Weed Control and Glyphosate-tolerant Sugarbeet Response to Herbicide Treatments

Field experiments were conducted in 1998 and 1999 at two Wyoming locations, Powell and Torrington Research and Extension Centers, to evaluate weed control efficacy and glyphosate-tolerant sugarbeet response to glyphosate alone and in combination with residual herbicides. Weed control with a single glyphosate application was inadequate for all species except wild mustard. Two sequential applications starting at 2-, 4-, and 6-leaf sugarbeet with a two week interval between applications provided more than 90% weed control. Similar weed control was provided with three applications starting at 2- or 4-leaf sugarbeet with one or two week intervals between applications, respective­ ly. Residual herbicides followed by one or two applications of' glyphosate starting at 4-leaf sugarbeet provided excel­ lent weed control. No sugarbeet injury was recorded with glyphosate alone. However, sugarbeet injury with treat­ ments containing residual herbicides ranged from 0 to 10%. With glyphosate alone, sugarbeet root yield increased as the number and frequency of applications increased. Highest yields were obtained with two or three applications of glyphosate starting at 2- or 4-leaf sugarbeet. Similar yields were obtained with residual herbicides in combina­ tion with one or two applications of glyphosate starting at 4-leaf sugarbeet. None of the treatments, including the weedy check, affected sucrose content. Sucrose yield dif­ fered among treatments and corresponded to sugarbeet root yield. Additional Key Words: Ethofumesate, desmedipham, phenmedipham,