Pre‐plant and in‐crop herbicide programs for prickly sida control in soybean

Abstract

AbstractPrickly sida (Sida spinosa L.) is emerging as a prevalent and troublesome weed in the Mid‐South glyphosate‐resistant (GR) soybean [Glycine max (L.) Merr.] cropping systems as reliance on residual herbicides has decreased. It emerges throughout the growing season and postemergence (POST) control has been reported to be variable. Combinations of residual herbicides applied pre‐plant and at‐planting followed by POST herbicides in‐crop may be needed to maximize control. This research utilized separate studies to address the value of currently available residual herbicides applied pre‐plant, at‐planting, and POST in glyphosate‐resistant soybean prickly sida management systems. At 35 days after application (DAA), prickly sida control from glyphosate plus 2,4‐D pre‐plant with flumioxazin plus chlorimuron‐ethyl, flumioxazin plus pyroxasulfone, flumioxazin plus chlorimuron‐ethyl plus thifensulfuron‐methyl, metribuzin plus chlorimuron‐ethyl or metribuzin plus sulfentrazone was 70–89% and similar among treatments. In a separate study, based on prickly sida control and density 21 days after late postemergence (LPOST) application, improvement in control was most affected by inclusion of glyphosate or glyphosate plus residual herbicides flumioxazin, chlorimuron‐ethyl, and thifensulfuron‐methyl at‐planting. Weed control was not improved when residual herbicides chlorimuron‐ethyl plus tribenuron‐methyl were included pre‐plant or when residual herbicides chlorimuron‐ethyl, s‐metolachlor, and fomesafen were applied with glyphosate POST. Late‐season prickly sida control was as high as 93% following at‐planting and POST applications that did not include residual herbicides. Soybean yield was maximized with glyphosate applied both at‐planting and POST, whether or not residual herbicides flumioxazin, chlorimuron‐ethyl, and thifensulfuron‐methyl were included at‐planting or residual herbicides chlorimuron‐ethyl, s‐metolachlor, or fomesafen were included POST. When averaged across at‐planting and POST treatments, a 10% yield increase was observed when residual herbicides chlorimuron‐ethyl and tribenuron‐methyl were applied with glyphosate plus 2,4‐D pre‐plant compared with glyphosate plus 2,4‐D alone.