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%, 59% 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.