Do not prune oaks

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minnesota department of natural resources

Division of Forestry

April 8, 2021

Oak wilt banner

High-risk oak wilt season: Do not prune oaks

Minnesota known range of oak wilt map.

April marks the beginning of the high-risk season for oak wilt. According to the Department of Natural Resources, not pruning oaks from April through July is the best preventative measure to curb the spread of the deadly oak wilt disease.

Image at right: The pink area is the oak wilt high-risk zone and shows the known range of oak wilt in Minnesota as of October 2020.

Oak wilt is a non-native, invasive fungal disease that kills all of Minnesota’s oak species. 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, residents 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 postpone pruning until 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 certified by the Minnesota Department of Agriculture to prevent moving oak wilt.

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More oak wilt info

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.  

Fallen leaf showing oak wilt symptoms.

DNR Forestry forest health unit

DNR Forestry's forest health unit is responsible for surveys, evaluations, and impact assessments of native and invasive forest pests and diseases as well as technical assistance for public and private landowners on tree health issues.

For more information, please contact Val Cervenka, forest health program consultant, at 651-259-5296 /