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Weevil Project Postponed

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Conditions not suitable to stock weevils in Lake Pend Oreille this year.

Plans to stock beds of Eurasian water milfoil with a milfoil-munching weevil in Lake Pend Oreille have been postponed until next summer, Partners for Milfoil Control has announced.

While there is an estimated 650 acres of milfoil in Lake Pend Oreille and the Pend Oreille River, according to Bonner County’s most recent survey, most of it is in deeper water than usual and will take most of the summer to grow up to the water’s surface. The milfoil must be within one to two feet of the surface in order to stock the weevils, which are tiny aquatic insects that burrow into milfoil, weakening and killing it.

Partners for Milfoil Control formed earlier this year to raise money for the treatment of the noxious aquatic weed with the milfoil weevil. Fundraising of in-kind and direct contributions through private foundations, businesses, government entities and individuals successfully raised all of the funds needed for this summer’s project. The estimated cost per acre for stocking the weevils is about $2,000.

Members of the partnership – the Tri-State Water Quality Council, the Idaho Conservation League, Lake Pend Oreille Waterkeeper, and Sandpoint Mothers for Safe Water – had hoped to stock beds of Eurasian water milfoil this summer with thousands of weevils to provide peer-reviewed research into this biocontrol treatment option.

However, when the project’s researcher and weevil contractor toured the lake and river in July, it became clear that conditions were not suitable for stocking weevils this year.

Several factors may have led to this year’s sparse milfoil growth, including a 10-foot drawdown of the lake this past winter, an early freeze prior to the accumulation of an insulating layer of snow, late-season herbicide treatments this past fall, and an extended cool, rainy season in the spring.

“Based on these factors, weevils could not be stocked until September, which would likely give them only one generation this year.  We would like to stock by early August or sooner to increase the number of generations possible and optimize conditions for weevil growth,”  the project’s researcher, Dr. Michelle Marko of Concordia College in Moorhead, Minn., wrote in a letter to the Tri-State Council following her July visit.

 “It turned out to be that natural conditions made for good milfoil control this year,” said Susan Drumheller, Idaho Conservation League. “The downside is that it left few areas that were suitable for stocking weevils.”

Members of Partners for Milfoil Control expressed disappointment that the weevil project cannot move forward this summer, but postponing it until next year makes good sense, said Diane Williams of the Tri-State Water Quality Council, fiscal sponsor for the project.

“We need to responsibly spend the money raised for this project and to make sure that we’ve done everything possible to make it a success,” Williams said. “Stocking weevils this year would give us incomplete research information and would not achieve what we set out to do.”

In the meantime, Bonner County’s Public Works Department and the Aquatic Invasive Species Task Force have agreed to set aside about 65 acres from herbicide treatments this year so they will be available for weevil research sites next summer. The county is scheduled to treat about 330 acres of milfoil this year with herbicides.

“We appreciate the cooperation and support of Bonner County and the Task Force,” Williams said. “We are all anxious to launch this project and determine whether we can provide the county with a new tool for controlling milfoil in the Pend Oreille system.”

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Diane Williams Diane Williams is the Executive Director of the Tri-State Water Quality Council

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