Emerald ash borer tunneling

Winding S-shaped patterns under the bark of an ash tree are a telltale sign of an emerald ash borer infestation. The invasive insect was confirmed in Lyon County this month.

INWOOD—Eleven years after emerald ash borer was confirmed in Iowa, the invasive insect has found its way to Lyon County.

Ash trees infested with emerald ash borer were discovered at the Big Sioux River Complex Wildlife Management Area west of Inwood near the state border last week.

The invasive insect also was discovered in Fremont and Wright counties for the first time, bringing the total of Iowa counties with confirmed cases up to 80.

This is the first time the shiny, green insect has been found in N’West Iowa, but in 2018 it was confirmed in Sioux Falls, SD, and in 2019 the beetle was found in Worthington, MN.

Lyon County Conservation director Craig Van Otterloo said its spread to N’West Iowa was inevitable.

“It was a matter of time, that’s what I feel,” Van Otterloo said. “Sioux Falls has it, Worthington has it, Storm Lake has it. So guess what, it’s coming. We’re surrounded.”

The invasive species is able to kill an ash tree in two to four years.

Adult emerald ash borers are about half an inch long and feed on the leaves of ash trees. The larvae are responsible for the devastating damage to trees.

Females lay eggs in the bark of ash trees and when the eggs hatch, the larvae gnaw through the bark to the growing layers of the tree. As they chew their way through the wood, they leave winding S-shaped tunnels.

Those tunnels, or galleries, are one of the telltale signs of an infestation.

Other signs include branches dying from the top down. Bark riddled with woodpecker holes is another giveaway. The birds can quickly strip away bark to get at larvae.

Confirmation of emerald ash borer may lag a year or two behind when an infestation is spotted and confirmed, which means the insect may have spread farther than Lyon County.

“The difficulty with emerald ash borer is when it first shows up in the area, the signs and symptoms really aren’t noticeable,” said Mike Kintner, the emerald ash borer coordinator for the Iowa Department of Agriculture and Land Stewardship.

He spotted the affected Lyon County trees while driving by the area.

“It’s likely that it’s in other places,” Kintner said. “We just haven’t turned it up yet or confirmed it in those areas.”

On its own, emerald ash borer travel one to two miles per year from one infested tree to the next. The primary way it spreads is through human assisted means when infested wood is transported to new locations.

Iowa is under a federal firewood transport quarantine. Transporting firewood within the state or into other quarantined states is not illegal but is strongly discouraged. Instead, people are encouraged to “burn it where you buy it” and obtain firewood in the county where it will be burned.

Van Otterloo said this rule was not strictly enforced in Lyon County previously. Although transporting firewood out of the county runs the risk of spreading to uncontaminated counties nearby, he said it’s not likely to be long before the borer is found at Lake Pahoja.

Lake Pahoja is about seven miles as the crow flies from the known site near Inwood. The Iowa Department of Natural Resources considers anywhere within 15 miles of a known infestation to be at risk of emerald ash borer.

“We’re in the radius already,” Van Otterloo said. “It’s going to get here sooner or later, we’re not going to withstand this by doing that.”

There are a few ways to chemically treat ash trees for emerald ash borer, but these are expensive and results are not guaranteed.

Sarah Rueger, a district forester with the Iowa DNR said these treatments will, at best, delay infestation and do not prevent the insect from taking hold.

“It’s one of those things where the host won’t stop until the source of food is gone. The ash borer is going to blast through until the ash is pretty much gone,” she said.

Another option is to preemptively remove ash trees and replant with other species, but Rueger said the effectiveness of this in preventing the borer’s spread is uncertain and should be treated on a case-by-case basis.

Conservation staff have been preparing for emerald ash borer for several years. There’s a nursery of more than 1,000 young trees of different species that will be planted to replace ash killed by the borer.

“We have not planted ash trees out here for 10 years at Lake Pahoja,” Van Otterloo. “We’ve kind of planned for it. The ash borer is going to get here. As they die we are going to plant replacements.”

He compared emerald ash borer to Dutch elm disease, which wiped out 75 percent of the species in the country 40 years ago.

A fungus spread by elm bark beetles causes Dutch elm disease. An elm tree will try to protect itself from the fungus by plugging its xylem tissue, the water-conducting cells that transport food and water. Plugging that tissue causes the tree to die.

Although there are Dutch elms that have survived, including in Lyon County, most were replaced with ash trees, which is part of why the emerald ash borer poses such a threat to wooded areas in N’West Iowa and around the country.

Van Otterloo advises private landowners thinking about how to replace ash killed by the borer to plant multiple species to avoid seeing entire groves wiped out by diseases or parasites.

“Guess what was planted when all the Dutch elm disease came through? Green ash, and we have a plethora of green ash out there and now we have to deal with this,” Van Otterloo said. “Plant multiple species so if something comes through you’re not decimated.”