In-season applications of glyphosate for control of redvine (Brunnichia ovata) in glyphosate-resistant soybean

An experiment was initiated at two sites in 1998 near Crowder, MS, to evaluate the effect of in-season applications of glyphosate on redvine populations in glyphosate-resistant soybean. In the year of application, most treatments containing multiple in-season applications of glyphosate reduced redvine populations. However, at 16 mo after treatment (October 1999), 0.63 kg ai/ha paraquat preplant followed by sequential postemergence applications of glyphosate at 1.1 and 2.2 kg ai/ha reduced redvine stems by 45% compared with the untreated check. Redvine control with this treatment also was comparable with 2.2 kg ai/ha dicamba preharvest. The same results were observed at 12 and 14 mo after application with many treatments containing sequential applications of glyphosate, but glyphosate at 1.1 and 2.2 kg ai/ha was the only in-season treatment to maintain redvine suppression during the entire growing season the year after herbicide application. However, a number of treatments delayed redvine reinfestation; thus, soybean yield was improved over the untreated check with all treatments from the previous year containing in-season applications of glyphosate, except for 0.84 kg/ha followed by 0.56 kg/ha. Increasing rates of in-season glyphosate applications to 1.1 followed by 2.2 kg/ha will adequately suppress redvine populations in glyphosate-resistant soybean, controlling annual weeds in the process.