tree’s crown. These dead branch tips are associated with the feeding by white pine bast scale. The scale is a tiny insect that inserts its straw-like mouthpart into the twig to suck sap from the outer layers of phloem called bast. Damage has been observed on trees over 20 feet tall this year. 

Branch tips on this white pine indicate a problem with bast scale and the disease Caliciopsis. Photo Credit: Wisconsin DNR

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Oak Leaves Turning Brown? There Are Several Reasons This Year.

Posted on by patricialindquist

Written 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 symptoms. Issues including Tubakia leaf spot, Botryosphaeria canker, kermes scale damage and mite damage are all causing problems and may be mistaken for oak wilt.

Oak Wilt Leaf Symptoms

Trees in the red oak group (those with points on their leaves) that became infected with oak wilt in the spring will suddenly start to drop their leaves in July and August. Trees that were infected later in the high-risk period (April 15 – July 15 in northern Wisconsin) may start to drop their leaves later, in September or even into October.

Leaves dropping from oak wilt trees can be fully green, tan or a water-soaked, greenish color away from the petiole (leaf stem). There will often be an area that is still green near the petiole, even though the leaf has fallen to the ground. Wilting leaves typically start near the top of the tree and progresses downwards.

Recommended control measures depend on if you have just one tree actively wilting (and no others have died in past years) or if you are dealing with established pockets that have been present for more than a year. Contact your regional forest health specialist to discuss these control options if you think you have oak wilt.

Leaves dropping from trees dying from oak wilt often are brown or water-soaked on the outer portions of the leaf with green still found near the base of the leaf. Photo Credit: Wisconsin DNR

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Heterobasidion Root Disease (HRD) Found In Fond Du Lac And Racine Counties

Posted on by patricialindquist

By Bill McNee, DNR Forest Health Specialist, Oshkosh, bill.mcnee@wisconsin.gov or 920-360-0942

Heterobasidion root disease (HRD), formerly known as annosum root rot, was recently found in Fond du Lac and Racine counties for the first time. Thinned pine stands were surveyed by DNR forestry staff in four eastern counties where the disease had not been previously found (Fond du Lac, Manitowoc, Racine and Winnebago counties).

Counties where Heterobasidion root disease (HRD) has been found as of August 2021 are shown in green.

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Oak Wilt Symptoms Visible Now

Posted on by patricialindquist

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

Symptoms of oak wilt are showing up. Look for leaves that suddenly wilt and drop from the tree. Oak wilt is a non-curable, fungal disease specific to oaks. Trees in the red oak family will die quickly from this disease, while trees in the white oak family will die more slowly, with a branch or portion of the crown becoming infected. 

This tree is actively wilting from oak wilt infection and will drop most of its leaves within about 4-6 weeks.

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Balsam Fir Needle Rust

Posted on by patricialindquist

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

Balsam fir needle rust is infecting current year needles on balsam fir trees in north-central Wisconsin. Balsam fir needle rust has white pustules that emerge from the lower surface of infected needles. Infected needles will turn yellow and the combination of white pustules and yellow needles gives the trees a pale, ghostly appearance from a distance.

Bright yellow needles are infected with balsam fir needle rust.

Bright yellow needles are infected with balsam fir needle rust.

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Oak Wilt Seasonal Harvesting Opportunities Web Map

Posted on by patricialindquist

By Paul Cigan, DNR Forest Health Specialist

The Forest Health Team has just launched an interactive web map showing areas where seasonal oak harvesting opportunities and restrictions exist within the state. The map provides users with general geographical information on the presence and seasonality of oak wilt restrictions to support decisions concerning the application of the Oak Harvesting Guidelines [PDF] during timber management planning and establishment. As a highlight, areas that favor flexibility in the application of the seasonal harvesting restrictions — based on the nearest known detection of oak wilt — are displayed on the map. If you have any questions about this map, please contact your regional Forest Health specialist.

Oak Wilt Seasonal Harvesting Opportunities Web Map