Flowering rush used to be a gloomy presence on the Detroit Lakes City Beach, mucking up the view and, literally, mucking up the lakebed, since the aquatic invasive plant slowly turns the ecology of a lake more swampish.
Now, lily pads and sandy lake bottom are again sheltering fish and providing spawning habitat: In fact, flowering rush has now been reduced to the point that it was kind of hard recently to find a sample to send to another state, said Pelican River Watershed District Administrator Tera Guetter.
“We only treated 20 acres this spring -- that’s unbelievable," Guetter said, “down from 200 acres when we started doing these full-scale treatments in 2013.”
About 10 years ago, the flowering rush was at its worst.
“You remember those days,” she said. “Nobody wanted to swim in the lake -- triathlon athletes complained that they had to swim through the reeds,” Guetter said.
The watershed district tried cutting it as a form of short-term control, and when that didn’t work, people took matters into their own hands.
It was called “Crush the Rush,” an effort to harvest local manpower to pull out the hated flowering rush by hand. “Lakeshirts developed the logo,” Guetter said. “The Lake Detroiters (lake association) spearheaded it.”
That citizen involvement and citizen outcry “motivated us to say ‘we’ve got to get serious here,’” Guetter said. “That’s why, in 2010, we paid for this big summit in St. Paul -- all these entities came together to decide what to do.”
The watershed district and the city eventually decided to battle the flowering rush invasion through science.
“I don’t think anybody else has done this kind of concentrated effort,” Guetter said. And that kind of cutting-edge approach doesn’t come cheap.
Extensive research and testing, done between 2010 and 2016, cost about $750,000, with $450,000 of that local dollars and the rest state and federal dollars.
That research spanned the gamut, from Army Corps of Engineers water tank studies to extensive real-life application on lake test plots. Multiple studies were done and all were published in scientific journals, “which made the DNR more comfortable,” with herbicide being applied to lakes and rivers that held flowering rush, Guetter said.
The tank studies narrowed the solution down to two chemicals -- imazapyr and diquat, Guetter said.
Researchers thought they had a winner with the imazapyr, but after three years, they realized that fish just wasn’t going to bite, and switched their focus to the herbicide that eventually proved successful -- diquat.
It had to be applied in the right way, at the right concentration, in the right water depth, and at the right time of year.
Once the recipe was perfected, the flowering rush could be successfully attacked without harming the native bulrush. Flowering rush hasn’t gone away, but it has greatly thinned out or disappeared in many areas it once dominated: Deadshot Bay, Big and Little Detroit lake, Lake Sallie, Lake Melissa, and to a lesser extent, Muskrat Lake and Mill Pond, where currents make application more difficult.
Since diquat is the only arrow in its sling, the watershed district is now careful to “skip a year,” and otherwise apply it in a way that minimizes the risk of flowering rush becoming resistant to the herbicide, Guetter said.
So far, the results in the long war against flowering rush have been sort of stunning. “I’m so excited. You just don’t see this (kind of success) in this world,” Guetter said. “I think people forget how our lake used to look.”
The Pelican River Watershed District plans to enter its flowering rush success story in a statewide watershed district award competition.
“Detroit Lake is on the map,” she said. “It took the village on this one.”