Date of this Version
De Sanctis JH (2018) Critical period of Palmer amaranth removal and effects of late season herbicide applications on Palmer amaranth seed production. Lincoln, NE: University of Nebraska.
Palmer amaranth is the most troublesome weed in agronomic crops in United States. Therefore, an integrated weed management approach is necessary to successfully manage this weed. The use of residual pre-emergence (PRE) herbicide applied at planting can delays the is one of the critical time of Palmer amaranth removal (CTPAR) giving farmers more time to prepare the weed control tactics and to preventing an unacceptable yield loss in soybean due to Palmer amaranth competition. Field experiments were conducted in 2018 and 2019 in a grower’s field infested with GR Palmer amaranth near Carleton, Nebraska, to determine the CTPAR in soybean affected by residual pre-emergence (PRE) herbicides compared with the no PRE herbicide in southcentral Nebraska. Results demonstrated that ). In absence of a PRE herbicide, the CTPAR at 5% soybean yield loss occurred at V1 and V6 soybean growth stages, in 2018 and 2019, respectively. When flumioxazin was applied alone, the CTPAR was delayed until V3 and V6 soybean growth stages compared with V2 and R1 soybean growth stages when the flumioxazin/metribuzin/pyroxasulfone premix was applied, in 2018 and 2019, respectively.
Late-emerged Palmer amaranth plants and plants that survived POST applications are usually ignored by weed management programs based on yield loss once they normally do not cause an unacceptable yield loss. However, those plants can grow and produce seed, thus, replenishing the soil seedbank and increasing the chances for evolution of herbicide-resistant biotypes. Field experiments were conducted in a grower’s field infested with GR Palmer amaranth near Carleton, NE, in 2018 and 2019 to evaluate the effects of single or sequential late season applications of labeled POST herbicides such as acifluorfen, dicamba, fomesafen/fluthiacet-methyl, glyphosate, and lactofen on GR Palmer amaranth control, density, biomass, seed production, and fecundity as well as grain yield of dicamba/glyphosate-resistant (DGR) soybean. Dicamba applied at V4 soybean growth stage (SGS) or in sequential applications at V4 followed by R1 or R3 SGS provided 86% to 97% control, reduced Palmer amaranth seed production in the range of 557 to 2,911 seeds per female plant and secured the highest soybean yield during both years of the study.
Advisor: Amit J. Jhala