2021 Milfoil Treatment Information Loon Lake- http://loonlakewa.wordpress.com/

By Lee Evans, Chairman

Loon Lake Lake Management District (LMD)

The Loon Lake Lake Management District (LMD) has been quite active this season with an early June survey followed up by a June 18 ProcellaCOR herbicide treatment of 10.2 acres. Phase 2 included a second survey and inspection on July 9, with a follow-up ProcellaCOR treatment of 22.5 acres on July 15. A third survey and inspection in August with a third application (Phase 3) of a granular Renovate 3 for the milfoil located in the deeper areas of the lake is also planned.

The Phase 1 early June activity was twofold: (1) to inspect the effectiveness of the one-year post-treatment results for DOE grant final report and (2) to target the earliest new milfoil growth.

Phase 2 survey was to identify areas missed or that had not been visible in the June survey.

Phase 3 will concentrate on the milfoil located in the deeper waters that are more difficult for liquid herbicides to be effective. Herbicide efficacy in aquatic environments is influenced primarily by three conditions: (a) herbicide concentration in the water, (b) length of time the targeted plant species remains exposed to a herbicide concentration, and (c) the growth stage of the targeted plant at the time of treatment. Understanding the length of time and concentration exposure necessary for an herbicide mode of action to effectively target invasive weeds is critical to planning effective treatments.

June 30, 2020, concluded the Washington State Department of Ecology water quality grant to explore effective methods to treat Loon Lake hybrid milfoil.  The link for the final report (Loon Lake Hybrid Milfoil Control Project Final Report) will give the history and detail of the three-year study undertaken by the Loon Lake LMD, Stevens County, and our aquatic partner, Aquatechnex.

Grant Report Conclusions

“The 2019 ProcellaCOR EC herbicide treatment performed July 9th resulted in excellent overall control of hybrid milfoil plants targeted in Loon Lake. At the end of the season in 2019, milfoil plants with live tissue were not present visually within any of the treatment areas of the lake. In confirmation of the visual observations, the point intercept analysis showed either dead plants or severely injured plants present. At one year, post-treatment visual inspection of treatment sites showed little to no milfoil present. In a few locations, there were scattered stems extremely low in the water column with injury symptoms present.

Point intercept analysis: 87% of the points showed zero milfoil present, and 13% has milfoil present, in many cases with injury symptoms and at a much lower density than pre-treatment. There are other areas in Loon Lake that were not subject to herbicide treatment in 2019 that are exhibiting a level of milfoil plants that should be targeted in the early summer of 2020.”

I would like to extend a thank you to the members of the LMD Board and to Stevens County. COVID-19 has made it difficult for our Board to meet and formulate the planning necessary to accomplish the goals for this season. It has been the year of emails, phone calls, and text messaging when group discussions were necessary.