DNR Asks Residents to Help Prevent Spread of Oak Wilt Disease

The DNR is reminding residents they can help prevent the spread of oak wilt disease this spring.

April 15 marked the beginning of the yearly window when oak wilt can be transmitted from diseased to healthy red oak trees.

Oak wilt is a serious disease of oak trees that mainly affects red oaks, including northern red oak, black oak and pin oak. Red oaks often die within a few weeks after becoming infected. White oaks are more resistant; therefore, the disease progresses more slowly.

The spread of oak wilt occurs during this time of year as beetles move spores from fungal fruiting structures on the trees killed last year by oak wilt to wounds on healthy oaks.

The normal time-tested advice is to prevent oak wilt by not pruning or otherwise ‘injuring’ oaks from April 15 to July 15.

oak+wilt++2016Many people learn not to prune trees from mid-April to mid-July only after they lose their oaks to oak wilt.

Although oak wilt hasn’t been detected in every Michigan county, Mech said the need for vigilance is present statewide.

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

The DNR recommends 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.

Oak_wilt_aerial_photoOnce 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.

As more trees die from oak wilt, more spores are produced, and that contributes to the overland spread of oak wilt.

To minimize the risk of oak wilt infection caused by logging damage, the DNR limits the cutting of red oak trees on state-managed land between April 15 and July 15. This helps protect red oak trees left after thinning from damage that could lead to infection.

The DNR recommends private forest landowners exercise caution during this period and, whenever possible, delay harvesting activity in oak forests until after July 15 to reduce the risk of oak wilt.

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