Control of glyphosate-resistant waterhemp ( Amaranthus tuberculatus ) in dicamba - resistant soybean in New York

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Abstract
Recent reports of glyphosate-resistant (GR) waterhemp pose serious concerns among crop producers in New York. Field experiments were conducted in 2019 and 2020 near Waterloo, New York, to evaluate the effectiveness of preemergence, postemergence, preemergence followed by (fb) postemergence, and preemergence herbicides fb row cultivation (RC) to control glyphosate-resistant (GR) waterhemp in dicamba-resistant (DR) soybean. In 2019, all two-pass herbicide treatments resulted in significantly reduced GR waterhemp densities (2 to 13 plants m −2 ) compared with nontreated plots (160 plant m −2 ) at 8 wk after preemergence/2 wk after postemergence, reductions in shoot dry biomass (85% to 99% of nontreated), and greater soybean grain yields (2,659 to 2,936 kg ha −1 ). In addition, flumioxazin, acetochlor, chlorimuron + flumioxazin + metribuzin, acetochlor + fomesafen + metribuzin, carfentrazone + sulfentrazone + metribuzin, and S -metolachlor + sulfentrazone + metribuzin applied preemergence resulted in significant reductions in GR waterhemp density (3 to 19 plants m −2 ) and shoot dry biomass (60% to 98% of nontreated). In 2020, most preemergence (except cloransulam), postemergence only, and preemergence fb postemergence herbicide application strategies resulted in lower densities of GR waterhemp (1 to 46 plants m −2 ) compared with nontreated plots (104 plants m −2 ) at 8 wk after preemergence/2wk after postemergence and lower shoot dry biomass (66% to 99% of nontreated). All two-pass strategies as well as metribuzin, acetochlor + fomesafen + metribuzin, carfentrazone + sulfentrazone applied preemergence resulted in higher grain yields (3,343 to 4,244 kg ha −1 ). These results conclude that two-pass strategies tested in this research can consistently provide effective control of GR waterhemp in DR soybean in New York.

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