What antagonistic interactions mean for Enlist and Roundup Ready Xtend technologies

Abstract

AbstractThe commercialization of Roundup Ready Xtend and Enlist cropping systems increased the number of herbicide products available for postemergence application in soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum L.). A greater understanding of how glyphosate, glufosinate, dicamba, and 2,4‐D interact in mixture is needed. Two field experiments were conducted in 2015 and 2016 at the Northeast Research and Extension Center in Keiser, AR, to evaluate herbicide interactions that could occur in Enlist and Roundup Ready Xtend cropping systems. Various rates and combinations of glufosinate, glyphosate, dicamba, and 2,4‐D were applied and evaluated for percent weed control 5 wk after treatment (WAT). In the 2,4‐D experiment, glyphosate (dimethylamine salt) at 0.75 lb ae ac−1 provided 88% barnyardgrass [Echinochloa crus‐galli (L.) Beauv.] control, whereas a premixture of glyphosate at 0.75 lb ae ac−1 + 2,4‐D at 0.70 lb ae ac−1 provided 80% control 5 WAT. Similarly, in the dicamba experiment, glyphosate (potassium salt) at 0.77 lb ae ac−1 provided 86% barnyardgrass control, compared to 79% with glyphosate at 0.77 lb ae ac−1 + dicamba at 0.5 lb ae ac−1. Antagonism was also identified for mixtures of glufosinate + glyphosate for barnyardgrass in both experiments. For Palmer amaranth (Amaranthus palmeri, S. Wats) and prickly sida [Sida spinosa (L.)] control, mixtures were generally equal to or greater than the individual herbicides alone, even though some mixtures were deemed antagonistic. Herbicide applicators in Roundup Ready Xtend or Enlist systems should be aware of antagonistic interactions and the implications of antagonism on herbicide resistance management.