Emerald Ash Borer (EAB), an invasive insect, has impacted ash trees in Minnesota since 2009, when it was first discovered in St. Paul, and has been confirmed in 56 counties across the state. EAB larvae kill ash trees by tunneling under the bark and feeding on the tissues that transport nutrients. Infested trees often show signs such as increased woodpecker activity due to the birds feeding on the larvae, and characteristic S-shaped galleries may be visible under splitting bark.

 Photo: "S" shaped galleries. MDA

While not yet confirmed in Cook County, its presence in neighboring Lake County, Minnesota, and Thunder Bay, Canada, has raised concerns among Cook County community members, government officials, and natural resource professionals.

Lake County

EAB was first confirmed in Lake County, Minnesota, in April 2022. This initial infestation was discovered by a staff member of the Superior Hiking Trail Association, who observed woodpecker damage on an ash tree along a hiking trail in Two Harbors and reported it to the Minnesota Department of Agriculture (MDA). An original quarantine was put in place, which restricts the movement of wood and ash materials from the area to help reduce the spread of EAB. 

In 2024, a Minnesota Department of Natural Resources forester identified unhealthy ash trees in the city of Silver Bay, leading to additional EAB confirmations. The original quarantine area was expanded to include townships in the southern half of the county. 

 Image: MDA

Thunder Bay

Across the Canadian border, EAB was detected in Thunder Bay in 2016 and has since spread throughout the city. Nearly one in five trees in Thunder Bay are ash, causing the city to implement a management plan to protect some ash trees, remove others, and replant with different tree species to increase diversity and forest health. A ban is also in place against transporting firewood outside city limits.

Cook County EAB-Related Events

Multiple events are scheduled in June to raise awareness and educate community members on EAB prevention. The Cook County UMN Extension is hosting an EAB Early Detection workshop on Friday, June 20, 2025, from 1:00 PM to 2:30 PM at the Cook County Community Center. Presenters from the MDA will share information on identifying, reporting, and managing EAB. 

This free workshop is open to all interested individuals, with pre-registration requested at z.umn.edu/EAB-CookCounty.

Additionally, the Cook County Invasives Team, a collaborative group of agencies and organizations focused on managing invasive species, will host an educational event at Voyageur Brewing in Grand Marais on Saturday, June 21, 2025, from 2:00 PM to 4:00 PM. This family-friendly event will allow community members and visitors to learn about various invasive species affecting Cook County, participate in activities and games, and purchase a limited-release "Emerald Ash Beer" Blonde Ale. All are welcome to attend.