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.
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:
FOR MORE INFORMATION CONTACT: Don Kissinger: 715-359-5793, Kyoko Scanlon 608-275-3275, or Brian Schwingle 715-536-0889.