Help Protect Oak Trees From Oak Wilt

Posted on 4-08-2021

The DNR Recommends Not Pruning Until After July

April brings a high risk for the often-fatal oak wilt disease across the state, and as a result, the Wisconsin Department of Natural Resources (DNR) recommends not pruning or cutting oak trees from April through July. What you can’t see can kill a tree.

Oak wilt is widespread in southern Wisconsin, but it is still a new and uncommon disease in much of northern Wisconsin.

As spring draws property owners outdoors to start seasonal yard maintenance and cleanup projects, when it comes to the health of oaks trees, keeping those chainsaws and trimming tools a safe distance will go a long way to ensure that your trees stay healthy for many more spring seasons to come.

Pruning and cutting oaks in spring and early summer leaves them vulnerable to oak wilt, which rapidly kills trees in the red oak group and weakens those in the white oak group.

Any damage during this time, including broken branches caused by storms, exposes living tree tissue beneath the bark and provides an opportunity for the oak wilt fungus to attack the tree.

Tree paint or wound dressing is not normally recommended on pruned or wounded surfaces, but for damaged oaks a light application of these products immediately, if possible within 15 minutes, may be the only defense against oak wilt infection from April through July. Wounds are not susceptible to oak wilt after 72 hours.

It should be noted that although overland infection can occur in mid-July, it is not common. To be very cautious, avoid wounding oaks from April through October 1st.

As of January 31st, the DNR had received reports of oak wilt in all Wisconsin counties except Ashland, Iron, Forest, Taylor, Door, Kewaunee, Calumet and Manitowoc counties. Several of these counties contain the highest abundance of healthy and productive oak forests in the state. Taking recommended precautions will help keep them that way for years to come. Check with your municipality to find out if they have their own oak wilt ordinances that you should follow as well.