March 24, 2015
MADISON - To protect oak trees and help prevent oak wilt, state forestry officials advise 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.
Any tree damage during this time creates an opening to expose live tree tissue and provides an opportunity for the oak wilt fungus to invade and establish itself in the tree.
"In general, spring pruning of deciduous trees should be avoided. Spring is the time when tree buds and leaves are growing, leaving the tree's food reserves low," according to Don Kissinger, a Department of Natural Resources urban forester.
The use of tree paint or a wound dressing is not normally recommended on pruning cuts or wounded surfaces on most trees. However, these products are recommended for damaged oaks 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.
"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 Kyoko Scanlon, DNR statewide forest pathologist.
Arborists recommend that pruning may resume in August, however, the risk for disease transmission is lowest if pruning occurs between November and April. Check with your municipality to find out if they have their own oak wilt ordinances that you must follow.
Oak wilt is found in all Wisconsin counties except Ashland, Bayfield, Calumet, Door, Douglas, Forest, Iron, Kewaunee, Manitowoc, Price, Sheboygan and Taylor counties. The disease was confirmed in Washburn County for the first time in 2014.
More information about oak wilt is available online. Search the DNR website, dnr.wi.gov, for keywords "oak wilt". Additional information about proper pruning techniques is available from your community forester, a University of Wisconsin-Extension agent (exit DNR), or search the DNR website, dnr.wi.gov, for a brochure on "tree pruning [PDF]".
FOR MORE INFORMATION, CONTACT: Kyoko Scanlon (Fitchburg) 608-275-3275, Don Kissinger (Wausau) 715-359-5793 or Paul Cigan (Spooner) 715-416-4920