Palmer Amaranth (Amaranthus palmeri) and Velvetleaf (Abutilon theophrasti) Control in No-Tillage Conventional (Non-genetically engineered) Soybean Using Overlapping Residual Herbicide Programs

Due to depressed corn and soybean prices over the last few years in the United States, growers in Nebraska are showing interest in no-tillage (hereafter referred to as no-till) conventional (non-genetically engineered [non-GE]) soybean production. Due to the increasing number of herbicide-resistant weeds in the United States, weed control in no-till non-GE soybean using POST herbicides is a challenge. The objectives of this study were to compare PRE-only, PRE followed by (fb) POST, and PRE fb POST with residual (POST-WR) herbicide programs for Palmer amaranth and velvetleaf control and soybean injury and yield, as well as to estimate the gross profit margins and benefit-cost ratio of herbicide programs. A field experiment was conducted in 2016 and 2017 at Clay Center, NE. The PRE herbicides tested in this study resulted in >= 95% Palmer amaranth and velvetleaf control at 28 d after PRE (DAPRE). Averaged across the programs, the PRE-only program controlled Palmer amaranth 66%, whereas 86% and 97% control was obtained with the PRE fb POST and PRE fb POST-WR programs, respectively, at 28 d after POST (DAPOST). At 28 DAPOST, the PRE fb POST herbicide programs controlled velvetleaf 94%, whereas the PRE-only program resulted in 85% control. Mixing soil-residual herbicides with foliar-active POST programs did not improve velvetleaf control. Averaged across herbicide programs, PRE fb POST programs increased soybean yield by 10% and 41% in 2016 and 2017, respectively, over the PRE-only programs. Moreover, PRE fb POST-WR programs produced 7% and 40% higher soybean yield in 2016 and 2017, respectively, compared with the PRE fb POST programs. The gross profit margin (US$1,184.3 ha(-1)) was highest under flumioxazin/pyroxasulfone (PRE) fb fluthiacet-methyl plus S-metolachlor/fomesafen (POST-WR) treatment; however, the benefit-cost ratio was highest (6.1) with the PRE-only program of flumioxazin/chlorimuron-ethyl.