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Aug 04, 2023

DNR seeks to kill invasive plants near West Okoboji Lake

West Okoboji Lake is in Dickinson County in northwest Iowa. (Photo courtesy of David Thoreson) State officials will use a herbicide to kill invasive aquatic plants that were recently discovered in two

West Okoboji Lake is in Dickinson County in northwest Iowa. (Photo courtesy of David Thoreson)

State officials will use a herbicide to kill invasive aquatic plants that were recently discovered in two canal systems that connect to West Okoboji Lake.

But the Iowa Department of Natural Resources will have to wait until next year to target another invasive species in a third area near the lake because it has already produced seed and is dying, said Jason Euchner, aquatic vegetation management biologist for the DNR.

That species, brittle naiad, is growing in the Lazy Lagoon on the north side of the lake, where it was discovered this month by the DNR’s ongoing surveillance program.

Its seeds can spread rapidly and have the potential to infiltrate the lake, which is a pinnacle feature of the Iowa Great Lakes area.

“The one thing that I want to stress about West Okoboji is that it has one of our most diverse stands of native plants anywhere in the state,” Euchner said. “They could potentially outcompete non-natives that come into the main lake. The canal areas are prone to infestation because not a lot of species occupy those areas, where the main lake itself, there’s a lot of competition going on there.”

The lagoon has a boat ramp, which is a common point of introduction of invasive plants that hitch a ride on boats and trailers from other lakes. Euchner said the nearest known infestation of brittle naiad was at Dog Creek Park — which is more than 30 miles southwest of Okoboji — but that the plant hasn’t been detected there for the past couple years.

There are brittle naiad infestations in Minnesota, but those have occurred in the Minneapolis area more than 100 miles away, according to the Minnesota Department of Natural Resources.

The plants can form dense, bushy clusters and can overtake native species.

Eurasian watermilfoil was found this month in canals near Miller’s Bay and in The Harbor. Those canals do not have boat ramps but are lined with private docks near houses.

The DNR plans to use targeted herbicide treatments to eliminate the plant, which also can form a canopy on lake surfaces that blocks other plants from growing. There are similar native species in Iowa, but Eurasian watermilfoil starts growing earlier in the year and can overtake them.

The discoveries of the plants follow an aggressive treatment that began last year of Eurasian watermilfoil in several lakes that are downstream from West Okoboji, including East Okoboji Lake, the Upper and Lower Gar Lakes, and Minnewashta Lake. That cost about $300,000 and was successful in eradicating the plant in that area.

The upcoming herbicide applications are expected to cost up to $12,000, Euchner said. Further treatment is possible.

The DNR wants people to limit their trips to and from the canals and lagoon to reduce the potential to further spread the invasive plants until it kills them. The department also wants people to remove aquatic vegetation from boats — most often their propellers — before departing from those areas to the lake.

Small bits of the plants have the ability to take root and grow in new places where they are transported.

Boat operators are required to clean plants, animals and other debris from their equipment and drain water from it when they leave lakes. They can spray boats and trailers with hot, pressurized water or let them dry for at least five days before going to a new lake.

by Jared Strong, Iowa Capital Dispatch August 16, 2023

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Senior reporter Jared Strong has written about Iowans and the important issues that affect them for more than 15 years, previously for the Carroll Times Herald and the Des Moines Register.