Minnesota DNR says prune oaks now to avoid oak wilt

St. Paul — The unusually warm winter might leave more than a mark on the record books. It could hasten invasive oak wilt infection risk. Now is the safest time to prune and trim oak trees to prevent the spread of this deadly disease, according to the Minnesota DNR.

Oak wilt, a non-native fungal disease, is spread when sap-feeding beetles become active in warm weather and carry oak wilt spores from one tree to the next. These beetles are attracted to the sap from fresh wounds, such as those made by pruning. Once beetles introduce the fungus, it frequently spreads to neighboring oaks underground through connected roots.

“Don’t wait until after February to trim oak trees – it might be too late,” said Brian Schwingle, DNR forest health coordinator. “Oak wilt is widespread in parts of southeastern Minnesota, and pockets of disease extend to north and west of Brainerd. We can slow this northern progression by pruning oaks now, when the risk of oak wilt transmission is zero.”

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Typically, April through July is the period of highest risk for oak wilt to spread. However, this winter is anything but typical. If late February and early March bring high temperatures approaching 60 degrees for a few consecutive days, sap-feeding beetles will become active much earlier than usual and oak wilt risk will increase. The last time that happened was in 2012.

If people must prune or cut oaks during a riskier period, they can greatly reduce infection risk by immediately applying a pruning paint to the fresh cut or stump. Always check the status of oak wilt risk at the University of Minnesota’s oak wilt in Minnesota website before working on oak trees.

The DNR also cautions homeowners, campers, cabin owners, visitors, and hunters against moving oak firewood, which can spread oak wilt over long distances. Instead, use firewood sourced onsite or certified by the Minnesota Department of Agriculture to prevent transporting oak wilt and other invasive species.

For more details on oak wilt, including identification, prevention, and how best to deal with infected trees and wood, visit the DNR’s oak wilt management webpage.