Invasive, tree-killing emerald ash borer confirmed in Fargo

The invasive emerald ash borer, a type of beetle that bores into and eventually kills Ash trees, has been discovered in Fargo for the first time, raising concerns that insects could devastate trees and wooded areas here as it has in other parts of the country. 

The invasive species, originally from Asia, is believed to have come to North America in wooden pallets and other imports. It was first discovered in North America in southeast Michigan in 2002, and according to the U.S. Department of Agriculture, it has now spread to 37 states, including Minnesota and North Dakota, killing tens of millions of Ash trees across the country.

The discovery of the emerald ash borer is not a surprise to Fargo city officials, considering the bug has plagued the neighboring city of Moorhead since 2023. The emerald green colored beetle, with a reddish or copper-colored abdomen, lays its eggs in the crevices of Ash tree bark, according to the USDA. After hatching, the larvae feed on the inner bark and the tree’s nutrients, creating S-shaped markings. The larvae then burrow deeper inside the tree during winter to pupate, and adults emerge again in spring.

Scott Liudahl, a forester with the City of Fargo, says the recent news is “not gloom and doom right at this point.”

The Fargo forestry department has been preparing for the eventual discovery of emerald ash borer by diversifying their urban forest system, by growing other types of trees other than Ash. 

16 years ago, around 40 percent of the trees within Fargo were Ash trees.

Now, only 21 percent of Fargo’s 62,000 or so trees are Ash.

Liudahl says “We know that having too much of one thing is not good, especially when it comes to tree species.”

Now that emerald ash borers are in Fargo, he says there are a couple ways to help slow the spread. One is simply by avoiding the movement of firewood. He advises residents to not bring firewood in from outside the city and to not move it outside the area, either.

“Get it locally. (Moving ash wood is) the number one way that pest(s) (are) going to be moving around Fargo, and out of Fargo as well,” Liudahl says.

Another way to prevent an infestation of these green insects is by injecting an insecticide into the base of healthy trees. The city plans to pay a contractor to inject trees starting in June, when Ash trees will be blooming. This means the insecticide will circulate faster.

“That provides two years, even in some cases we are talking three years of protection. Treating a high value tree can be a lot less costly than removing and replacement,” says Liudahl.

Liudahl says if residents have ash trees they want to protect on their property, prices will range from around $10-$15 per inch of diameter. That means treating a mature Ash tree that is 18 inches in diameter might cost around $180 - $270.

The recent frigid temperatures in the area around Fargo (and across the upper Midwest) may help slow the spread of emerald ash borers. Temperatures must be incredibly cold to have an effect on the bugs, which are insulated by the tree and produce their own antifreeze, which allows their body to dip below freezing without dying, according to the Minnesota DNR.

The University of Minnesota Extension says research shows that about 50 percent of larvae will die when air temperatures reach 20 degrees below zero, and 90 percent or more of the larvae will be killed when temps plummet to 30 degrees below zero or colder.

“Being in a cold environment, this is a good thing. It's a kind of a management strategy,” says Liudahl.

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