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Sensitivity of Native Aquatic Plant Species to Imazamox (Clearcast) and Penoxsulam (Galleon)

Madsen, J. D., Wersal, R. M., & McLaurin, C. S. (2011). Sensitivity of Native Aquatic Plant Species to Imazamox (Clearcast) and Penoxsulam (Galleon). Western Aquatic Plant Management Society Annual Meeting. Westminster, CO.


The objectives of this study were to determine the dose response of selected submersed and emergent native species to both imazamox (Clearcast™) and penoxsulam (Galleon™); and to evaluate exposure time response to imazamox. Studies were conducted in a mesocosm facility for 12 weeks beginning in June 2010, and conducted as completely randomized designs in 300 gallon tanks. Emergent plants were arrowhead (Sagittaria latifolia.), bulrush (Scirpus acutus), and white waterlily (Nymphaea odorata). The native submersed species were coontail (Ceratophyllum demersum), sago pondweed (Stuckenia pectinata), vallisneria (Vallisneria americana), elodea (Elodea canadensis), and American pondweed (Potamogeton nodosus); and Eurasian watermilfoil (Myriophyllum spicatum) to document invasive species response. Imazamox was applied at 200, 100, 50, and 25 parts per billion (ppb) for 1, 3, or 7 days. Penoxsulam was applied to the water column at 3, 6, and 12 ppb as a static exposure for 60 days. At 12 weeks after treatment (WAT), submersed plants were largely unaffected by imazamox across concentration and exposure times, with the exception of elodea. Arrowhead and bulrush were not affected 12 WAT with imazamox, but white waterlily was reduced at the maximum rate and exposure time with imazamox. Most native submersed plants were unaffected by penoxsulam exposure. Although reductions in biomass were observed for elodea, the plants were not chlorotic or necrotic; biomass reductions were due to the growth regulating effect of low doses of imazamox and penoxsulam. Floating and emergent plants were not affected by penoxsulam at the concentrations tested.

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