Effect of glufosinate rate and addition of ammonium sulfate on annual weed control in glyphosate/glufosinate/2,4-D–resistant soybean

Abstract The development of glufosinate-resistant soybean cultivars has created opportunities for use of glufosinate applied postemergence for weed control. Four field experiments were conducted in 2021 and 2022 to ascertain the effect of glufosinate rate and the addition of ammonium sulfate on annual weed control in glyphosate/glufosinate/2,4-D–resistant soybean. An increased glufosinate rate of 500 from 300 g ai ha–1 improved control of common ragweed, common lambsquarters, redroot pigweed, and foxtail species and resulted in decreased density and dry biomass of common lambsquarters and foxtail species. The addition of ammonium sulfate to glufosinate increased control of common lambsquarters, 2 and 8 wk after application (WAA), and of foxtail species, 2, 4, and 8 WAA, but did not improve control of common ragweed and redroot pigweed. Increasing the dose of glufosinate from 300 to 500 g ai ha–1 improves control of common ragweed, redroot pigweed, common lambsquarters, and foxtail species; however, the benefit of the addition of ammonium sulfate to glufosinate is weed species-specific. Nomenclature: Glyphosate; glufosinate; common ragweed; Ambrosia artemisiifolia L.; common lambsquarters; Chenopodium album L.; green foxtail; Seteria viridis (L.) P. Beauv.; velvetleaf; Abutilon theophrasti Medik.; soybean; Glycine max (L.) Merr.