MICHIGAN—A collaborative United States/Canada joint project is exploring how environmental factors are affecting  the northward expansion of oak wilt, a very harmful disease impacting North American oaks.
The tree-killing disease is a serious concern along the U.S./Canadian border, according to project collaborators. Their goal is to prevent the establishment of oak wilt into the northernmost tier of the United States and into Canada.

Work being performed in Michigan is made possible in part through USDA Forest Service Eastern Region Evaluation Monitoring competitive grant funding with a 1:1 match requirement. The Forest Service provided half of the total funding amount of $112,740.

Oak wilt is currently found in 24 states, and in the Midwest the northern limit of the disease stops near the 46th parallel in Michigan, Wisconsin and Minnesota. This northern limitation of oak wilt was first observed in the 1980s, and the line has apparently not moved substantially since then.
However, climate change is expected to increasingly impact the environmental conditions of these forests in the years ahead, and the northern limitations of oak wilt are predicted to move northward over time into Canada.

Oak wilt spreads primarily through two species of sap beetles, in the family Nitidulidae. Collaborators say better understanding of the environmental factors contributing to the northern expansion risk is critical as climate change impacts become more prevalent in the coming years.
If the timing of the oak wilt-spreading sap beetle flight shifts because of climate change, then chances are the oak wilt will spread northward, too.

The collaborators are wounding northern red oaks (Quercus rubra) and setting artificial traps in Michigan’s Upper Peninsula and in Canada to attract beetles that can spread oak wilt. They are also setting up weather stations to identify temperatures and other factors which affect beetle activity in the study area.

Results of the study will help forest health managers predict the risk of oak wilt before it becomes established further north of its current range.

The idea for the project started over dinner one night. Tara Bal, assistant professor with the Michigan Technological University College of Forest Resources and Environmental Science, discussed with her counterpart Sharon Reed why oak wilt, so close to the Canadian border, had not yet moved over the line in recent decades. Reed is the forest health research scientist for the Ontario Ministry of Natural Resources and Forestry in Canada and has been studying oak wilt since 2017.

Bal said, “We have oak trees with all the beetles (in Michigan), but the disease has not yet affected northern oaks in Canada, New York and elsewhere.”

The collaborators are now conducting beetle identification training, leading joint presentations, and will be working together on future research papers.

Bal added they hope to be better able to predict the risks and where and when oak wilt might be moving north, plus refine prevention guidelines that are based on beetle flight data collected in other places in the Midwest. “This could reduce the burden on industry and become more scientifically appropriate.”

Work being performed in Canada is being paid for by the Canadian Food Inspection Agency and the Manitoba Ministry of Natural Resources and Northern. The Michigan Invasive Species Grant Program is contributing additional funds to support a graduate student at Michigan Technological University. The remainder is in kind funding from different organizations.

Natural Resources Canada, the City of Ottawa, York Conservation Authority, the Manitoba Ministry of Natural Resources and Northern Development, and Michigan Department of Natural Resources are also involved in the project.

About 20 people in all are directly involved in the project which will wrap up in late spring 2024.