Disease

On The Lookout For Oak Wilt Fruiting Bodies

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

Have you ever seen an oak wilt fruiting body? Oak wilt is a fungal disease that kills trees in the red oak group (northern red oak, northern pin oak, black oak and other oaks with points on their leaves). Trees in the white oak group (white oak, burr oak, swamp white oak and other oaks with rounded leaves) are more resistant to the disease, but branches or branch tips can still be killed.

A small crack in tree bark that indicates an oak wilt pressure pad is underneath.

Oak wilt pressure pads can create a crack in the bark, allowing beetles to get into the spores. Photo: Wisconsin DNR

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June To October: Oak Wilt Watch!

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

An image of two red oak leaves that are part brown and part green, symptomatic of oak wilt infection.

Typical browning leaf symptoms of red oak trees infected with oak wilt. Photo: Wisconsin DNR

Now is the time to watch for oak wilt! Symptoms typically 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.

Several management methods are available to contain oak wilt pockets, so consult your local forest health specialist for guidance on your best options.

The forest health team is also working to evaluate new control methods. Rapid response is currently being tested to more formally evaluate if a new oak wilt infection in a single tree can be stopped before it reaches the roots and spreads to nearby oaks. There is observational data that this method works, but more formal tests are desired. Continue reading “June To October: Oak Wilt Watch!”

When It Rains, It Spores! Orange Spore Horns Emerge

By Ethan Wachendorf, DNR Forest Health Lab Technician, Fitchburg, ethan.wachendorf@wisconsin.gov or 608-273-6276

Have you noticed orange, jelly-like growths on cedars this spring? These growths may look like tiny octopus creatures with legs extending all directions, but they’re actually spore horns caused by a fungus.

Orange jelly-like horns extending 1/2 inch long and 1/8 inch in diameter on cedar

Orange jelly-like spore horns caused by cedar-apple rust fungus. Photo: Wisconsin DNR

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White Trunk Rot In Aspen Trees

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

White trunk rot (Phellinus tremulae), sometimes called aspen trunk rot, is a fungus that causes decay columns to form in aspen. The fungus enters the tree through branch stubs, wounds or small dead branches that remain on the tree. Perennial conks, or fungal bodies, then grow from these sites.

A cross section of the trunk of an aspen with significant decay in the center and a fruiting body conk on the side of the wood.

White trunk rot causes decay in aspen trees. Note the conk (fruiting body) from the fungus on the left side of the pic. Photo: Wisconsin DNR

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Spring Cleaning: Storm Damage Cleanup Brings Oak Wilt Risk

By Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665 & Paul Cigan, DNR Forest Health Specialist, Hayward, Paul.Cigan@wisconsin.gov, 715-416-4920.

Spring cleanup is always a busy time in the Northwoods as those with second homes and cabins make the trek northward to prepare for a summer of fun. For many, this will mean cleaning up trees and branches damaged by winter storms.

A forested scene with broken branches at the base of a white pine tree.

Large white pines (pictured here) and young birch growing on forest edges were most heavily impacted by winter’s storms. Photo: Wisconsin DNR

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Thousand Cankers Disease Update

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

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

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

Start the year off by pruning your trees to protect them from harmful pests that emerge after the thaw. Continue reading “Prune Oak Trees In Winter To Help Prevent Oak Wilt”

Diplodia Shoot Blight vs. Red Pine Shoot Moth

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

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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