Abstract
Glyphosate + dicamba has provided variable glyphosate-resistant Canada fleabane (GRCF) control in glyphosate/dicamba-resistant (GDR) soybean. Previous research has indicated improved GRCF control when a third herbicide was added to glyphosate + dicamba, though research is limited. The objective of this research was to ascertain if the level and consistency of GRCF control can be improved when adding tiafenacil, metribuzin, bromoxynil, pyraflufen-ethyl/2,4-D, 2,4-D ester, halauxifen-methyl or saflufenacil to glyphosate + dicamba applied preplant (PP) in GDR soybean. Four field trials were conducted in 2020 and 2021 in commercial fields in southwestern Ontario, Canada. Glyphosate + dicamba controlled GRCF 57, 93 and 94% at 2, 4 and 8 WAA, respectively. Adding bromoxynil to glyphosate + dicamba improved GRCF control from 57 to 77% at 2 WAA; adding saflufenacil to glyphosate + dicamba improved GRCF control from 57 to 92, 93 to 99, and 94 to 99% at 2, 4 and 8 WAA, respectively. All three-way tank-mixtures improved the consistency of GRCF control, except for glyphosate + dicamba + 2,4-D ester at 2 WAA, glyphosate + dicamba + 2,4-D ester, tiafenacil or metribuzin at 4 WAA, and glyphosate + dicamba + tiafenacil or bromoxynil at 8 WAA. This study concludes that the level and consistency of GRCF control was improved when saflufenacil was added to a PP application of glyphosate + dicamba in soybean.
Highlights
Canada fleabane (Erigeron canadensis L.) is a problematic weed from the Asteraceae family [1,2]
It was difficult to detect differences when adding a third herbicide to glyphosate + dicamba since glyphosate + dicamba provided a high level of glyphosate-resistant Canada fleabane (GRCF) control at 4 and 8 weeks after application (WAA)
Though glyphosate + dicamba provided a high level of GRCF control at 4 and 8 WAA, adding saflufenacil to glyphosate + dicamba improved control from 57 to 92, 93 to 99, and to 99% at 2, 4 and 8 WAA, respectively
Summary
Canada fleabane (Erigeron canadensis L.) is a problematic weed from the Asteraceae family [1,2]. It emerges primarily in the spring from April to June, and in the fall from September to October [3,4]. Biotypes can germinate at low temperatures of 8 ◦ C [5] and have been reported to germinate 11 months of the year excluding January [3,4]. Fall-emerged Canada fleabane overwinters as a rosette, which gives it a competitive edge over spring-seeded annual crops and later-emerging weeds [4,6]. Canada fleabane is highly prolific, with individual plants producing thousands of seeds [7,8]; fecundity is correlated with plant height [1,9,10]. The seeds have a feather-like structure attached—known as the pappus—
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