Pruning trees in winter can help reduce the spread of oak wilt
Published: January 8, 2013 by the Central Office
MADISON - Winter is a good time for tree pruning, according to Wisconsin Department of Natural Resources tree health experts.
Winter pruning greatly reduces the likelihood of spreading oak wilt and other tree diseases, and minimizes pruning stress on trees.
"The best time to prune trees in Wisconsin isn't in April; it's during winter when a tree is dormant," according to Don Kissinger, DNR urban forester. "Insects and diseases that could attack an open wound on a pruned tree aren't active in winter. And without leaves, broken, cracked or hanging limbs are easier to see and prune."
Timing is especially critical when pruning oak trees. DNR foresters recommend that people stop pruning, wounding, or cutting oak trees from April through July in order to limit the spread of oak wilt. A more cautious approach limits pruning in urban areas until October 1. Oak wilt is a devastating fungal disease of oaks that has been present in the state for at least 70 years. It spreads from tree to tree by either "hitchhiking" on sap-feeding beetles that are attracted to freshly pruned or injured trees or by growing through root grafts between neighboring trees.
Red oaks, which include red, pin, and black oak, are particularly vulnerable to oak wilt. Once wilting symptoms appear, these trees die very quickly, often within a month.
Oak wilt is found commonly in the southern two-thirds of Wisconsin. In 2012, oak wilt was confirmed for the first time in Vilas, Lincoln and Sawyer counties. The disease has not been found in Ashland, Bayfield, Calumet, Door, Douglas, Forest, Iron, Kewaunee, Manitowoc, Price, Rusk, Sheboygan, Taylor and Washburn counties.
Tips to help make pruning beneficial for trees
Before pruning, consider these guidelines that will support the tree's health:
Trees should be pruned throughout their entire life, with more attention paid during the first 10 years (every other or every third year) to foster strong structural or "scaffold" limbs. Once proper structure is established, pruning can occur less often (about every five years) to maintain the structure and remove larger pieces of dead wood.
"Pruning should not take more than 25 percent of the live crown of a tree while the lower third of established trunks of deciduous trees should be free of limbs," Kissinger said.
Kissinger encourages people to review the DNR pruning brochure [PDF]. He offers these tips for tree pruning:
- Remove limbs growing toward the ground.
- Remove limbs that are crossing, rubbing, or growing parallel to one another, competing for the same space in the tree crown.
- Remove limbs growing vertically or toward the interior of the tree.
- Remove broken, cracked, diseased, or dead limbs.
- Maintain one central trunk or "leader" for as long as possible.
- Never remove so many interior branches that leaves are only present at the outside edge of the tree.
- Never prune a branch flush to the trunk as the large wound reduces the tree's natural decay barrier. The cut should begin just outside the branch bark ridge and continue at a slight outward angle.
- Never "top" trees. This makes the tree vulnerable to decay, it sucks energy from the tree, and it could lead to an early tree death.
FOR MORE INFORMATION CONTACT: Don Kissinger: 715-359-5793, Kyoko Scanlon 608-275-3275, or Brian Schwingle 715-536-0889.