Herbicide Programs for Managing Troublesome Weeds Using New Soybean Technologies

Soybean [Glycine max (L.) Merr.] cultivars will soon be available with stacked resistance to various herbicides, including glyphosate, glufosinate, dicamba, 2,4‐D, and several 4‐hydroxyphenylpyruvate dioxygenase (HPPD)–inhibiting herbicides. As many combinations of these herbicides have not been used in soybean preemergence (PRE) or postemergence (POST), two experiments were conducted in 2013 and 2014 at Keiser, AR, to evaluate various herbicide combinations for control of Echinochloa crus‐galli (L.) Beauv., Ipomoea lacunosa L., and Sida spinosa L. In the Herbicide Programs trial, 25 herbicide programs were evaluated that consisted of PRE herbicides followed by POST herbicides 3 to 4 weeks after (WA) the PRE application (EPOST), or 6 to 7 WA the PRE application (LPOST). The programs that contained EPOST herbicides controlled I. lacunosa, S. spinosa, and E. crus‐galli ≥95% 2 WA EPOST. Based on orthogonal contrasts, future programs utilizing an auxinic or HPPD‐resistance trait did not perform better than currently labeled soybean herbicides for control and weed density of E. crus‐galli and S. spinosa, but future programs outperformed current programs for control of I. lacunosa. In the PRE‐only trial, 19 herbicide treatments were evaluated 4 and 7 weeks after PRE (WAP). The greatest control 7 WAP for I. lacunosa and E. crus‐galli was obtained with isoxaflutole + S‐metolachlor + metribuzin, but this treatment did not differ from some other programs containing similar herbicides (e.g., S‐metolachlor + mesotrione). Flumioxazin + pyroxasulfone, a treatment currently labeled in soybean, provided the greatest control (77%) of S. spinosa, but did not differ from isoxaflutole + S‐metolachlor + metribuzin (71%). Although new herbicide technologies that allow dicamba, 2,4‐D, mesotrione, or isoxaflutole may not necessarily improve control of all problematic weeds compared with currently labeled programs, increasing the herbicide sites of action applied in soybean systems will help manage the spread of herbicide resistance.