Eurasian Milfoil Controlled in Two Washington Lakes

Over the past three years, Aquatechnex biologists have been assisting agencies in Washington State management the invasive aquatic weed Eurasian Milfoil.  Two of these major projects have reduced the Eurasian Milfoil populations from in excess of hundreds of acres to scattered plants that divers can easily remove.

Lake Tapps is a 22oo acre reservoir off the White River in suburban Seattle Washington.  This shallow system was established to produce hydro power, but relicensing costs prompted the utility to sell the system to the Cascade Water Alliance.  The lake has for years been fully developed with lake front homes.  Eurasian Milfoil had been introduced and expanded to the point of dominating the entire littoral area of the lake.

The key to targeting this infestation was to develop and implement a plan using two aquatic herbicide formulations that focus on Eurasian Milfoil.  In 2010, our team implemented a treatment program with Sonar Precision Release aquatic herbicide.  We made three applications at two week intervals and monitored the levels present to insure exposure over 6-8 weeks.  That treatment focused on all of the infested bays on the lake system. provides a summary of this program.  In 2011, our team switched our focus to areas that were smaller and more exposed to dilution.  We selected Renovate OTF, a granular controlled release formuation of Triclopyr, this product is selective for Eurasian Milfoil.  At the start of 2012, the lake is free of this noxious weed, levels are so low that diver removal will be adequate to move forward. provides more background.

The second system is Lake Stevens north of Seattle.  This 1200 acre lake system had approximately 135 acres of solid Eurasian milfoil at the start of the 2011 summer season.  The plan developed for this project called for the use of Renovate OTF.  Aquatechnex team targeted this growth using precision application systems.  At the mid point in the 2012 season, survey efforts have shown that only scattered plants remain and diver actions again will be used to remove the remaining plants.

These technologies were used by our firm on Lake Pend Oreille through work performed for Bonner County and funded by the ISDA program.  Many Sonar areas treated in 2006 remain free of Eurasian Milfoil to this day, and other sites are just now starting to show signs of increased impact.  Renovate OTF is also a preferred formulation of triclopyr herbicide because it can control Eurasian Milfoil using lower amounts of herbicide, something that new NPDES permits require.


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