John Wiley & Sons, Ltd.

Effects of low levels of herbicides on prairie species of the Willamette Valley, Oregon

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The relative sensitivity of 17 non‐crop plant species from Oregon's Willamette Valley was determined in response to glyphosate, tribenuron methyl (tribenuron) and fluazifop‐P‐butyl (fluazifop) herbicides. For glyphosate; Elymus trachycaulus, Festuca arundinacea, Madia elegans, Potentilla gracillis and Ranunculus occidentalis were the most sensitive species, based on a concentration calculated to reduce shoot dry weight by 25% (IC25 values) of 0.02 to 0.04 × a field application rate (FAR) of 835 g active ingredient hectare (g a.i. ha−1) . Clarkia amoena and Lupinus albicaulis were the most tolerant to glyphosate, with IC25 values near the FAR. Clarkia amoena, Prunella vulgaris and Ranunculus occidentalis, were the most sensitive to tribenuron with IC25 values of 0.001 to 0.004 × FAR of 8.7 g a.i. ha−1 for shoot dry weight. Five grass species were tolerant to tribenuron with no significant IC25 values. For fluazifop, two native grasses, Elymus trachycaulus and Danthonia californica, were the most sensitive species with IC25 values of 0.007 and 0.010 × FAR of 210 g a.i. ha−1, respectively, for shoot dry weight; while a native grass, Festuca roemeri and nearly all forbs showed little or no response. These results also indicated that the three introduced species used in the present study may be controlled with one of the tested herbicides: glyphosate (Festuca arundinacea), tribenuron (Leucanthemum vulgare), or fluazifop (Cynosurus echinatus), respectively. Environ Toxicol Chem © 2013 SETAC

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