Glyphosate-Resistant Canada Fleabane Control with Three-Way Herbicide Tankmixes in Soybean

Abstract

Eight field trials ( 2 in 2016, 3 in 2017, 3 in 2018) were conducted in farmers’ fields with heavy infestations of GR Conyza canadensis (Canada fleabane, horseweed or marestail ) to evaluate glyphosate (900 g ae ha -1 ) plus saflufenacil (25 g ai ha -1 ), 2,4-D ester (500 g ai ha -1 ) or paraquat (1100 g ai ha -1 ) applied preplant (PP) as 2-way tankmixes , or in 3-way tankmixes with sulfentrazone (140 g ai ha -1 ), flumioxazin (107 g ai ha -1 ) or metribuzin (400 g ai ha -1 ) for the glyphosate-resistant (GR) C. canadensis control in GR soybean. Glyphosate plus saflufenacil applied PP controlled GR C. canadensis as much as 90%. The addition of sulfentrazone, flumioxazin or metribuzin to the tankmix provided as much as 93%, 96% and 97% control of GR C. canadensis , respectively. Glyphosate plus 2,4-D ester applied PP provided as much as 59% control of GR C. canadensis . The addition of sulfentrazone, flumioxazin or metribuzin to the tankmix provided as much as 60%, 5 9% and 91% control of GR C. canadensis , respectively. Glyphosate plus paraquat applied PP provided as much as 85% control of GR C. canadensis . The addition of sulfentrazone, flumioxazin or metribuzin to the tankmix provided as much as 88%, 89% and 98% control of GR C. canadensis , respectively. Density and biomass reductions of GR C. canadensis with herbicides evaluated followed the same pattern as weed control evaluations. GR C. canadensis interference reduced soybean yield 66%. Reduced GR C. canadensis interference with the preplant herbicides evaluated provided soybean yield similar to the weed-free control. Results from this study show that glyphosate plus saflufenacil , glyphosate plus 2,4-D ester or glyphosate plus paraquat tankmixed with metribuzin can provide effective control of GR C. canadensis in GR soybean.