The Minnesota Department of Natural Resources is reminding Minnesotans that not pruning or cutting oaks from April through July is the simplest way to curb the spread of oak wilt disease.

Oak wilt is a non-native disease that can kill any oak species in Minnesota. Sap beetles spread oak wilt via fungal spores as they move from infected logs or trees to fresh cuts or wounds on healthy oaks. As weather warms, these beetles become very active, making spring and early summer a high-risk time to prune or cut oaks or move infected oak firewood.

After mid-July, the risk of wound infection drops. However, once an oak is infected, the disease spreads down its trunk and through its roots to neighboring healthy oaks.

“Treating oak wilt can be difficult and costly, but fortunately, prevention is simple and cheap,” said Brian Schwingle, DNR forest health program coordinator. “By following simple pruning guidelines and avoiding the highest risk period from April through July, people can limit the spread of oak wilt in their yards, woods and communities.”

The DNR has confirmed oak wilt in 31 Minnesota counties and notes that the disease is slowly spreading north and west. No new counties had confirmed cases in 2025.

The DNR also cautions people not to move fresh oak firewood, which can spread oak wilt over long distances to new areas. Use locally sourced firewood or firewood certified by the Minnesota Department of Agriculture to prevent transporting oak wilt and other invasive species.

More details about oak wilt, including identification, prevention, reporting instructions and mitigation, is on the DNR’s oak wilt management webpage.

Looking for help to address oak wilt or other tree-related concerns? Visit the DNR ‘Hiring an arborist’ webpage for information on hiring a tree care professional.