Greater Michigan Timber Management

  Avoid Unnecessary Tree Pruning, Cutting

Oak wilt is a serious disease of oak trees - mainly red oaks, including northern red oak, black oak and pin oak - in Michigan and seven other neighboring Midwestern states. Red oaks will die within a few weeks after becoming infected, though white oaks are more resistant and the disease progresses more slowly. The spring of 2012 saw the disease risk for trees  especially high and ahead of schedule.

"The most preventive measure to prevent oak wilt is by not pruning, trimming, or otherwise 'injuring' oaks from April 15 to July 15. The spread of oak wilt occurs during this time of year as beetles move spores from fungal fruiting structures on last year's oak wilt-killed trees to wounds on healthy oaks. Because of the warmer weather this spring, the risk is higher and the beetles that move oak wilt - and the oak wilt inoculum - are present in many areas.

 According to the Michigan DNR, oak wilt has not been detected in every Michigan county, however, the need for vigilance is present statewide. "With the transport of firewood and other tree-related activities, you have to assume the risk is present.

Oak wilt has already been detected in the following counties: Alcona; Allegan; Alpena; Antrim; Barry; Benzie; Berrien; Calhoun; Cass; Cheboygan; Clinton; Crawford; Dickinson; Genesee; Gladwin; Grand Traverse; Iron; Kalamazoo; Kalkaska; Kent; Lenawee; Livingston; Macomb; Manistee; Menominee; Midland; Missaukee; Monroe; Montcalm; Montmorency; Muskegon; Newaygo; Oakland; Ogemaw; Oscoda; Ottawa; Roscommon; Saginaw; Shiawassee; St. Joseph; Van Buren; Washtenaw; Wayne; and Wexford.

Springtime is a popular time for people to move firewood to vacation properties and other locations. During this April-to-June period, it is advised not to move wood from oak wilt-killed trees. These trees are often cut into firewood and moved, sometimes many miles from their original locations. Any wounding of oaks in this new area can result in new oak wilt infections as beetles move spores from the diseased firewood to fresh wounds on otherwise healthy trees.

It is recommended that anyone who suspects they have oak wilt-tainted firewood should cover it with a plastic tarp all the way to the ground, leaving no openings. This keeps the beetles away and generates heat inside the tarp, helping to destroy the fungus. Once the bark loosens on the firewood, the disease can no longer be spread.

New oak wilt sites have been traced to spring and early summer wounding from tree-climbing spikes, rights-of-way pruning, nailing signs on trees, and accidental tree-barking. If an oak is wounded during this critical time cover the wound immediately with either a tree-wound paint or a latex paint, this will help keep the beetles away.

Once an oak is infected, the fungus moves to neighboring red oaks through root grafts. Oaks within approximately 100 feet of each other - depending on the size of the trees - have connected or grafted root systems. Left untreated, oak wilt will continue to move from tree to tree, progressively killing more red oak over an increasingly larger area. These untreated pockets also serve as a source of inoculum for the overland spread of the disease.