Preventing Oak Wilt in Grand Rapids

A New Threat to Grand Rapids’ Trees

City advises caution to prevent spread of oak wilt

GRAND RAPIDS, Mich. – For most people, April 15 is the annual tax-filing deadline. For people like City Forester Dan Coy – and other forest health professionals – April 15 also marks the beginning of the yearly window when oak wilt can be transmitted from diseased to healthy red oak trees.

What We Can Do

  • Don’t move firewood!
  • Don’t prune oaks and elms between April 1 and July 31. (Fresh pruning cuts during the spring and early summer strongly attract disease-carrying insects.)
  • If possible, the pruning of oaks and elms should wait until after November 1st when there is no risk of attracting disease-carrying insects. There is a lesser risk between August 1st and November 1st.
  • If trees must be pruned or are accidentally damaged at any time during the growing season (April – November), treat wounds immediately with a latex based tree wound dressing.
  • If you suspect a tree is infected, consult a qualified Arborist.
  • Buy young trees only from reputable nurseries that respect quarantines.
  • Plant a wide diversity of tree species.
  • Learn to identify tree-threatening insects and evidence of disease such as dieback and exit holes. In most cases, early detection of insect and disease issues have been discovered by citizens just like you!

What The City Is Doing

The City of Grand Rapids is doing its part to address these challenges. The city is:

  • Addressing oak wilt in public oak trees by identifying and removing infested trees to prevent spread and treating uninfected adjacent trees
  • Pruning oaks only during the dormant season.
  • Planting a wide diversity of tree species to minimize vulnerability to new exotic diseases.


More About Oak Wilt

According to Coy, a certified arborist with the City’s parks and recreation department, oak wilt is a serious disease of oak trees. It 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 normal time-tested advice is to prevent oak wilt by not pruning or otherwise ‘injuring’ oaks from April 15 to July 15,” Coy said.

He added that 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. As warmer weather melts away snow and ice, the beetles that move oak wilt become active.

Unfortunately, many people learn not to prune or otherwise wound trees from mid-April to mid-July only after they lose their oaks to oak wilt, he said.

Oak wilt disease is the latest threat to large scale tree mortality in the United States due to the introduction of invasive, exotic species. In the early 1900s, approximately four billion American chestnut trees died in the United States from chestnut blight. Between 1930 and 1990, more than 75 percent of North America’s 77 million elms died from Dutch elm disease. Most of the 8.7 billion ash trees throughout North America will die from the emerald ash borer. In the Grand Rapids metro area, tens of thousands of ash trees have been lost.

As the global economy has expanded, so has the rate of introduced species. Because these exotic insects and diseases are not native to the U.S., there are no natural predators to keep them in check.

Coy says new exotic pests loom on the immediate horizon and threaten our trees. Oak wilt disease, beech bark disease and the hemlock wooly adelgid endanger the oak, beech and hemlock trees, respectively. In West Michigan, oak wilt disease, the most serious of the new exotic threats, is on the verge of becoming the next emerald ash borer. Several outbreaks of oak wilt have occurred within Grand Rapids and the surrounding communities. If left unchecked, these have the potential to cause great harm.

Spring is a popular time for people to move firewood to vacation properties and other locations. During this April-to-July period, Coy said 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 Michigan Department of Natural Resources (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.

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 (a wound created when bark is removed via impact from equipment, falling trees and other causes). If an oak is wounded during this critical time, the DNR advises residents to cover the wound immediately with either a tree-wound paint or a latex paint to help keep 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.

As more trees die from oak wilt, more spores are produced which contribute to the overland spread of oak wilt.

Steps can be taken to protect trees and slow down oak wilt’s spread. With the experience gained from dealing with the emerald ash borer crisis, we know that taking these steps makes a difference.



To learn more about how to take care of your trees, check out resources from the Urban Forest Project and consider becoming a Citizen Forester!

For more information about oak wilt in Michigan, go to

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