USE OF RODEO(R) AND X-77(R) SPREADER TO CONTROL SMOOTH CORDGRASS (SPARTINA-ALTERNIFLORA) IN A SOUTHWESTERN WASHINGTON ESTUARY .1. ENVIRONMENTAL FATE

A I-ha plot with smooth cordgrass (Spartina alterniflora) at three loc ations in Willapa Bay, a southwestern Washington estuary, was aerially treated with 4.7 L/ha Rodeo(R) and 0.9 L/ha X-77(R) Spreader to deter mine the fate of the herbicide formulation. Rates of spray deposit on filter pads placed over treated intertidal mudflats did not differ amo ng locations for glyphosate and aminomethylphosphonic acid (AMPA); how ever, deposit rates for nonylphenol polyethoxylates (NPEO) did differ among locations. Glyphosate concentrations in sediment cores from trea ted mudflats declined 51 to 72% during 119 days posttreatment (DPT); N PEO concentrations in sediment declined (42%) between spray day and 14 DPT. The highest concentrations of glyphosate, AMPA, and NPEO in seaw ater were found in off-site samples collected from the leading edge of the first high tide after application. Glyphosate and AMPA concentrat ions in depth-integrated seawater samples declined 73 and 42%, respect ively, between the first high tide immediately following application a nd the second high tide at 1 DPT. Glyphosate concentrations in Spartin a stems from treated plots declined 91 to 99% between 1 and 28 DPT; wh ereas, AMPA declined (86 and >96%) during this period. Comparison of m aximum concentrations for glyphosate in seawater from this study with acute toxicity values in the literature indicates that under worst-cas e conditions direct effects to aquatic organisms would not be likely.