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Assessing the risk of Glyphosate to native plants and weedy Brassicaceae species of North Dakota
Citation:
OLSZYK, D. M., T. G. PFLEEGER, E. LEE, C. A. BURDICK, AND M. PLOCHER. Assessing the risk of Glyphosate to native plants and weedy Brassicaceae species of North Dakota. Presented at SETAC North America Annual Meeting, New Orleans, LA, November 19 - 23, 2009.
Impact/Purpose:
This study was conducted to determine the ecological risk to native plants and weedy Brassicaceae species which may be growing in areas affected by off target movement of glyphosate applied to glyphosate-resistant canola (Brassica napus).
Description:
This study was conducted to determine the ecological risk to native plants and weedy Brassicaceae species which may be growing in areas affected by off target movement of glyphosate applied to glyphosate-resistant canola (Brassica napus). Ten native grass and forb species were selected based on their importance in prairie areas of North Dakota and four Brassicaceae species (Brassica juncea, B. nigra, B. rapa and Sinapis arvensis) were selected based on their ability to cross with B. napus. Greenhouse-grown seedlings were treated with a sequence of rates ≤ 0.1 × a field application rate (FAR) of 830 g active ingredient / HA of glyphosate which simulates near-field pesticide drift deposition rates. Shoot height and dry weight were measured 14 days after treatment, Data were subjected to analysis of variance and Dunnett's test to obtain the no effect concentrations (NOEC) and nonlinear regression to obtain the effective concentration producing a 25% reduction in the plant response (EC25). Seven native species had NOEC values of 0.018 × FAR and EC25 values for height and/or shoot dry weight within drift levels of glyphosate between approximately 0.01 and 0.1 × FAR. Dalea purpurea and Nassella viridula were the most sensitive with EC25 values of shoot dry weight of 0.014 and 0.017 × FAR, respectively. Three native species showed little or no affect of glyphosate on shoot growth (Andropogon gerardii, Pascopyrum smithii and Schizachyrium scoparium). The Brassicaceae species responded similarly to glyphosate with NOEC values of 0.018 × FAR and EC25 values between approximately 0.01 and 0.1 × FAR. This study illustrated a procedure for evaluating the risk to non-target non-crop species from glyphosate drift, and indicated that drift concentrations between 0.01 and 0.1 × FAR can affect growth and potential competitiveness of native plants and species sexually compatible with glyphosate-resistant B. napus.