Contact(s): Paul Cigan, DNR forest health specialist, Paul.Cigan@wisconsin.gov, 715-416-4920 or Don Kissinger, DNR urban forestry specialist, Don.Kissinger@wisconsin.gov, 715-348-5746
December 11, 2018
MADISON -- It may not sound like fun, but winter in Wisconsin is an excellent time to prune oak trees. Pruning in winter offers all the benefits of pruning while minimizing the spread of tree diseases. One such disease is oak wilt, a fatal tree disease that spreads through tiny sap-feeding beetles attracted to open wounds on trees.
"Dormant trees in winter are easier to prune because damage is much more visible on tree branches after their leaves have fallen, and pruning is more effective because harmful pests are inactive in cold temperatures," said Paul Cigan, forest health specialist in northwestern for the Wisconsin Department of Natural Resources.
Trees should be pruned throughout their entire life to maintain strong structure and remove dead wood. Young trees should be pruned to establish a central trunk, proper trunk taper, and good branch structure and spacing. Older trees should be pruned to remove dead and/or hazardous limbs. But pruning oaks during warmer months of April through July places them at greatest risk for oak wilt infection and should be avoided where possible.
While oak wilt often spreads locally through tree injury, it can also move greater distances on or in firewood logs. Taking recommended precautions, such as pruning in winter, and keeping firewood local will help protect trees in your area and prevent the spread of oak wilt to new counties and townships.
"Several recent oak wilt finds in northern Wisconsin, including first finds in Bayfield and Douglas counties and in over a dozen new northern townships, may have been the result of infected firewood brought from areas with oak wilt," Cigan said.
Experts recommend keeping oak firewood at the same location where it is cut for one year, or until the bark is naturally loose, to prevent the spread of oak wilt.
The DNR offers a pruning brochure with more detailed, step-by-step tips for tree pruning. Find it by searching the DNR website, dnr.wi.gov, for keywords "tree pruning." Certified arborists who offer pruning and other tree care services can be found at waa-isa.org/arborists/search.asp (exit DNR). For additional information about oak wilt, search the DNR website, dnr.wi.gov, for keywords "oak wilt."