Sensitivity of pearl millet parental lines to POST herbicides: Clethodim, quizalofop-p-ethyl, imazamox, and nicosulfuron

Pearl millet is a climate-resilient grain and forage crop. Weeds pose a major constraint to its successful production. Limited herbicide options for grass weed control in pearl millet is a serious problem. The objectives of this study were (1) to evaluate the sensitivity of pearl millet parental lines to POST-applied clethodim (136 g ai ha-1), quizalofop-p-ethyl (QPE) (77 ai g ha-1), imazamox (52 g ai ha-1), and nicosulfuron (70 g ai ha-1) and (2) to characterize the sensitivity of selected lines to imazamox and nicosulfuron. A total of 56 parental lines were tested. Three lines with low sensitivity to imazamox (ARCH35R, 45R, and 73R), two to nicosulfuron (ARCH45R and 73R), one line with high sensitivity (ARCH21B), and a susceptible sorghum (SOR) hybrid (P84G62) to both herbicides were characterized. All parental lines were sensitive to clethodim and QPE (only four lines showed 2% to 12% survival with 90% to 95% injury at 21 d after application [DAA]). However, all parental lines showed variable sensitivity to imazamox and nicosulfuron (70% to 100% survival with 5% to 70% visible injury and shoot dry biomass reduction at 21 DAA). Dose-response assays revealed that ARCH35R, 45R, and 49R had 7.7- to 12.2-fold and 3.2- to 12.2-fold reduced sensitivity to imazamox compared to ARCH21B and SOR, respectively. Similarly, ARCH45R and 49R had 2.5- to 6.0-fold and 1.5- to 3.7-fold reduced sensitivity to nicosulfuron compared to ARCH21B and SOR, respectively. These findings confirm the first report of reduced sensitivity to imazamox and nicosulfuron among pearl millet lines, suggesting their potential use for in-season grass weed control.