FARGO, N.D. — We got some pretty big news in early March. Emerald ash borer (EAB) was found in Moorhead, Minnesota, by the city’s forestry crew.
EAB is a non-native insect that’s been in North America for more than 20 years, killing ash trees. It was discovered in the United States near Detroit, Michigan, and has been slowly spreading towards North Dakota.
On the one hand, the find in Moorhead wasn’t much of a surprise. We’ve known for a long time that EAB would eventually make its way to our area. Previously, the closest infestation in Minnesota was Sauk Centre, about 130 miles southeast of Fargo.
EAB was discovered in Sauk Centre in 2019.
And then, it didn’t come any closer in 2020, 2021 or 2022. The recent find is a big jump. The insect likely arrived via human means.
What does the Moorhead discovery mean for North Dakota?
That’s such a broad question that it’s difficult to give an easy, direct answer. If you don’t have ash trees in your yard or shelterbelt, then there’s no risk to your trees. And there’s a big difference, at least in the short run, depending on where you live. I’m pretty sure we won’t find EAB for a while in, say, rural McIntosh County. A find in Fargo is much more likely.
If you suspect that your ash tree is infested with EAB, you can report it to the North Dakota Department of Agriculture via their website at http://www.ndda.nd.gov/eab or via email at email@example.com.
In the short run, folks in the Fargo-Moorhead metro area must think about making some decisions.
Do you want to keep your ash trees for the future, or is it time to remove and replace them? It’s not an easy choice.
City foresters throughout the region have been working for years to reduce the percent of ash trees in the urban forest. It’s a difficult task, as green ash was the most-planted tree species for a long time.
I can understand why.
Green ash grows quickly and is adapted to a variety of sites across the state – sandy soils, wet sites, and even salty areas have green ash growing in them. Green ash often can tolerate the compacted soils found in urban areas. It’s an amazing tree.
And the risk to that species just went up.
Looking at costs and benefits can help with your decision making. For trees that have poor structure or are in declining health, it’s pretty easy to justify removal and replacement. That’s actually been the main approach of those city foresters working towards diversification. Remove the trees that don’t provide much benefits – perhaps those that are still small or are located under power lines – but keep the ones that are in good health and are structurally sound.
Even though there’s a cost to removing trees and planting new ones, there are benefits as well, and the risk of loss is substantially decreased.
Retaining those larger, healthier ash trees also comes at a cost. There are several effective chemical treatments available for controlling EAB. While many of these are available to homeowners, the treatments that professionals offer are usually more effective, as the professional-grade chemicals are at higher concentrations than those available for homeowner use.
The chemical insecticides used to control EAB must be reapplied every 1 to 2 years, depending on which one is being used. That annual cost has to be factored into your decision making. In any given area, EAB is likely to take at least 10 years to work its way through the local population of ash trees. Do you want to continue to treat your ash tree – or trees – for that long?
Decisions. And they’re not easy ones.
My wife and I have to decide what to do with our own ash trees. I’m pretty sure we’ll take out the one that’s closest to the house. It lost a major branch about five years ago, and I’ve already planted its replacement underneath the current crown. That young tree is now four years old and is establishing well.
Will we treat the other ash tree and keep it? Or should we take it out?
Only time will tell.
— Joe Zeleznik, NDSU Extension