Recent shot of winter doesn't put unwanted weed on ice

Thursday, April 19, 2018
DNR fisheries biologist Mike Hawkins held a sample of what he called juvenile curlyleaf pondweed after casting a vegetation rake into East Lake Okoboji. He said the budding plants are more compact in the early phases, but are present in the lake. He joked the weed is one of the few green plants at this point in the year.
Photos by Seth Boyes

SPIRIT LAKE Mother Nature isn't the ally Lakes residents are hoping for in their ongoing battles with the curlyleaf pond weed.

DNR fisheries biologist Mike Hawkins said the amount of growth for 2018 was set last fall when the curlyleaf pondweed germinated. A delayed arrival of ice in the Iowa Great Lakes and the low amount of snow cover at the start of the season also helped the weed establish itself for the upcoming spring and summer.

"A couple of weeks ago, we actually drilled a number of holes on East Okoboji and took a look at what kind of growth was underneath the ice," Hawkins said. "I hate to make big predictions from a few holes popped in the ice but: Everywhere we looked, we had good growth of curlyleaf pondweed under the ice. The indications that I have are that (the snow cover is) probably not going to affect it. The plant looked very healthy."

Curlyleaf pondweed is a plant that can tolerate conditions of low light. Shade caused by snow cover over the Lakes may have only slowed down the growth near the end of the winter season.

"We don't have a lot of data on this, but it did seem like the growth cycle of the plant started very, very early last fall," Hawkins said. "So, given that, we may see an accelerated growth period after ice out."

The accelerated growth could result in the plant's early demise as summer conditions arrive in the Iowa Great Lakes.

"It's a cool-water plant and as water temperatures come up fairly rapidly in June that's what really ends its life cycle," Hawkins said.

Hawkins used a vegetation rake to collect samples of vegetation from the limited open waters of East Lake Okoboji. Ice has stayed on the surface of the area lakes longer than usual, but Hawkins said it hasn't been enough to significantly deter the growth of curlyleaf pondweed.

The biologist said it's hard to predict whether Lakes residents and boaters will notice a difference as vacation season arrives.

"We're moving forward assuming growth is similar to last year," he added. "So, the plan is in place to try to deal with some of this and get some relief for lakeshore owners and boaters."

The DNR has a contract in place with Aquatic Environment Consultants for the application of Aquathol K. About 20 acres 10 acres in the north bay of East Okoboji and 10 acres in Lower Gar Lake will be treated with the chemical. Plans call for a single pass with a boat and the application should only take a few hours. The herbicide is applied under the water surface using a closed system.

State officials used a mechanical harvester to cut down 18 acres of the weed in 2017. Much of the shoreline harvesting in 2018 will take place south of the Highway 9 boat ramp.

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