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Lake’s initial milfoil treatment anticipated in early summer


March 29, 2011

The City of Lake Stevens and Snohomish County are expecting to implement a treatment this June or July to begin the eradication of the problematic non-native and invasive Eurasian watermilfoil (aquatic weed) from Lake Stevens.

Based on a summer 2010 survey conducted by the City and County, over 10 percent of the lake’s surface area had some level of milfoil growth. By August, the condition had worsened, with the milfoil growing into dense patches that impeded boating and swimming in the affected areas.

In 2010, the City received funding from the Washington State Department of Ecology’s (Ecology) Aquatic Weeds Management Fund to develop an Integrated Aquatic Vegetation Management Plan (IAVMP) for Lake Stevens.

The purpose of the IAVMP was to identify alternative methods to eradicate Eurasian watermilfoil and provide a recommendation. A steering committee guided the development of the IAVMP and was comprised of the Lake Stevens Citizens cost approximately $520,000 over a 10 year period. The highest portion of the cost, estimated at $186,000, will occur in 2011 (first year).

The initial treatment will involve the application of the herbicide over the entire milfoil affected area in June or July of this year, followed by spot treatments thereafter, if needed.

In each of the following years an investigation will be performed to monitor and identify spot treatment areas.

For the initial treatment, the City sought and was awarded a onetime State grant for $75,000. The eligibility requirement of this grant is that the implementation must occur after July 1, 2011.

The City and County will select a licensed professional applicator that will perform the treatment services. Prior to any application of triclopyr, a public outreach program will be implemented to educate and inform the public, including direct outreach to all homes adjacent to the lake and information on the City’s website (

The actual date of the 2011 herbicide application will be based on seasonal conditions that affect milfoil growth, including average temperatures and sunlight. Herbicide treatments are most effective during milfoil’s active growth period after the plants have significantly leafed out.

Typically the growth period in this region occurs in July. If treatment is performed too early or too late in the plant’s growth cycle, the effectiveness of the triclopyr is significantly reduced, requiring costly repeat treatments or higher rates of herbicide use.

The City is acting as the lead agency in the performance of the milfoil eradication services. The State has been notified of the City’s intent to implement the initial treatment, and the permits are in final process. It is anticipated that the City will be ready for the initial application in mid to late June. If you have questions, a copy of the City’s approved plan can be viewed at: Also, if you wish to learn more about triclopyr, Washington State Department of Ecology has an informative FAQ at:


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