(Editor’s Note: The following article was submitted by the Sherburne Soil & Water Conservation District).

Oak wilt is a fungal disease currently found in central and southeastern Minnesota that kills thousands of oak trees every year. It most severely affects the red oak group, including northern red oak and northern pine oak; the white oak group is less susceptible but not immune. 

The disease spreads in two ways: through root grafts between similar species, and over land carried by oak sap beetles carrying fungal spores from tree to tree. The sap beetles are attracted to the chemicals produced by fresh wounds in trees, so we recommend not pruning oaks in the spring and summer. If wounded oak trees are visited by these fungus-contaminated beetles, oak wilt spreads. 

The high-risk season of oak wilt begins when the weather warms up enough to make the sap-feeding beetles active (typically April). The high-risk oak wilt season will run through mid-July. 

To see the current oak wilt risk status, check the University of Minnesota Oak Wilt page at www.extension.umn.edu.  If you suspect your oak tree has oak wilt, you should get an accurate diagnosis of the disease before taking any control action. Contact an experienced tree care professional or consult the University of Minnesota’s Plant Disease Clinic.