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April marks the beginning of the high-risk season for oak wilt, so the Minnesota Department of Natural Resources reminds people not to prune oaks from April through July. This is the best way Minnesotans can prevent the spread of the deadly oak wilt disease.

Oak wilt is a nonnative, invasive fungal disease that kills all species of oak in Minnesota. It spreads two ways: above ground by sap-feeding beetles and below ground through connected roots. By avoiding pruning or cutting oaks in spring and early summer, people prevent fungus spread by sap beetles carrying spores from infected trees to fresh cuts.

“Once oak wilt gets stared, controlling the disease is expensive,” said Rachael Dube, DNR northwest region forest health specialist. “The good news is, by following pruning guidelines, people can prevent or reduce the spread of oak wilt in their yards, woods, and communities.” Dube encourages residents to limit pruning to November through February when there is no risk of oak wilt transmission.

One of the DNR’s goals is to halt the overall northward expansion of oak wilt in Minnesota, which in recent years has reached the northern portions of Morrison and Pine counties. In addition to following pruning guidelines, Dube cautions campers, cabin owners and visitors, and hunters not to move firewood. Moving oak firewood can spread oak wilt over long distances. Use locally sourced firewood or firewood with the Minnesota Department of Agriculture (MDA) certified seal to prevent moving oak wilt.

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