2006 Sonar Herbicide Treatments on Lake Pend Oreille Continue to Provide Relief

In 2006, Aquatechnex biologists implemented the largest aquatic herbicide treatment program targeting Eurasian Milfoil that has been performed in the Western United States.  Lake Pend Oreille and the Pend Oreille River had in excess of 6,000 acres of littoral area heavily impacted by this invasive aquatic species.  The State of Idaho Legislature passed funding for the control of this noxious weed and the Bonner County Weed Department who is charged with managing these waters solicited proposals to manage this growth.  Aquatechnex was selected as the most qualified respondent to that RFP request and we designed a program using a number of different control strategies.

As there were extremely large areas of the lake heavily infested with Eurasian Milfoil, we felt that Sonar Aquatic Herbicide was an ideal fit.  Sonar can be selective for Eurasian Milfoil when the dose is controlled.  Many beneficial native aquatic plants that are replaced by milfoil are not as sensitive as milfoil is to this product.  We designed a program that applied Sonar Precision Release herbicide to approximately 3,000 surface acres across the 90 miles of shoreline we were managing.  Sonar is a very slow acting herbicide and the majority of these acres were rated as controlled at the end of the 2006 season.  Some smaller areas showed some remaining milfoil growth, but we collected samples and sent them to SePRO’s Research and Technology Campus for evaluation.  A plant assay indicated that the herbicide levels in the plants were such that they would respond to the treatment as well.

We have the opportunity to inspect a number of these larger sites in early August of this year, this is the sixth season post treatment.  These treatment areas remain largely milfoil free and there are very diverse stands of native aquatic plants throughout the 2006 treatment polygons.  The few milfoil plants that are present are a result of fragments moving in from other areas of the system and from upstream in the Clark Fork River system in Montana.

This treatment was very economical the year of application.  The cost per acre for herbicide in 2006 was approximately $586.00.  As control has resulted in over 5 years of control, the cost per acre for the results delivered up to this point are $99.00 per acre.  This technology continues to benefit the lake users and the environment and has delivered signficant control over six seasons.  It has also allowed the native plant communities to recover these areas that used to be a monoculture of an invasive aquatic species.

We will be assisting the State target some remaining growth this September as part of our ongoing program to manage this weed in the lake.  For more information go to www.pomilfoil.wordpress.com



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