POLSON – A noxious weed called flowering rush has clogged more than 2,000 surface acres of Flathead Lake, and experts are warning that if left unchecked the invasive plant could dramatically change the ecology of the lake.
Peter Rice, a researcher with the University of Montana’s Division of Biological Sciences, and Virgil Dupuis, the extension director at Salish Kootenai College, are working together to study ways of controlling the weed.
“We’ve gone from one known infestation in 1964 to uncountable numbers in less than 50 years,” Rice said. “You can imagine, if it goes unchecked, what the lake will look like in 200 years. It will entirely change the ecology of Flathead Lake.”
The plant has already spread into the Clark Fork River and all the way to Lake Pend Oreille in Idaho, he said.
While the pair is studying ways to control the spread of flowering rush, they say their funding is extremely limited. And they say that actually enacting any control methods would be up to the governments responsible for the lake bed — Flathead County, the state of Montana and the tribes within the boundaries of the Flathead Indian Reservation.
But the first step has already been taken: Montana, Idaho, Washington and Oregon have all declared the plant a noxious weed.
“Washington and Oregon didn’t even know what it was until we contacted them,” Rice said.
The men say they’ve found that herbicides can knock the flowering rush down for a year and a half, but it does come back. The two schools have spent three years studying controlling techniques in a greenhouse before applying them to test plots near the Ducharme Fishing Access. The testing scheduled for this spring was delayed because of the weather — the herbicides must be applied while the lake is down but the weeds are between 8 and 10 inches tall, and the cold weather meant the weeds didn’t reach the required height before water levels rose.
They’re also testing water column injections, where computer-controlled weighted hoses pulled behind a boat inject precise amounts of herbicides. But that method is expensive, costing between $1,300 and $2,400 per acre, Dupuis said.
Rice says the weed can’t be eliminated completely, but it could be managed and contained to high-priority sites.
Left unchecked, the weed could spread all the way to the Pacific Ocean via the Columbia River system, Rice said. It’s already eaten up several swimming and water skiing spots on the Flathead, clogging docks and boat slips. The plant also provides habitat for great pond snails, which host the parasites responsible for swimmer’s itch.
“It’s a horrific problem,” said June Hatleberg, who lives on Hughes Bay about three miles south of Lakeside. “The area grows larger and every year all the dead leaves decay and compost, and the bay gets shallower. We used to water ski in the bay, but you can’t anymore. It’s hard to get a boat in and out. And the quality of the water is bad.”