Tolerance of azuki bean to herbicides applied preplant for weed control in a strip-tillage cropping system

Five field experiments were conducted at Huron Research Station near Exeter, Ontario, Canada, during 2018 to 2020 to assess the tolerance of strip-till-grown azuki bean to various preplant (PP) herbicides. The herbicides selected have activity on glyphosate-resistant (GR) Canada fleabane, an emerging weed biotype in strip-till azuki bean production. Saflufenacil, metribuzin, 2,4-D ester, saflufenacil + metribuzin, saflufenacil + 2,4-D ester, metribuzin + 2,4-D ester, and saflufenacil + metribuzin + 2,4-D ester, applied PP 1 week before seeding, at the proposed label rate (1X) and twice that rate (2X) caused as much as 6%, 5%, 6%, 7%, 8%, 10%, and 13% visible azuki bean injury. The herbicide-induced azuki bean injury was transient and had no effect on plant density, aboveground dry biomass, height, maturity, and yield except for the dry biomass which was reduced by 28% with metribuzin + 2,4-D ester and 36% with saflufenacil + metribuzin + 2,4-D ester at the 2X rate and azuki bean height which was reduced 9% at the 2X rate with saflufenacil + metribuzin + 2,4-D ester. Based on these results, saflufenacil, metribuzin, 2,4-D ester, saflufenacil + metribuzin, saflufenacil + 2,4-D ester, and metribuzin + 2,4-D ester applied PP have potential for GR Canada fleabane control in strip-till azuki beans. However, there is not enough crop safety for using a three-way tankmix of saflufenacil + metribuzin + 2,4-D ester, applied PP, in azuki bean production.