Response of sugarbeet, common sunflower, and common cocklebur to clopyralid or desmidipham plus phenmedipham

A three-year experiment was conducted near Scottsbluff, NE, to evaluate the selectivity of clopyralid, desmedipham plus phenmedipham, and the combination for common sunflower and common cocklebur control in sugarbeet. Clopyralid provided 81 to 98% control of common sunflower and 95 to 98% control of common cocklebur while desmedipham plus phenmedipham provided poor control of both weeds. Combinations of clopyralid plus desmedipham plus phenmedipham provided good control of both weeds but in some years the treatment increased sugarbeet injury over that observed when clopyralid was applied alone. Common sunflower and common cocklebur at densities of 5 plants/9 m of crop row reduced sugarbeet root yield 31 and 28%, respectively. Clopyralid's efficacy on common sunflower and common cocklebur was reflected in sugarbeet root yields similar to those observed in a handweeded control.