There are no restrictions on use of lake water for irrigation following treatment application according to the research that was used to develop the US EPA product label for both glyphosate and penoxsulam.
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Spanaway Lake is an important resource that provides many recreational, aesthetic and habitat benefits. In recent years, aquatic weed growth and harmful algal blooms have had a negative impact on the lake. In response, Pierce County worked with the community to develop an Integrated Aquatic Vegetation Management Plan (IAVMP) in 2020 to help address invasive aquatic weeds. The IAVMP identified chemical treatment with herbicides as the optimal strategy for weed control.
The target species for 2023 will be Fragrant Water Lily (Nymphaea odorata) and Curly Leaf Pondweed (Potamogeton crispus). Both are listed on the Washington State Noxious Weed Control Board Class C Noxious Weed list.
Fragrant Water Lily treatment will take place near shoreline areas of Spanaway Lake where the plant is present. To see a map of potential lily treatment areas, please visit https://arcg.is/09jaqT.
Curly Leaf Pondweed locations will need to be surveyed in spring of 2023 to determine the entire location and extent of the plant population. The treatment applicator will post signs in both the treated and potentially affected areas 24 to 48 hours before treatments are applied.
The applicator plans to use glyphosate and an approved aquatic surfactant, which is systemic herbicide that is effective on Water Lily.
The applicator may also use penoxsulam for control of the submerged Curly Leaf Pondweed. The brand of the penoxsulam product, Galleon SC, is classified as an EPA Reduced-Risk Aquatic Herbicide.
Both are fully approved for these uses by the US Environmental Protection Agency and Washington State Department of Ecology. Washington State Department of Ecology has issued an Environmental Impact Statement on the use of these products for aquatic weed control, which is available here: https://apps.ecology.wa.gov/publications/SummaryPages/0010043.html, and a Supplemental Environmental Impact Statement, which is available here: https://apps.ecology.wa.gov/publications/SummaryPages/1710020.html.
The applicator will mobilize a treatment boat to the lake, then target areas where noxious aquatic weeds are present.
Fragrant Water Lily treatment products (glyphosate) will be carefully applied using a spray solution from a handgun controlled by an experienced and licensed applicator. Curly Leaf Pondweed products (penoxsulam) will be applied via a solution emitted below the waterline through drop hoses controlled by an experienced and licensed applicator.
If you believe you have patches of Fragrant Water Lily in an area that is not identified in the most recent survey, please contact the Lake Management District at [email protected] or call (253) 798-4280 to have it added. You may be asked to provide photographs to assist in identification by the applicator.
No, there are no recreational water use restrictions for the proposed treatments. Neither the US EPA-approved product label nor the Washington Department of Ecology Aquatic Plant and Algae Management permit place a restriction on recreational water use for these products.
The applicator may, at their discretion, post signage at public access locations asking visitors to limit boat use during application, but only as a precaution to prevent boat wake interfering with optimal placement of the treatment products.
Yes. Both treatment products break down rapidly in water. Well studies have shown that these aquatic herbicides do not migrate through groundwater. In one study, a test well was drilled in sandy soil 20 feet from the shoreline and another drawdown well was placed beyond that to draw down water. There were no detections.
No. Water Lily treatment products (glyphosate) will be applied directly to the target plants using hand-operated devices that are not expected to create aerosols. Curly Leaf Pondweed products will be applied beneath the water surface and will not create aerosols. Further, the treatments will be applied by licensed applicators who are trained and experienced in preventing overspray and drift.
Washington State Department of Ecology has issued an Environmental Impact Statement on the use of these products for aquatic weed control, which is available here: https://apps.ecology.wa.gov/publications/SummaryPages/0010043.html, and a Supplemental Environmental Impact Statement, which is available here: https://apps.ecology.wa.gov/publications/SummaryPages/1710020.html.
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