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March 18, 2014

MADISON - To protect oak trees and help prevent oak wilt, the Department of Natural Resources advises people with oak trees on their property not to prune them from April through July. Spring and early summer pruning makes oak trees vulnerable to oak wilt, a fatal fungal disease of oaks.

oak wilt
Oak trees infected with oak wilt.
DNR Photo by Kyoko Scanlon

In fact, homeowners should take special care and avoid wounding oaks in any way from April through July. Any action that provides an opening into the tree, such as carving initials into the tree, accidentally cutting exposed roots with a lawn mower, or attaching a birdfeeder or clothes line, could provide an opportunity for the oak wilt fungus to invade and establish itself in the tree.

"Pruning deciduous trees in general should be avoided in the spring, as this is the time when tree buds and leaves are growing and food reserves are low," according to Don Kissinger, a DNR urban forester.

Builders and developers also need to be very careful, as many oak wilt infections occur through inadvertent damage during the construction process.

While using tree paint or a wound dressing is not normally recommended on pruning cuts or wounded surfaces on most trees, oaks are an exception from April through July. An immediate light painting of wounds on oak trees is recommended during this time to help protect against the spread of oak wilt by beetles. "Just 15 minutes could be enough time for the beetles to land on a fresh wound and infect your tree," said Kyoko Scanlon, DNR's statewide forest pathologist.

While the risk of spreading oak wilt is low after July, homeowners should avoid pruning or wounding oaks until November, to be on the safe side. Check with your municipality to find out if they have their own oak wilt ordinances that you should follow as well.

Oak wilt is found in all Wisconsin counties except Ashland, Bayfield, Calumet, Door, Douglas, Forest, Iron, Kewaunee, Manitowoc, Price, Sheboygan, Taylor and Washburn counties. The disease was confirmed in Rusk County for the first time in 2013. .

More information about oak wilt and other forest pests is available on the Wisconsin DNR website. Visit and search the words "oak wilt" or "forest health." Additional information about proper pruning techniques is available from your community forester, a University of Wisconsin-Extension agent (exit DNR), or DNR urban forestry coordinators.

FOR MORE INFORMATION, CONTACT: Kyoko Scanlon (Fitchburg) 608.275-3275, Don Kissinger (Wausau) 715.359-5793 or Brian Schwingle (Merrill) 715.536-0889.

Last Revised: Tuesday, March 18, 2014

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