Spray application of 24 and 46 g ha−1 MON 37500 was used in efficacy studies, and vacuum infiltration or droplet application of radiolabeled MON 37500 was used in metabolism studies to evaluate temperature and soil moisture on MON 37500 efficacy and metabolism. Day/night temperatures before vs. after application of MON 37500 of 25/23 vs. 25/23, 25/23 vs. 5/3, 5/3 vs. 25/23, and 5/3 vs. 5/3 C were evaluated for the efficacy study, whereas day/night temperatures of 5/3 and 25/23 C were used for the metabolism study. Soil moisture of one-third and full pot capacities was evaluated for both studies. No Triticum aestivum injury was observed at the different temperatures or soil moistures because of rapid metabolism of MON 37500 by T. aestivum. Weed control was greater when the temperature after application was 25/23 C or soil moisture was at full pot capacity than when the temperature was at 5/3 C after application or soil moisture was at one-third pot capacity. Susceptibility to MON 37500 was greatest for Bromus tectorum, moderate for Avena fatua, and least for Aegilops cylindrica. This pattern of susceptibility for the weed species was related to their ability to metabolize MON 37500. Aegilops cylindrica metabolized more MON 37500 in the first 24 h than did A. fatua, whereas B. tectorum metabolized the least MON 37500. Cool air temperatures decreased MON 37500 metabolism in all species, whereas soil moisture had no effect.
Nomenclature: MON 37500, 1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea; Triticum aestivum L., spring wheat ‘Len’; Aegilops cylindrica Host. AEGCY, jointed goatgrass; Avena fatua L. AVEFA, wild oat; Bromus tectorum L. BROTE, downy brome.
