Response of pinto and small red Mexican beans (Phaseolus vulgaris L.) to preplant-incorporated herbicides

Four field trials were conducted over a 2 year period at Exeter (2005, 2006), Harrow (2006), and Ridgetown (2006), Ontario, Canada, to evaluate the tolerance of pinto and small red Mexican (SRM) beans to the preplant-incorporated (PPI) application of trifluralin, dimethenamid, S -metolachlor, KIH-485, imazethapyr, and flumetsulam. All the treatments, including the untreated control, were maintained weed-free during the growing season. The PPI application of trifluralin, dimethenamid, and S -metolachlor resulted in minimal transient visual injury, with no adverse effect on the plant height, shoot dry weight, seed moisture content, and yield of the pinto and SRM beans. The PPI application of imazethapyr and flumetsulam, especially at the high rate, initially caused 13% injury and reduced the plant height and shoot dry weight by 15 and 28%, respectively, but these injuries were transient and had no effect on the seed maturity and yield of the pinto and SRM beans. The PPI application of KIH-485 caused 80% injury to the pinto and SRM beans and reduced the plant height, shoot dry weight, and yield. The dry bean maturity was also delayed. Based on these results, trifluralin, dimethenamid, S -metolachlor, imazethapyr, and flumetsulam, applied as PPI herbicides, have the potential to be used in a weed management program for pinto and SRM beans. However, KIH-485, applied as a PPI herbicide at the doses evaluated, does not have an adequate margin of crop safety for use in pinto and SRM bean production in Ontario.