Biological effects on Palmer amaranth surviving glufosinate

Abstract

Palmer amaranth (Amaranthus palmeri S. Watson) is a difficult weed to manage due to competitive growth, fecundity, and evolved herbicide resistance. Limited information exist on the fecundity of vegetative stage Palmer amaranth surviving glufosinate applied at different timings. In addition, research has not investigated the germination or glufosinate susceptibility of the offspring from these surviving plants. Field experiments were conducted across three locations in 2019 to determine (a) the fecundity of Palmer amaranth plants surviving glufosinate applied at different vegetative growth stages, and (b) if the offspring from the surviving plants exhibited differential germination and susceptibility to glufosinate. Palmer amaranth was treated at three different vegetative sizes (5 cm, 7-10 cm, > 10 cm) and orthogonal combinations of these application timings. The application timings corresponded to early-, mid-and late-postemergence applications. Palmer amaranth plants surviving the mid-, late-, and the mid postemergence followed by late postemergence glufosinate application were fecund. Palmer amaranth plants surviving the mid postemergence followed by late postemergence application produced less seed than the plants surviving the mid postemergence and late postemergence application. Palmer amaranth was controlled with other glufosinate applications resulting in no seed production. Germination was affected across location and glufosinate treatments, but no clear trend/pattern was observed. The offspring from Palmer amaranth plants surviving glufosinate applications were controlled by all glufosinate rates tested. These experiments provide evidence that Palmer amaranth surviving glufosinate in the vegetative stages may remain fecund, but fecundity can vary with application timing. No measurable effect on the offspring germination or susceptibility to glufosinate was apparent.

Confirmation and inheritance of glufosinate resistance in an Amaranthus palmeri population from North Carolina

“…This result suggests that the Anson County population is consistently surviving lethal glufosinate rates similarly to previously confirmed glufosinate‐resistant A. palmeri populations. The LD 50 of the Anson County population in the glasshouse is a historically efficacious rate in the field on similar sized Amaranthus plants, which further demonstrates that herbicide susceptibility within a genus/species can change spatially and temporally (Beyers et al., 2002 ; Corbett et al., 2004 ; Culpepper et al., 2000 ; Jones, Leon, & Everman, 2022 ). The difference in LD 50 for the Anson County population may be exaggerated if compared to historic accessions as herbicide susceptibility can change spatially and temporally (Heap, personal communication) (Mahoney et al., 2020 ; Owen et al., 2014 ).…”

Late postemergence glufosinate‐based programs for glyphosate‐resistant Palmer amaranth control in dicamba/glufosinate/glyphosate‐resistant soybean

“…• Single (655 or 737 g ha −1 ) and all sequential late-POST glufosinate programs provided 87%-93% control of GR Palmer amaranth. (Jones et al, 2022;Meyer et al, 2015). However, the cut-off dates for POST dicamba applications on DGG-resistant soybean vary from state to state according to recent changes approved by the EPA.…”

“…Dicamba/glufosinate/glyphosate (DGG)‐resistant soybean (XtendFlex, Bayer CropScience) was commercially launched in 2021 in the United States and Canada. The adoption of DGG‐resistant soybean allows growers to use single or sequential applications of low‐volatile dicamba formulations and glufosinate for in‐season control of GR weeds such as waterhemp ( Amaranthus tuberculatus L.) and Palmer amaranth (Jones et al., 2022; Meyer et al., 2015). However, the cut‐off dates for POST dicamba applications on DGG‐resistant soybean vary from state to state according to recent changes approved by the EPA.…”