Leaves are down, temperatures are cooler, and that means it’s prime time for pruning oak trees, which can be infected by the oak wilt fungus if they’re pruned during the high-risk period April 15-July 15.

“Beetles that can carry the disease from tree to tree are not very active now, and the trees are not vulnerable to infection,” said Simeon Wright, forest health specialist with the DNR Forest Resources Division. The beetles are attracted to fresh bark damage or wounds where tree limbs have been removed.

Firewood can harbor the fungus, too. If you suspect your firewood is infected, burn it, chip it or debark it before April. Once the wood has been dried over a year and/or all bark loosens, it can no longer spread oak wilt.

“Not moving potentially infected oak firewood into areas that are free of oak wilt is critical to protecting our oak trees,” Wright said.

Oak wilt, identified in the 1940s, is widespread across Michigan’s Lower Peninsula and along the Wisconsin border in the Upper Peninsula. Red oaks are most susceptible and can die within weeks of infection. These trees have leaves with pointed tips and include black oak, northern red oak and northern pin oak. Trees in the white oak group have rounded leaf edges and are less susceptible. Affected trees will suddenly wilt from the top down, rapidly dropping leaves, which can be green, brown or a combination of both colors.

If you suspect oak wilt:

Report infections at Michigan.gov/ForestHealth.

Contact a DNR specialist at DNR-FRD-Forest-Health@Michigan.gov or 906-203-9466.

Verify an oak wilt infection with Michigan State University’s Diagnostic Clinic. Go to PestID.MSU.edu or call 517-355-4536.

Visit MichiganOakWilt.org for a listing of oak wilt-qualified experts.

Learn more about invasive species and diseases at Michigan.gov/Invasives.

Questions? Contact Simeon Wright at 906-203-9466.

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