Sioux City Anticipates Arrival Of Invasive, Tree-Killing Beetle

Jun 18, 2019

An invasive beetle is expected to move west in Iowa, prompting one city to look into how to deal with it.

Sioux City council members on Monday heard a presentation from the city parks and recreation department about the invasive emerald ash borer – an insect known for killing millions of ash trees across the country. Sioux City Parks Maintenance Field Supervisor Kelly Bach said tree mortality rises within a few years of an infestation.

“That’s if you do absolutely nothing at that point and just leave it be,” Bach said.

The city is looking at several ways to manage the emerald ash borer: It could simply remove trees once they die, remove all ash trees before the insect arrives and replace them with another species, treat the trees with chemicals that will kill the insect, or combine all three approaches together. Ash trees make up more than a quarter of Sioux City’s trees.

Bach’s staff is recommending the city implement the combined approach. Treatment would have to be done every two to three years, he said.

The destructive beetle’s larvae snack on tissue under tree bark, cutting off nutrients and water from moving through, ultimately killing trees. The insect has so far been spotted in two-thirds of Iowa’s 99 counties, mostly in the east and south. Other than Buena Vista County, 19 counties in northwest Iowa are likely untouched.  

A map from the U.S. Department of Agriculture, Iowa Department of Ag., Iowa DNR and Iowa State University also shows where the emerald ash borer has been detected and the recommended treatment areas, which includes a 15 mile buffer of where to treat.

State environmental officials are expecting it to creep further west over time, following where people transport firewood and even latching onto railway systems, said Emma Hanigan, the urban and community forestry coordinator for the Iowa Department of Natural Resources.

“On railways, emerald ash borer can just attach, and, instead of flying, be carried across the state that way,” Hanigan said.

Hanigan noted U.S. Highway 34 and a nearby railroad system in southern Iowa have been hotspots for the spread.

The reason they’re expecting it to move west in Iowa, Hanigan said, is because that has been the pattern across the U.S. The emerald ash borer was first discovered in Michigan in 2002 and has “spread outward from there” she said.

According to a map of emerald ash borer sightings from Iowa Department of Agriculture’s Entomology and Plant Science Bureau, the beetle first surfaced in Iowa in 2010. From 2010 to 2017, it primarily hit southern, central and eastern Iowa. 

A map showing where the emerald ash borer has been confirmed.
Credit Credit Iowa Department of Agriculture & Land Stewardship, Entomology & Plant Science Bureau

In 2018, the beetle reached Carroll, Crawford and Pottawattamie counties in western Iowa. It was confirmed in Cass County in February, the only new detection in the state this year. It has also reached Alta in Buena Vista County and was found in 2018 in Sioux Falls, South Dakota, 90 miles to the northwest of Sioux City.

“It is within 90 miles of Sioux City, both to the east and to the northwest, so we need to have this in place so that we have a plan rather than, ‘it’s here, now what do we do?’” Bach said.

Sioux City Mayor Pro-Tem Dan Moore said the city will need to educate people about the insect. The city is planning to hire a dedicated staff member.

“We’ve built that into our budget to add someone, to take on the issues that will be coming up that we predicted, and [Bach's] predicted, that will happen and occur in the next three years,” Moore said.

The symptoms of emerald ash borer are often not seen until a couple of years after an initial infestation, Hanigan said. She said communities in western Iowa should anticipate that it will come and “start planning for their ash.”

“Without symptoms, we’re unsure of the spread. We continue to monitor,” Hanigan said. “But for western Iowa communities, it could be that they may have emerald ash borer found this year. It could be another seven years. We just don’t know how that spread will look across northwest Iowa.”