Idaho County Stands by Aquatic Herbicides

Published July 1, 2007

Guided by the findings of a blue-ribbon panel of aquatic plant managers, Bonner County, Idaho commissioners agreed on May 8 to continue using aquatic herbicides as the centerpiece of their program to eradicate Eurasian milfoil.

Last summer, Idaho communities benefitted from a newly established state fund to wage war on invasive milfoil. Eurasian milfoil is a highly aggressive aquatic weed native to Europe and Asia. It takes root at the bottom of ponds and lakes and sends long, spindly tendrils to the water’s surface.

Near the surface, the plants form a dense mat of entangling weeds that deprives the water of oxygen and chokes out native plants and animals. The mat of weeds emits a noxious order and is often thick enough to make swimming, boating, and other recreation hazardous or even impossible.

Comprehensive Review

Local water management districts in Idaho and nationwide use aquatic herbicides as their weapon of choice against milfoil.

To ensure aquatic herbicides are as effective and safe for the environment as advertised, the Idaho State Department of Agriculture (ISDA) in September 2006 assembled a panel of aquatic plant experts from across the country to review the state’s Eurasian Watermilfoil Control Program. The panel completed its review in December.

County Approves Herbicides

Armed with the panel’s findings and recommendations, Bonner County commissioners approved a plan to spend $1.7 million of its $1.8 million 2007 milfoil budget on aquatic herbicide applications. The remaining money will be spent on divers hand-pulling weeds and installing weed barriers on lake bottoms.

The commissioners’ decision implements a recommendation from the county’s Aquatic Invasive Species Task Force, which recommended the program on May 7.

Todd Crossett cast the lone dissenting ballot among the Bonner County commissioners. Crossett asserted more funds should have been directed to biological controls such as weevils that feed on milfoil.

Herbicide Success Story

But “biological controls do not eradicate,” noted Matt Voile, manager of the ISDA noxious weeds program. “All of this money that came through the legislature to eradicate milfoil, the language by the legislature very specifically states that we can only fund eradication technologies.

“There is not a biological scientist out there anywhere that will tell you that biological control is an eradication tool,” Voile continued. “Biological controls merely help contain the problem, but do not eradicate it.

“Even at its very best, research shows biological controls affect only the top 18 inches of milfoil,” Voile explained. “It by no means kills the plant. In North Idaho we have very pristine lakes with water clarity of more than 25 feet deep. When we talk about dealing with only the top 18 inches and leaving the remaining 24 feet unaffected, this is clearly not a viable eradication option. The language of the statute specifically says the money must be spent on eradication.”

Voile emphasized that aquatic herbicides have an established record of successful eradication without any adverse environmental effects.

“Last year in the north end of the state, herbicides were our predominant weapon,” Voile observed. “No negative environmental effects were reported to the Department of Environmental Quality, and we did redundant water sampling to verify this. We had investigators on the boat and at the dock for every herbicide application. I myself was present at many of these. We take extensive measures to verify that no environmental damage is done.

“In the lakes that have been treated, we have had seven or more native plants that have taken the lake back,” Voile noted. “We are finding very limited milfoil but abundant native plants. We are having good native plant response.”

James M. Taylor ([email protected]) is senior fellow for environment policy at The Heartland Institute and managing editor of Environment & Climate News.