Despite a cool and snowy spring, oak trees will soon be at risk of oak wilt infection. Oak wilt is an invasive fungal disease that kills all of Minnesota’s oak species. Not pruning or cutting oaks from April through July is the easiest way to prevent the spread, according to the Minnesota Department of Natural Resources.
April is the average start of the period when there is risk of oak wilt infection on fresh cuts or wounds. Spring temperatures can be unpredictable, so the exact date varies. You can use the University of Minnesota Extension’s oak wilt in Minnesota page to find daily updated oak wilt risk for your part of the state.
Oak wilt is spread to new areas by beetles carrying oak wilt spores. These beetles are attracted to fresh wounds on an oak. Oaks can become infected with oak wilt if they are trimmed or damaged in spring and early summer. Once beetles introduce the fungus, it may spread to neighboring oaks underground through connected roots. In recent years, the disease has expanded into northern forests in Crow Wing, Cass, and Pine counties.
“Controlling oak wilt can be very expensive and often requires removing many dying and healthy oak trees to save others on a property,” said Rachael Dube, DNR forest health specialist. “The good news is that by following pruning guidelines, people can reduce spread of oak wilt in their yards, woods, and communities.”
Dube encourages residents to prune and cut oaks in November through February, when there is no risk of oak wilt transmission. If residents must prune or cut oaks before July, they can greatly reduce infection risk by immediately applying a pruning paint to the fresh cut or stump.
In addition to following pruning guidelines, Dube cautions campers, cabin owners, visitors, and hunters not to move infected 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 transporting oak wilt and other invasive species.
For more details on oak wilt prevention and how best to deal with infected trees and wood, visit the DNR’s oak wilt management page.