When using glyphosate plus dicamba, 2,4-D, halauxifen or pyraflufen/2,4-D for glyphosate-resistant horseweed (Erigeron canadensis) control in soybean, which third mix partner is better, saflufenacil or metribuzin?

Abstract

Glyphosate-resistant (GR) horseweed interference in soybean can reduce yield up to 93%. Glyphosate plus dicamba, 2,4-D ester, halauxifen-methyl or pyraflufen-ethyl/2,4-D applied preplant (PP) provide variable GR horseweed control in soybean. The objective of the study was to determine if the addition of saflufenacil or metribuzin to glyphosate plus dicamba, 2,4-D ester, halauxifen-methyl or pyraflufen-ethyl/2,4-D will improve the level and consistency of GR horseweed control. Four trials were conducted over the 2020 and 2021 field seasons in fields with GR horseweed populations. Glyphosate plus dicamba, 2,4-D ester, halauxifen-methyl or pyraflufen-ethyl/2,4-D controlled GR horseweed 96, 77, 71, and 52%, respectively at 8 weeks after application (WAA). When saflufenacil or metribuzin was added to glyphosate plus dicamba or 2,4-D ester, GR horseweed control did not improve at 8 WAA. When saflufenacil or metribuzin was added to glyphosate plus halauxifen-methyl, GR horseweed control improved by 27 and 25%, respectively 8 at WAA. When saflufenacil or metribuzin was added to glyphosate plus pyraflufen-ethyl/2,4-D, GR horseweed control was improved by 47 and 37%, respectively at 8 WAA. The consistency of GR horseweed control was improved when saflufenacil or metribuzin was added to glyphosate plus dicamba, 2,4-D ester, halauxifen-methyl or pyraflufen-ethyl/2,4-D compared to each herbicide applied alone. Synergism was observed when metribuzin was added to glyphosate plus halauxifen-methyl and when saflufenacil or metribuzin was added to glyphosate plus pyraflufen-ethyl/2,4-D at 8 WAA. Though GR horseweed control was improved with the addition of saflufenacil or metribuzin to glyphosate plus halauxifen-methyl or pyraflufen-ethyl/2,4-D, all treatments including saflufenacil resulted in the highest level and most consistent control.

Control of glyphosate-resistant horseweed with Group 4 herbicides in soybean

“…Dilliott et al reported additive responses for the control of GR horseweed in soybean when saflufenacil was added to glyphosate þ dicamba. However, the observed plant density and aboveground biomass were greater than expected, indicating an antagonistic interaction (Dilliott et al 2022). The same study reported additive responses when metribuzin was mixed with glyphosate þ dicamba for GR horseweed biomass reduction.…”

“…The same study reported additive responses when metribuzin was mixed with glyphosate þ dicamba for GR horseweed biomass reduction. However, for GR horseweed density, there were antagonistic interactions, as the observed density values were greater than expected (Dilliott et al 2022). Additionally, when saflufenacil was added to glyphosate þ 2,4-D ester, there were additive responses for the control and density and biomass reduction of GR horseweed in soybean (Dilliott et al 2022).…”

“…Additionally, when saflufenacil was added to glyphosate þ 2,4-D ester, there were additive responses for the control and density and biomass reduction of GR horseweed in soybean (Dilliott et al 2022). Dilliott et al (2022) also found synergistic/additive responses when saflufenacil or metribuzin was added to glyphosate þ halauxifen-methyl for the control of GR horseweed in soybean.…”

“…Two-way or three-way mixtures of these herbicides may enhance the effectiveness and uniformity of GR horseweed control in soybean. The use of Group 4 herbicides from different chemical families is suggested not to increase the selection of Group 4-resistant weeds because the herbicides have different binding sites (Dilliott et al 2022). Mixing herbicides may result in synergistic, antagonistic, or additive responses.…”

Tolerance of Dry Beans to Pyraflufen-Ethyl/2,4-D Ester

“…In contrast, Dilliott et al (2022) reported 52% GR Canada fleabane control with pyraflufenethyl/2,4-D applied preplant in soybean. The addition of metribuzin or saflufenacil to pyraflufen-ethyl/2,4-D applied PP improved GR Canada fleabane control to 89% and 99%, respectively (Dilliott et al, 2022).…”