They can be pruned anytime through the middle of summer.
Mar 14, If you have oaks in your landscape that need pruning and you live in an area of Minnesota where oak wilt occurs, pruning must be done before the oak wilt fungus and it's insect vector become active. Oak wilt is a fatal disease of oak trees that can be found in some counties of Minnesota. If you live in an area where oak wilt occurs, it is critical to prune oak trees before the high risk infection period.
Oak trees should be pruned in the winter months when the trees are dormant and beetles are inactive to prevent the spread of oak wilt. Winter pruning is also great for arborists as the harder ground provides them easier access to trees and the bare canopy makes branches easier to see and handle. However, not all trees should be pruned in the late winter or early spring. There are other factors that will.
Oak wilt covers a large area in Minnesota and affects all species of oak trees. Check the DNR website for an up-to-date oak wilt disease map. To manage oak wilt Don't prune oaks from April through July to prevent spread by insects. Stop below-ground spread by cutting root connections. Don't move firewood from oak wilt infected areas.
Sep 21, The University of Minnesota Forestry Department posts the oak wilt risk levels for pruning oaks: high risk in April through June, low risk in July through October, and no risk in November through March. You can safely prune Minnesota oaks in winter and take appropriate precautions as needed to protect the health of your tree. Apr 08, High risk months in Minnesota are typically April, May and June. Spring weather promotes the activity of sap-feeding beetles that can transmit the fungus that causes oak wilt disease.
Pruning and cutting oaks in the spring months attract the beetles to these trees. The oak wilt disease can be spread through root grafts from an infected tree.