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Avoid pruning or wounding oak trees to prevent the spread of oak wilt disease

To help prevent oak wilt, forest health specialists in Minnesota are asking homeowners and landowners to avoid pruning or wounding oak trees in the spring. High risk months in Minnesota are typically April, May and June.

Spring weather promotes the activity of sap-feeding beetles that can transmit the fungus that causes oak wilt disease. Pruning and cutting oaks in the spring months attract the beetles to these trees. The oak wilt disease can be spread through root grafts from an infected tree.    

All species of oaks can become infected in Minnesota, but red oak species like northern red oaks and pin oaks are more seriously affected and can show immediate symptoms. Symptoms in red oaks are the rapid wilting of leaves which can be seen as quickly as two to six weeks after infection.     

Oak leaves turning brown from oak wilt disease
Oak wilt infected tree

“Oak wilt is commonly seen in the Twin Cities metro and southeastern Minnesota,” says University of Minnesota Extension Specialist Matt Russell. “But we’re especially concerned with the disease spreading north and west into Minnesota’s healthy oak forests.”

Avoiding construction activities near oaks also helps. If pruning is absolutely necessary, seal the wound immediately with shellac or water-based paint.

It is also important not to move any firewood from oaks that may have died from oak wilt to other locations. Even if trees have been cut down for firewood, the fungus can survive underneath the bark for several months. 

Read more about oak wilt.

Matt Russell is an Extension forestry specialist based in St. Paul, MN. His research focuses on forest ecosystem health. He teaches forest landowners and natural resource professionals strategies to maintain healthy and productive forests.

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