Pest

On The Lookout For Oak Wilt Fruiting Bodies

Posted on by brenna.denamur

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

Continue reading “On The Lookout For Oak Wilt Fruiting Bodies” →

June To October: Oak Wilt Watch!

Posted on by brenna.denamur

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!” →

Basswood Thrips: Tiny Terrors Of Basswood Leaves

Posted on by brenna.denamur

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

Introduced basswood thrips are tiny, invasive insects that feed inside tree buds in early spring. Leaves are then deformed when they expand and can look like frost or wind has damaged them.

A long and thin introduced basswood thrips rests on the underside of a small green leaf.

An adult introduced basswood thrips on the underside of an emerging basswood leaf. This photo is enlarged under a microscope. To the naked eye, they appear as tiny black specks on the underside of the leaf. Photo: Wisconsin DNR

Continue reading “Basswood Thrips: Tiny Terrors Of Basswood Leaves” →

White Trunk Rot In Aspen Trees

Posted on by brenna.denamur

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

Continue reading “White Trunk Rot In Aspen Trees” →

EAB Identified For The First Time In Forest And Ashland County

Posted on by brenna.denamur

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

Emerald ash borer (EAB) has been detected for the first time in Forest County in the Town of Armstrong Creek and Ashland County in the City of Ashland. The Forest County detection was most likely a natural expansion of other infestations in Florence and Marinette counties.

Bark has been removed from an ash tree to show EAB tunnels present near the base of the tree.

This Forest County tree was infested with EAB top to bottom. Photo: Wisconsin DNR

The Ashland County detections appear to be isolated infestations likely spread through the transportation of firewood or logs. Several large green ash stands in the City of Ashland show advanced infestation signs.

EAB was first found in Wisconsin in 2008. There are now just seven counties where EAB has not yet been identified. EAB was federally deregulated as of January 2021. In 2018, Wisconsin instituted a state-wide quarantine. This discovery in Forest and Ashland counties will result in no regulatory changes.

Please visit the interactive Wisconsin EAB detections map to see where EAB has been reported. Follow the map’s instructions if you know of an infested area not on the map. Continue reading “EAB Identified For The First Time In Forest And Ashland County” →

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.

Continue reading “Thousand Cankers Disease Update” →

Emerald Ash Borer Found In Bayfield County

Posted on by brenna.denamur

By Paul Cigan, DNR Forest Health Specialist

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

Emerald ash borer (EAB) has been discovered in Bayfield County for the first time in both the city of Bayfield and Bayview township to the south. This marks the 63rd out of Wisconsin’s 72 counties to have an EAB discovery since its initial detection in 2008.

Dead white ash with woodpecker damage in a park

Figure 1: First known infested ash tree in Bayfield County with characteristic woodpecker damage (i.e., flecking).
Photo: Wisconsin DNR

Several white ash trees (Fig 1.) were observed in and around a roadside park in the city of Bayfield, and larval specimens were subsequently lab-confirmed. In Bayview, a black ash swamp had several infested black ash (Fig 2). 

After introduction, EAB populations remain low for at least several years as most larvae in newly infested, healthy ash require two years to complete their life cycle. The abundance of healthy ash at each site suggests EAB populations have remained low since their introduction at least three years ago. However, EAB will kill ash more quickly as beetle numbers mount and more larvae transform from egg to adult in a single year. Unfortunately, many ash in the area are expected to die within four to seven years based on detection-to-impact timeframes observed from the Superior and Duluth area and research conducted in midwestern states. Continue reading “Emerald Ash Borer Found In Bayfield County” →

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

Continue reading “Help Protect Oak Trees From Oak Wilt” →

Squirrel Damage Mayhem

Posted on by brenna.denamur

By Linda Williams, DNR Forest Health Specialist, Woodruff

Linda.Williams@wisconsin.gov or 920-360-0665

Finger pointing at tooth marks on the wood of a maple that squirrels stripped of bark.

Narrow grooves are left when squirrels chew the bark off a young tree or a branch.
Photo: Wisconsin DNR

In late winter, it’s common to see tree branches that have been freshly stripped of their bark. Damage can be extensive where entire branches, and sometimes entire small trees, can be stripped of bark. This damage, believe it or not, is from squirrels! While primarily found on sugar maples, you can also find squirrel damage on red maples and the occasional oak. So far this year, the damage has been noted in Langlade, Shawano, Oneida and Vilas Counties. 

On sunny days, the pale wood of branches where the bark has been stripped off stands out in the forest. This type of feeding can remove enough bark to girdle the branches or the main stem, causing the tree to die from that point to the end of the branch. Branches that are not entirely girdled will continue to grow, and callus tissue will begin to grow over the wounds. If branches are nearly girdled, they may leaf out in the spring only to have the leaves suddenly wilt and die as hot weather hits because the tree can’t move enough water to keep the leaves alive. Continue reading “Squirrel Damage Mayhem” →