Control of glyphosate-resistant horseweed and giant ragweed in soybean with halauxifen-methyl applied preplant

Abstract

Horseweed and giant ragweed are competitive, annual weeds that can negatively impact crop yield. Biotypes of glyphosate-resistant (GR) giant ragweed and horseweed were first reported in 2008 and 2010 in Ontario, respectively. GR horseweed has spread throughout the southern portion of the province. The presence of GR biotypes poses new challenges for soybean producers in Canada and the United States. Halauxifen-methyl is a recently registered selective herbicide for broadleaf weeds, for preplant use in corn and soybean. There is limited literature on the efficacy of halauxifen-methyl on GR horseweed and giant ragweed when combined with currently registered products in Canada. The purpose of the experiment was to determine the effectiveness of halauxifen-methyl applied alone, and tank-mixed for GR giant ragweed and GR horseweed control in glyphosate and dicamba-resistant (GDR) soybean in southwestern Ontario. Six field experiments were conducted separately for each weed species over 2018 and 2019. Halauxifen-methyl applied alone controlled GR horseweed 72% at 8 weeks after application (WAA). Control was improved to >91% when halauxifen-methyl applied in combination with metribuzin, saflufenacil, chlorimuron-ethyl + metribuzin and saflufenacil + metribuzin. At 8 WAA, halauxifen-methyl controlled GR giant ragweed 11%; glyphosate/2,4-D choline, glyphosate/dicamba, glyphosate/2,4-D choline + halauxifen-methyl and glyphosate/dicamba + halauxifen-methyl controlled GR giant ragweed 76 to 88%. This study concluded that halauxifen-methyl applied preplant in a tank-mixture can provide effective control of GR giant ragweed and horseweed in GDR soybean.

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?

“…When metribuzin was added to glyphosate plus halauxifen-methyl, GR horseweed control improved by 43%, 31%, and 25% at 2, 4, and 8 WAA, respectively, and decreased density and biomass 94% and 86%, respectively. Similar results were reported by Quinn et al (2021), who observed 93% GR horseweed control in soybean at 8 WAA and a 98% and 99% reduction in density and biomass, respectively, with glyphosate (900 g ae ha -1 ) plus halauxifenmethyl (5 g ai ha -1 ) plus metribuzin (400 g ai ha -1 ). Based on Colby's equation, the improvement in GR horseweed control 2, 4, and 8 WAA and the decrease in density and biomass was synergistic when metribuzin was added to glyphosate plus halauxifen-methyl (Equations 1 and 2).…”

“…In the present study, when saflufenacil was added to glyphosate plus halauxifen-methyl, GR horseweed control improved by 57%, 36%, and 27% at 2, 4, and 8 WAA, respectively, and decreased GR horseweed density and biomass by 95% and 92%, respectively (Table 6). Similarly, Quinn et al (2021) observed 91% GR horseweed control using glyphosate (900 g ae ha -1 ) plus halauxifen-methyl (5 g ai ha -1 ) plus saflufenacil (25 g ai ha -1 ) when applied PP in soybean at 8 WAA and a 97% and 98% decrease in density and biomass, respectively. Based on Colby's equation, the addition of saflufenacil to glyphosate plus halauxifen-methyl was additive for control 4 and 8 WAA and synergistic at 2 WAA; the interaction for density and biomass reduction was additive (Equations 1 and 2).…”

Improving the Level and Consistency of Glyphosate-Resistant Canada Fleabane (Erigeron canadensis L.) Control With Bromoxynil-Based Tankmixes Applied Preplant to Soybean

“…Glyphosate plus halauxifen-methyl or dicamba reduced GR Canada fleabane biomass 92 and 97%, respectively; biomass was not reduced with glyphosate plus metribuzin, tiafenacil, pyraflufen-ethyl/2,4-D, 2,4-D ester or saflufenacil. Similar reductions in GR Canada fleabane biomass have been reported in past research (Budd et al, 2016;Byker et al, 2013a;Quinn et al, 2021). When bromoxynil was added to glyphosate plus metribuzin GR Canada fleabane biomass was reduced by 18%; interestingly, there was no benefit of adding bromoxynil to glyphosate plus tiafenacil, pyraflufen-ethyl/2,4-D, 2,4-D ester, halauxifen-methyl, saflufenacil or dicamba in respect to Canada fleabane biomass.…”

“…Mahoney et al (2017) and Metzger et al (2019) observed 93 and 94% control, respectively of GR and multiple-herbicide-resistant (MHR) Canada fleabane with bromoxynil (280 g ai ha -1 ) plus atrazine (1500 g ai ha -1 ) applied POST in corn 8 WAA. Quinn et al (2021) reported 98% GR Canada fleabane control with a premix of pyrasulfotole/bromoxynil (205 g ai ha -1 ) plus AMS (1 L ha -1 ) applied POST in winter wheat 8 WAA. Mahoney et al (2016) observed bromoxynil (174 g ai ha -1 ) plus pyrasulfotole (31 g ai ha -1 ) applied POST controlled 97% of GR Canada fleabane in winter wheat at 8 WAA.…”

Strategies to improve the control of glyphosate-resistant horseweed (Erigeron canadensis) with glufosinate applied preplant to soybean

“…Eubank et al (2008) reported soybean yields comparable to the present study with glufosinate-based mixtures. In contrast, Quinn et al (2021) reported that interference from GR horseweed reduced soybean yield in the weedy control by 1500 kg ha -1 relative to the weed-free control.…”