More focused milfoil treatments planned

SANDPOINT — Herbicide treatments of Eurasian milfoil in Lake Pend Oreille this summer are expected to be later in the season and more limited than in years past.

There is also a suite of research projects planned to learn more about how herbicides disperse in difficult-to-treat areas, to control the aquatic noxious weed using weevils and to target a relatively new invader — flowering rush.

Tom Woolf, an aquatic plants manager for the Idaho State Department of Agriculture, said previous milfoil-control efforts have knocked back the lake’s infestation from 5,000 acres to less than 1,000.

“What remains is the most difficult to treat,” Woolf said on Thursday.

Woolf said the Pend Oreille could prove to be the most challenging lake in the world to treat because of its depths, water movements, drinking water intakes and upstream inputs.

“Funding is more and more limited, so we have to prioritize where we treat,” he said. “We realize we have to walk away from some areas because of the various issues.”

ISDA, which is spearheading this summer’s treatment program with collaboration from Bonner County, has not decided yet which herbicides it will use. Woolf said treatments sites will be prioritized with local input, but the focus will be high-use, high-priority sites.

Meanwhile, U.S. Army Corps of Engineers is funding a research project to dial in treatments in areas of deep water where there is water exchange.

Resource management firms TetraTech and AquaTechnex will conduct a dye/herbicide study with assistance from chemical manufacturer SePRO to determine the efficacy of treatments in deep, dynamic sections of the lake.

“We will be able to go to a challenging site and determine whether the conditions at the site are suitable for herbicides,” said Terry McNabb of AquaTechnex.

The research team plans to identify two 10-acre sites to conduct the research, which is tentatively slated for early or late August.

Backers of a delayed study to determine the effectiveness of using weevils to beat back milfoil in the Pend Oreille are hoping to get the project off the ground. The good news is the project is being enhanced with federal stimulus funding; the bad news is that some factors that delayed the project last year are at play this year.

The weevil project was tabled last year because plant growth was inhibited by a deep drawdown of the lake and a dryer, colder winter that did not provide the plants with an insulating layer of snow.

The federal funding would enable two years of weevil stocking and three years of research. But if that money can’t be spent by the end of the year, it would lose the funding and allow for only one year of stocking and two years of research.

“The idea is to get them out there by mid-August or so,” Diane Williams of the Tri-State Water Quality Council, the weevil project’s fiscal manager, said of the weevils.

The corps is also partnering with various local and federal agencies to determine the best way to nip flowering rush in the bud. The plant migrated to Idaho via the Clark Fork River and has been detected as far downstream as Laclede.

Resource officials have gone after the newcomer with the vigor a mobbed-up bookie would employ to go after somebody who won’t pay up. They’ve tried digging it up and burning it up when the lake is down.

“I call it the cockroach of the plant kingdom,” said Betsy Hull, a natural resource specialist with the corps at Albeni Falls. “It won’t die.”

Hull and other partners plan to suffocate flowering rush with bottom barriers, with much of the effort concentrated in the Clark Fork Delta.