The Minnesota Department of Natural Resources says winter is the safest time to prune or cut oak trees without risking the spread of oak wilt, a deadly fungal disease that affects all of Minnesota’s oak species.

Oak wilt is spread in part by sap-feeding beetles that move spores from infected trees to fresh wounds on healthy ones. The disease is widespread in east-central and southeast Minnesota and continues to expand north and west.

DNR forest health consultant Brian Schwingle says treatment for oak wilt can be costly, but prevention is often simple — and sometimes free. He says pruning or cutting oaks during the winter months is one of the most effective ways to avoid infection.

The DNR warns that the highest risk of spreading oak wilt occurs from April through July, when beetles are most active. Residents are urged to avoid pruning during that time.

More information on identifying and managing oak wilt is available on the DNR’s oak wilt webpage, along with guidance on hiring certified arborists.