Pre-emergence herbicides for potential use in pinto and small red mexican bean (Phaseolus vulgaris) production

Four field trials were conducted over a two-year period at Exeter (2005, 2006), Harrow (2006) and Ridgetown (2006), Ontario to evaluate the tolerance of pinto and Small Red Mexican (SRM) beans to the pre-emergence application of dimethenamid-p at 693 and 1386 g ai ha−1, s-metolachlor at 1600 and 3200 g ai ha−1, pyroxasulfone at 209 and 418 g ai ha−1, imazethapyr at 75 and 150 g ai ha−1, linuron at 1125 and 2250 g ai ha−1, flumetsulam at 70 and 140 g ai ha−1 and cloransulam-methyl at 35 and 70 g ai ha−1. All treatments including the non-treated control were maintained weed free during the growing season. Dimethenamid-p and s-metolachlor, especially at high doses, caused up to 19% visual injury to pinto and SRM, but these injuries were transient and had no effect on maturity and yield. Pyroxasulfone and linuron caused as much as 33% visual injury and reduced plant height, shoot dry weight and yield by up to 29, 36 and 25%, respectively. Imazethapyr, flumetsulam and cloransulam-methyl caused less than 5% visual injury and had no adverse effect on plant height, shoot dry weight, seed moisture content and yields of pinto and SRM beans. Based on these results dimethenamid-p, s-metolachlor, imazethapyr, flumetsulam and cloransulam-methyl applied pre-emergence have potential for inclusion in a weed management program for pinto and SRM beans. However, pyroxasulfone and linuron, applied pre-emergence at the doses evaluated do not have an adequate margin of crop safety for use in pinto and SRM bean production.