Phytotoxicity assay for seed production using Brassica rapa L.

Although pesticide drift can affect crop yield adversely, current plant testing protocols emphasize only the potential impacts on vegetative plant growth. The present study was conducted to determine whether a plant species with a short life cycle, such as Brassica rapa L. Wisconsin Fast Plants®, can be used to indicate potential effects on seed production of herbicides applied at relatively low levels (e.g., low field application rates [FAR]). The effects of ≤0.1 × FAR of aminopyralid, cloransulam, glyphosate, primisulfuron, or sulfometuron applied 14 d after emergence (DAE), were evaluated for B. rapa grown in mineral soil in pots under greenhouse conditions. Effects were expressed as the effective concentration of the herbicide producing a 25% reduction in a response (EC25) based on nonlinear regression. Brassica rapa seed dry weight was reduced by sulfometuron at an EC25 of 0.00014 × a field application rate (FAR) of 53 g active ingredient (a.i.) ha −1 , primisulfuron at 0.008 (experiment 1) or 0.0050 (experiment 2) × FAR of 40 g a.i. ha −1 , cloransulam at 0.022 × FAR of 18 g a.i. ha −1 , glyphosate at 0.0399 × FAR of 834 g a.i. ha −1 , and by aminopyralid at 0.005 × FAR of 123 g a.i. ha −1 , but only for 1 of 2 experiments. Reduced seed production occurred at less than the FAR that reduced shoot dry weight with sulfometuron and primisulfuron, whereas neither aminopyralid, cloransulam, nor glyphosate affected shoot dry weight. A short life cycle form of B. rapa could be used to indicate reduced seed production with plants grown only 1 week longer (∼35 DAE) than as the current vegetative vigor test for nontarget herbicide effects on plants. Integr Environ Assess Manag 2010;6:725–734. © 2010 SETAC