Abstract: MON 37500 was registered in 1999 for weed control in wheat and has the potential to injure following crops. Therefore, growth chamber experiments were conducted to determine the effect of soil properties on the phytotoxicity of MON 37500 residues, the relative tolerance of several potential rotational crops, and the joint effect of MON 37500 residues plus other herbicide residues on a susceptible crop. In 13 Alberta soils, the concentrations of MON 37500 and triasulfuron that reduced canola and barley dry matter by 50% (GR50) were correlated with soil organic matter (OM) and pH. The relationship that best described the effect of soil organic matter on GR50 for each herbicide–crop combination was GR50 = a b(OM)2. There was no significant improvement in r2 when pH and clay content were included in the equation. For soils with 2 and 10% OM content, predicted GR50 values for canola in MON 37500–treated soil are 2 and 26 ηg/g soil, respectively. Little injury to following canola is predicted in soils with OM contents > 4.5%. At similar concentrations, following crops such as canola, flax, lentil, and oriental mustard are predicted to be injured less by MON 37500 than by triasulfuron. The effect of combined residues of MON 37500 with triasulfuron, imazethapyr, or metsulfuron should be additive.
Nomenclature: Imazethapyr; metsulfuron; MON 37500, 1-(4,6-dimethoxypyrimidin-2-yl)-3-(2-ethanesulfonylimidazo[1,2-a]pyridine-3yl)sulfonylurea; triasulfuron; barley, Hordeum vulgare L.; canola, Brassica napus L.; flax, Linum usitatissimum L.; lentil, Lens culinaris Medic; oriental mustard, Brassica juncea L.; wheat, Triticum aestivum L.
Additional index words: Crop rotation, herbicide residue, pH, soil organic matter.
Abbreviations: GR50, growth measurement corresponding to 50% of the untreated; OM, soil organic matter.