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Protect oak trees from oak wilt by waiting until after July to prune

Published by Central Office March 21, 2017

Contact(s): Don Kissinger, DNR urban forester (Wausau), 715-359-5793, Don.Kissinger@wisconsin.gov or Paul Cigan, DNR plant pest and disease specialist (Hayward) 715-416-4920, Paul.Cigan@Wisconsin.gov.

MADISON - To protect oak trees and help prevent oak wilt, the Wisconsin Department of Natural Resources advises people to avoid pruning oaks on their property from April through July.

Spring and early summer pruning makes oak trees vulnerable to oak wilt, a fatal fungal disease. Any tree damage during this time creates an opening that exposes live tree tissue and provides an opportunity for the oak wilt fungus to infect the tree.

Just 15 minutes
Just 15 minutes could be enough time for beetles that are carrying oak wilt spores to land on a fresh wound and infect a tree.
Photo Credit: George W. Hudler, Cornell University

"Just 15 minutes could be enough time for beetles that are carrying oak wilt spores to land on a fresh wound and infect your tree," said Paul Cigan, DNR forest health specialist in Hayward.

Property owners with oak trees are encouraged to check with their municipality to find out if there are local oak wilt ordinances.

The use of tree paint or a wound dressing is not normally recommended on pruning cuts or wounded surfaces on most trees. But for damaged oaks, these products are recommended from April through July. An immediate light painting of wounds on oak trees during this time helps protect against the spread of oak wilt by beetles.

Don Kissinger, a DNR urban forester in Wausau, said there are also other important reasons to avoid pruning deciduous trees in spring beyond concerns about oak wilt.

"Spring is the time when tree buds and leaves are growing, leaving the tree's food reserves low," Kissinger said. In general, the best time to prune trees is in winter.

It's worth protecting

Oak wilt and other diseases also move easily on or in firewood logs year-round. To protect trees in general, don't move firewood long distances, or only use firewood labeled as Wisconsin certified.

Oak wilt is found in all Wisconsin counties except Ashland, Bayfield, Calumet, Door, Douglas, Forest, Iron, Kewaunee, Manitowoc, Sheboygan and Taylor counties. Several of these counties have the highest abundance of healthy and productive oak forests in the state. Taking recommended precautions with living oak trees and keeping firewood local to prevent the spread of oak wilt will help keep them that way for years to come.

More information is available online. Visit the DNR website, dnr.wi.gov, and search for "oak wilt" or "firewood." Additional information about proper pruning techniques is available from community foresters or by searching for "tree pruning."

Last Revised: Tuesday, March 21, 2017

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