Impact of Injury from Late Season Sequential Glufosinate Applications on Sugarbeet Yield

Experiments were conducted to determine if sugarbeet (Beta vulgaris L.) injury from sequential glufosinate treat" ments starting later than three weeks after the sugarbeet cotyledon stage caused yield loss, and to assess cumulative phytotoxic effects from sequential glufosinate treatments at various rates. Sugarbeet plots were hand weeded until gIufosinate treatments started so that sugarbeet yield loss with late season glufosinate treatments, if any, could be attributed to herbicide injury rather than prolonged early season weed competition. Visible sugarbeet injury was greater when glufosinate treatments were started at three, four, six, or seven weeks after the sugarbeet cotyledon stage rather than one week after the cotyledon stage. The absence of a difference in sugarbeet root yield and extractable sucrose, regardless of glufosinate application starting time, suggests that sugarbeet either partially grew out of the observed leaf chlorosis or that late-appearing visible injury had no adverse effect on yield traits. Regardless of the rate, sugarbeet treated with glufosinate either one or four times had similar root yield and extractable sucrose, which confirms the lack of any signif­ icant cumulative phytotoxic effect on sugarbeet yield from multiple glufosinate applications. Additional Key Words: Beta vulgaris L., weed competition, leaf chlorosis.