NICOSULFURON AND PRIMISULFURON ROOT UPTAKE, TRANSLOCATION, AND INHIBITION OF ACETOLACTATE SYNTHASE IN SUGAR-BEET (BETA-VULGARIS)

Field studies have shown primisulfuron to be more injurious to sugarbe et than nicosulfuron 1 and 2 yr after herbicide application. Experimen ts were initiated to determine if primisulfuron is more injurious to s ugarbeet grown in a nutrient culture and if the difference in sugarbee t response is a result of greater uptake, translocation, or acetolacta te synthase (ALS) site sensitivity with primisulfuron. Concentrations of primisulfuron and nicosulfuron that reduced sugarbeet growth by 50% were 1.9 and 8.9 mu g ai L(-1), respectively, at pH 6.5. The pH of th e nutrient solution did not influence sugarbeet response to either her bicide. Uptake of primisulfuron was greater (3%) than that of nicosulf uron (1%). Translocation (expressed as a percent of uptake) of nicosul furon was more rapid than primisulfuron. Fifty-seven percent of the ab sorbed nicosulfuron translocated out of the root during the 12-h pulse period, while an equal concentration of primisulfuron was not translo cated out of the root until 48 h after pulsing. The total nicosulfuron translocated after 144 h was half that of primisulfuron. The nutrient solution taken up by sugarbeet in the 12-h pulse period was reduced b y 41% in the presence of either herbicide compared to the untreated co ntrol. The ALS enzyme was a minimum of 15 times more sensitive to prim isulfuron compared to nicosulfuron which may account for greater sugar beet response to primisulfuron.