Monday, February 2, 2015

Prune trees in winter instead of spring to help prevent oak wilt

Now is a good time for tree pruning, while temperatures remain cold, according
Oak wilt infected oak leaf. DNR photo
to Wisconsin Department of Natural Resources tree health experts.
"The best time to prune trees in Wisconsin is during winter when a tree is dormant," said DNR Urban Forester Don Kissinger. This is because:
  • Insects and diseases that attack open wounds on pruned trees aren't active in winter, and
  • Without leaves on the trees it is easier to see and prune broken, cracked or hanging limbs.
"Timing is especially critical when pruning oak trees," said Kyoko Scanlon, DNR Forest Pathologist. DNR recommends no pruning, wounding, or cutting oak trees from April through July (through October to be extra cautious) to limit the spread of oak wilt, a fatal disease of oaks. Your municipality may have their own oak wilt ordinances that you should follow as well.
To help reduce the spread of oak wilt another way, do not move firewood. "Several recent oak wilt finds in northern Wisconsin were probably the result of infected firewood brought from areas with oak wilt," according to Paul Cigan, DNR Northwest District Forest Health Specialist.
  • Keep oak firewood where it is cut for one year, or until the bark is naturally loose, to prevent the spread of oak wilt.
Oak wilt is still uncommon in much of northern Wisconsin. Taking precautions to prevent the spread of oak wilt will help keep it that way.
For additional information online, search the DNR website,, for keywords "oak wilt".

Pruning tips

Trees should be pruned throughout their entire life to maintain strong structure and remove dead wood. "Pruning should not remove more than 25 percent of the live crown of a tree. The lower third of trunks of deciduous trees should be free of limbs," Kissinger said. The DNR pruning brochure offers more detailed, step by step tips for tree pruning. Find it by searching the DNR website for "tree pruning [PDF]".