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Emerald ash borer threatens northern Minnesota

With close to a billion ash trees in the state, the non-native emerald ash borer (EAB) insect threatens trees across Minnesota, but especially the northern part of the state.

A wood borer that feeds in the phloem and disrupts the movement of nutrients, EAB infestation results in eventual mortality of a tree.

The first discovery of EAB in Minnesota was in 2009 in St. Paul. It has now spread to 45 counties throughout Minnesota, including Duluth in St. Louis County in late 2015 and Carlton County in April 2022. Recently, EAB was found in Cass County. This find is significant because it is an isolated find in Minnesota’s forested region, particularly in forests where one of the dominant species is black ash.

Minnesota has close to one billion ash trees with black ash representing 80 percent of the ash species, putting it near 800 million trees in the state. The majority of the black ash forests are located in northern Minnesota. Most of these forests are characterized as wetland forests, with black ash composing more than 75 percent of the canopy and understory components. Thus, EAB moving into northern Minnesota in these black ash-dominated wetland forests is a serious concern about the impact it will have on these ecosystems.

The main concern is that EAB will kill most of the black ash in these forests, changing the ecosystem in the process. These sites could change and be composed of grasses, cattails, and shrubs. This would then impact the plants and animals that rely on the black ash ecosystem. However, it will still be some time until EAB makes a very noticeable impact on northern black ash forests. This provides time to prepare for the future mortality of ash trees.

One main tactic is to start diversifying black ash forests by planting trees not susceptible to EAB attack. Research has started to examine species that will thrive in these ecosystems, with the main goal of keeping these sites forested. The movement of EAB throughout northern Minnesota is most likely inevitable, but there is time to prepare and, hopefully, the state can maintain the forested regions in Minnesota.

Property owners who suspect a tree has been infested with EAB should call the MDA office at 888-545-6684. There is also a reporting portal on the MDA website, http://www.mda.state.mn.us/eab.

Here are a few more notes on the EAB:

• Woodpecker activity is a top sign of tree infestation, as well as the S-shaped feeding marks left under the bark of a tree.

• Damage to a tree will be found mid-trunk and higher.

• It can take about five years for a tree to die after being infested. EAB is spreading about 1 or 2 miles a year.

• Injections of insect repellant are recommended for larger trees. Ground-soaking with chemicals can work with smaller trees. Professionals are required for tree injections, while soaking materials can be purchased by property owners. Injection treatments cost $7 to $10 per diameter-inch of the tree. Treatments last for about two years.

Find additional information on emerald ash borer at https://www.mda.state.mn.us/eab and https://www.dnr.state.mn.us/invasives/terrestrialanimals/eab/index.html.