Arrival of emerald ash borer has Kandiyohi County, Minnesota Department of Agriculture on alert

·5 min read


— The announcement from the Minnesota Department of Agriculture in late May that the

emerald ash borer had officially been found in Kandiyohi County

was an unwelcome, but not unexpected, surprise. The issue now is what can be done to slow the spread and mitigate the damage already being done.

"It is very concerning," said County Administrator Larry Kleindl, at Tuesday's Kandiyohi County Board meeting. "Most of our county parks, most of our public lands have ash trees."

In a virtual public information meeting for Kandiyohi County residents on Wednesday, Jonathan Osthus, Minnesota Department of Agriculture technical assistance coordinator for emerald ash borer, explained what might happen over the next several years. All true ash trees, including black, green and white, are at risk. A recording of the meeting can be found on the

Minnesota Department of Agriculture website


"They are a very common tree in the landscape," Osthus said. "All three that are native to Minnesota are highly susceptible to the emerald ash borer."

While emerald ash borer is officially identified in only three trees around Nest Lake, Osthus said residents should understand that if they are within the generally infested area

mapped out by the department

, then their ash trees are probably infested as well and property owners need to start thinking about next steps.

"All those ash trees on those streets, in those neighborhoods, all show some level of symptoms of emerald ash borer," Osthus said.

The emerald ash borer kills a tree by its larvae tunneling through the tree, breaking the connections between the roots and the canopy needed to transfer nutrients through the tree. The sure way of identifying an infestation is to look under the bark. The larvae leave very distinct S-shaped galleries as they bore and feed within the tree.

"It is the easiest and most common way to identify it," Osthus said.

While one or two emerald ash borer probably wouldn't kill a healthy ash tree, a fully mature female can lay 60 to 90 eggs, causing the larvae population to explode within just a few years of first infecting the tree. It is then the tree really begins to suffer.

"You have thousands of beetles infesting a single tree," Osthus said. "Once that population builds up, you have a lot of trees die in a short amount of time."

It can take several years before a tree dies from the pest invasion, depending on the health of the tree. On average, the first year there are practically no visible signs of an infestation, Osthus said.

In year two, there is the possibility of viewing woodpecker damage. Emerald ash borer larvae are a very tasty meal for woodpeckers, so if there are a number of shallow, oval-shaped, dime-sized and light-colored woodpecker holes across an ash tree, that could be sign of an infestation.

In year three, woodpecker damage is likely as is bark splitting as the tree tries to heal from the damage of the pest. By year four, there will be noticeable thinning of the tree's canopy. By years five and six, the tree is either dying or dead.

If property owners find that their ash trees are infected by emerald ash borer, or are located in or near an infected area, there are really only two options open to them.

First, there are insecticides that can be used to treat ash trees, either before the pest arrives or within the first few years of an infestation. Those treatments usually have to be repeated every couple of years and. depending on the size of the tree, will have to be done professionally.

Insecticides that are available for purchase by the public are usually effective only for trees less than 15 inches in diameter and the insecticides can have negative impacts on pollinators. If the treatments are done correctly and early enough, they can either keep a tree from being infected or kill off a small invasion of the pest.

"It all depends on the situation," Osthus said.

The only other option is to remove ash trees, either before or after emerald ash borer arrives. Ash trees dry out quickly after death, making them dangerous to leave standing.

Osthus recommends people have the infected ash trees removed before they are completely dead. It is best to wait until fall and winter to do any such work, as any emerald ash borer in the tree would be dormant and there would be a smaller risk of spreading.

Whether to begin removing ash trees or try to treat trees before the damage is irreversible is now a question facing cities and counties where the emerald ash borer has been found. There are 35 counties in Minnesota with infestations. Ash have been very popular trees to use along boulevards and within parks, especially after Dutch elm disease caused widespread tree death in elms.

On average, emerald ash borer spreads naturally about two to three miles a year by adult beetles flying from tree to tree. However, human-caused movement, usually by transporting infected firewood, has helped the pest spread farther and more quickly.

This is why the northeast quadrant of Kandiyohi County is now under an emergency quarantine, joining other impacted areas. This means no part of the ash tree and no hardwood firewood from any species may leave the quarantined area. Firewood from Canada or other states are also not allowed into Minnesota.

"Pests can definitely be hiding in that firewood," said Danielle DeVito, Minnesota Department of Agriculture regulatory coordinator.

The best option for people looking forward to a summer campfire is to either purchase or find the firewood where it will be burned or buy Minnesota Department of Agriculture-certified firewood that has been treated for pests and can safely be moved around the state.

People should report suspected infestations to the Department of Agriculture. The more descriptive the report the better, and photos are always helpful.

"I would ask the citizens of Kandiyohi County to keep their eyes open," Kleindl said on Tuesday. "Be active in monitoring your ash and we will do the same in our county properties. This is one of the things we did not want to happen in our county."