Evaluation of herbicide programs in acetolactate synthase-resistant grain sorghum

Abstract

The acetolactate synthase inhibitor herbicide-resistant grain sorghum technology introduced will allow for the application of nicosulfuron for postemergence (POST) grass control, however it is essential to determine a program-based approach to ensure broad spectrum weed control. Field experiments were conducted at three locations across Kansas in 2015 and 2016 to assess a range of possible herbicide programs for grass and broadleaf weed control and crop tolerance using Inzen™ Sorghum. The experiments consisted of 1 early pre-plant (EPP), 2 preemergence (PRE), and 3 POST, and 5 PRE followed by POST herbicide treatments. Weed control and crop response were evaluated visually at 1, 2, and 4 weeks after POST treatment (WAPT). Treatments containing nicosulfuron and/or bromoxynil & pyrasulfotole caused 10 to 20% crop injury at 1 WAPT in both 2015 and 2016 at the three locations. Treatments containing nicosulfuron + dicamba caused up to 30% injury with more injury in 2015 than in 2016. In 2015 at Manhattan the nicosulfuron-only treatment provided 64% control of Palmer amaranth and, when tank mixed with dicamba or bromoxynil & pyrasulfotole, control ranged from 71 to 76%. When nicosulfuron POST followed PRE of S-metolachlor & atrazine, Palmer amaranth control was 96 to 100%. At both locations, nicosulfuron provided 35, 55, and 61% control of large crabgrass, yellow foxtail, and stinkgrass, respectively. Annual grass control ranged from 85 to 100% when nicosulfuron followed a PRE S-metolachlor & atrazine. Greenhouse experiments were set up to determine the efficacy of nicosulfuron on four annual grass species at six different rates, two different rates, and the addition of atrazine. The four grass species evaluated were large crabgrass, yellow foxtail, barnyardgrass, and wheat. Nicosulfuron was applied at 0.125, 0.25, 0.5, 1, 2 times its labeled rate of 35 g ha⁻¹. A full factorial of rate by height by atrazine was applied for a total of 24 treatments replicated 4 times on each species. Each nicosulfuron rate was applied with and without atrazine at 840 g ha⁻¹ on 5 to 10 cm tall plants and on 15 to 20 cm tall plants. Visual ratings were taken 1, 2, and 4 weeks after treatment (WAT). Aboveground biomass was harvested 4 WAT, dried and weighed. Treatments containing nicosulfuron from 4.4 to 70 g ha⁻¹ all caused similar reduction in biomass compared to the nontreated check. Averaged over the inclusion of atrazine, nicosulfuron applied at 35 and 70 g ha⁻¹ provided 17% less control when treating 15 to 20 cm large crabgrass compared to the 5 to 10 cm large crabgrass, respectively. Overall barnyardgrass, yellow foxtail, and wheat can be effectively controlled with nicosulfuron when applied at proper heights, rate, and atrazine.