MADISON, Wis. – The Wisconsin Department of Natural Resources (DNR) reminds you that now is the time to prune your oak trees as there’s high risk of harmful pests spreading tree diseases such as oak wilt come April. Oak wilt is Wisconsin’s most destructive oak disease, killing thousands of healthy trees annually. It’s common in the lower two-thirds of the state and spreads farther north each year.

It is ideal to prune trees in the winter since branch damage or weak branch structure is more visible, and pests that cause harmful tree diseases are inactive in cold temperatures. Oak wilt is one such disease that spreads through tiny sap-feeding beetles attracted to open wounds on trees.

“What’s encouraging about oak wilt is that preventing and slowing its spread takes only the most basic measures,” said Paul Cigan, DNR Forest Health Specialist.

Cigan says Wisconsin residents should only prune trees in winter. Pruning oaks during April through July places them at the greatest risk for oak wilt infection and should be avoided when possible.

Cigan also suggests keeping firewood transport local and consulting a certified professional if you suspect oak wilt by finding oaks with sudden, mid-to-late summer leaf drop.   

Prune young trees to establish a central trunk, proper trunk taper and good branch structure and spacing. Prune older trees to remove dead or hazardous limbs. In addition, it’s recommended to prune landscape trees throughout their lifetime to maintain strong structure and remove dead wood.

Follow the DNR’s Oak Harvesting Guidelines to reduce risk of oak wilt while oak harvesting in a forest setting.

Learn more about oak wilt on the DNR website.

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