Effect of herbicide application timing and sequence on waterhemp (<i>Amaranthus tuberculatus</i>) and common lambsquarters (<i>Chenopodium album</i>) control, Enlist E3® soybean yield, and economic returns

Abstract Enlist E3® soybean is resistant to 2,4-D, glyphosate, and glufosinate, allowing postemergence applications of these herbicides sequentially or as tank mixes. The objectives of this experiment were to evaluate the effect of postemergence herbicide application timing and sequence with or without a preemergence application of micro-encapsulated acetochlor on waterhemp and common lambsquarters control, soybean yield, and economic returns. Field experiments were conducted in Rosemount and Franklin, Minnesota, in 2021 and 2022. Site, herbicide application timing, and sequence influenced weed control, yield, and profitability. In Rosemount, preemergence followed by (fb) two-pass postemergence programs, including 2,4-D + glyphosate applied at mid-postemergence with or without S -metolachlor, resulted in ≥95% waterhemp control at 28 d after late postemergence application. In Franklin, where weed density was lower, two-pass postemergence programs, regardless of preemergence application that included at least one application of 2,4-D + glyphosate (with or without S -metolachlor), provided ≥97% control of waterhemp and common lambsquarters at 28 d after late postemergence. The level of control was comparable to that of a preemergence herbicide fb a mid-postemergence application of 2,4-D + glyphosate + S -metolachlor at that site. In Rosemount, including acetochlor as the preemergence herbicide in the preemergence fb postemergence programs improved soybean yield by 32% and partial returns by US$384.50 ha −1 compared to postemergence herbicides–only programs. In contrast, the preemergence application did not affect yield or profitability in Franklin. The highest soybean yield (2,925.7 kg ha −1 ) in Rosemount resulted after glufosinate was applied early postemergence fb 2,4-D + glyphosate applied mid-postemergence. This yield was comparable to that of glufosinate applied early postemergence fb 2,4-D + glyphosate + S -metolachlor applied mid-postemergence and the two-pass glufosinate (early postemergence fb mid-postemergence) program, highlighting the importance of early season weed control. In Franklin, 2,4-D + glyphosate + S -metolachlor (applied mid-postemergence) fb glufosinate (applied late postemergence) provided a yield that was similar to the aforementioned programs at that site.