Yield of Glufosinate-Resistant Sugarbeet in Response to Postemergence Glufosinate

ha· Experiments were conducted to determine the effect of glu­ fosmate rate and herbicide starting time on glufosinate­ resistant sugarbeet (Beta vulgaris L) injury and yield. Sequential glnfosinate applications starting two weeks or later and ending five to seven weeks after the sugarbeet cotyledon stage caused significant visible sugarbeet injury while injury was minimal with treatments starting at the cotyledon stage or one week later. Sugarbeet yield declined when sequential glufosinate treatments were applied at weekly intervals and the first treatment was delayed until f~ur weeks or one week after the sugarbeet cotyledon stage in 1998 and 1999, respectively. Sugarbeet yield loss may be attributed to sugarbeet injury or prolonged weed competi­ tion prior to the first sequential glufosinate application. As the glufosinate rate increased from 0.2 to 0.4 and 0.8 kg l , glufosinate had to be applied to younger sugarbeet to a-void sugarbeet injury. Glufosinate-resistant sugarbeet treat-ed three times with glufosinate yielded less in 1998 than sugarbeet that was hand weeded at the same time pat­ tern as glufosinate was applied. Similar results were found in 1999 at one location, but yield from glufosinate-treated and hand-weeded plots did not differ at two locations, despite the significant herbicide­ induced sugarbeet injury observed seven days after the last treatment. Glufosinate, regardless of rate, can safely be applied to sugarbeet starting at the cotyledon stage or one week thereafter without causing yield loss.