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Deadly Oak Tree Disease Confirmed in Forest County

Contact(s): Linda Williams, DNR forest health specialist, 920-360-0665, Linda.Williams@wisconsin.gov
October 8, 2019



Leaves first appear brown or water-soaked near the edges before rapidly wilting and dropping from the tree.  - Photo credit: DNR
Leaves first appear brown or water-soaked near the edges before rapidly wilting and dropping from the tree. Photo credit: DNR Forest Health

CRANDON, Wis. - The Wisconsin Department of Natural Resources has confirmed that oak wilt, a deadly disease in oaks, was found in Forest County for the first time.

The DNR tested wood samples taken from two red oak trees in the town of Lincoln, just north of Lake Lucerne.

"This find is particularly concerning given the rarity of the disease in this part of the state," said DNR Forest Health Specialist Linda Williams.

Oak wilt is commonly found in the southern two-thirds of the state and is creeping north. Much of northern Wisconsin remains free of oak wilt, however, making it essential to prevent further spread of the disease.

Leaves of infected trees rapidly wilt and drop to the ground in summer. - Photo credit: DNR Forest Health
Leaves of infected trees rapidly wilt and drop to the ground in summer.Photo credit: DNR Forest Health

Oak wilt is a fungal disease that kills thousands of oak trees each year in forests, woodlots and urban areas. This disease can even attack and kill healthy trees. It does this by plugging up the areas in the tree where water moves, slowing the water down and causing the leaves to wilt and fall off.

Prevent the Spread of Oak Wilt to Healthy Trees
Oak wilt is introduced to new areas either through the transport of infected firewood or through sap-feeding beetles that are attracted to wounds on oak trees. When a wounded tree is also infected with oak wilt, these beetles become a pathway for oak wilt to spread from tree to tree.

After a tree is infected, oak wilt spreads between neighboring trees through interconnected roots. This type of spread is difficult to manage, so preventing the introduction of oak wilt is extremely important. To avoid oak wilt becoming established in the first place, review the following recommendations:

  1. Avoid pruning or injuring oak trees from April 1 through July 15 (in northern Wisconsin, this period begins April 15). This is when the disease and the sap-feeding beetles are most likely to spread.
  2. If oaks are removed, pruned or damaged during this time, seal the wounds with a water-based (latex) paint or pruning sealer.
  3. Keep firewood local and let the wood age in place for at least a year or until the bark is loose. Learn more about firewood at the DNR firewood webpage.

"Infected trees start to wilt and drop green or partially green leaves in late summer," said Williams. "These are not the brown, dry leaves you see in autumn. They fall rapidly from the tree, with a tree losing most of its leaves within a few weeks of symptoms becoming visible."

The University of Wisconsin's Plant Disease Diagnostic Clinic can help verify the presence of oak wilt and will test samples for a fee. Questions can be directed to the clinic at 608-262-2863 or bdh@plantpath.wisc.edu.

Local DNR urban forestry coordinators have information about grants to help combat oak wilt at the community level. Individual property owners can contact their municipal forester or their DNR forest health specialist with questions or concerns.

To learn more about oak wilt, visit the oak wilt page of the DNR website. The YouTube video offers a brief introduction to the disease, its impacts and ways to prevent its spread.

Last Revised: Tuesday, October 08, 2019

Contact information

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