Evaluation of Weed Control and Crop Tolerance with Co-application of Glyphosate and Pyraflufen-ethyl in Glyphosate-resistant Soybean (Glycine Max)1

Field trials were conducted to evaluate weed control and soybean tolerance with co-application of pyraflufen-ethyl and glyphosate. Pyraflufen-ethyl applied at 11, 23, or 45 g ai/ha in combination with glyphosate did not affect control of barnyardgrass, browntop millet, redroot pigweed, sicklepod, or smellmelon compared to glyphosate alone or co-applied with chlorimuron. Initial benefit (7 DAT) to pitted morningglory control with pyraflufen-ethyl plus glyphosate compared to glyphosate alone or co-applied with chlorimuron was not observed 28 DAT. Hemp sesbania control was increased by pyraflufen-ethyl at 45 g/ha plus glyphosate and glyphosate plus chlorimuron relative to glyphosate applied alone. Pyraflufen-ethyl plus glyphosate resulted in significant visual soybean injury, and a reduction in soybean yield was observed with pyraflufen-ethyl at 45 g/ha relative to glyphosate applied alone or in combination with chlorimuron. Results from a weed-free study confirmed crop injury and yield reduction potential with pyraflufen-ethyl plus glyphosate. Overall results suggest no benefit with respect to weed control or crop tolerance to pyraflufen-ethyl inclusion in a glyphosate-resistant soybean weed control program over that observed with currently registered co-application of glyphosate and chlorimuron. Nomenclature: Chlorimuron, glyphosate, pyraflufen-ethyl, barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG, browntop millet, Brachiaria ramosa (L.) Stapf. # PANRA, hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX, pitted morningglory, Ipomoea lacunosa L. # IPOLA, redroot pigweed, Amaranthus retroflexus L. # AMARE, sicklepod, Senna obtusifolia L. # SENOB, smellmelon, Cucumis melo L. var. dudaim Naud. # CUMMD, soybean, Glycine max (L.) Merr. Additional index words: Co-application, crop response, crop tolerance, postemergence. Abbreviations: lf, leaf; PDS, post-directed spray; PPO, protoporphyrinogen oxidase.