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Sensitivity of Native Aquatic Plant Species to Imazamox and Penoxsulam

Madsen, J. D., Wersal, R. M., & McLaurin, C. S. (2011). Sensitivity of Native Aquatic Plant Species to Imazamox and Penoxsulam. Midwest Aquatic Plant Management Society Annual Meeting. Grand Rapids, MI.


The goal of managing invasive aquatic plant species is to control the target invasive plant and not affect native plant species, which is often referred to as selective control. The objectives of this study were to determine the dose response of select submersed and native species to both imazamox and penoxsulam; and to evaluate exposure time relationships of these native plants to imazamox. Two studies were conducted in a mesocosm facility located at the R.R. Foil Plant Science Research Center, Mississippi State University for 12 weeks beginning in June 2010. The studies were conducted as completely randomized designs using 78, 300 gallon tanks for the imazamox trial, and 24, 300 gallon tanks for the penoxsulam trial. Emergent plants used for these trials were: arrowhead (Sagittaria latifolia.), bulrush (Scirpus acutus), and white waterlily (Nymphaea odorata). The submersed species used were coontail (Ceratophyllum demersum), sago pondweed (Stuckenia pectinata), vallisneria (Vallisneria americana), elodea (Elodea canadensis), American pondweed (Potamogeton nodosus), and Eurasian watermilfoil (Myriophyllum spicatum). Imazamox was applied to the desired concentrations of 200, 100, 50, and 25 parts per billion (ppb). Plants were exposed to imazamox for 1, 3, or 7 days, after which water was drained from the tanks and replaced with fresh water. Penoxsulam was applied to the water column at the concentrations of 3, 6, and 12 ppb. Penoxsulam concentrations were held as a static exposure for 60 days, after which the water was drained in all tanks and replaced with fresh untreated water. At 12 weeks after treatment (WAT), all plants were harvested by cutting stems at the sediment surface, dried at 70 C for at least 72 h, and weighed. 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. Native submersed plants were unaffected by penoxsulam exposure, with the exception of elodea, which was reduced at all concentrations. Floating and emergent plants were not affected by penoxsulam treatments at this concentration. Future research will examine imazamox and penoxsulam effectiveness on curlyleaf pondweed.

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