SUGAR-BEET (BETA-VULGARIS) RESPONSE TO AND SORPTION CHARACTERISTICS OF NICOSULFURON AND PRIMISULFURON

Nicosulfuron and primisulfuron are sulfonylurea herbicides that may pe rsist in the soil and injure sensitive rotational crops such as sugarb eet. Studies were initiated to measure sugarbeet response one and two years after application of 70 and 140 g/ha of nicosulfuron and 40 and 80 g/ha of primisulfuron to corn. Nicosulfuron did not injure sugarbee t one or two years after application. In contrast, sugarbeet yield was reduced one year after application of 40 and 80 g/ha of primisulfuron . Injury was visible two years after application of 80 g/ha primisulfu ron but this did not cause a yield reduction. In greenhouse studies, t he concentration of nicosulfuron and primisulfuron that reduced sugarb eet growth by 50% were determined for six soils. Primisulfuron reduced sugarbeet growth more than nicosulfuron on four of six soils indicati ng greater potential for sugarbeet injury from primisulfuron. Sugarbee t response was highly correlated with soil organic matter content (R(2 ) = 0.88). The sorption coefficients, K-d values, for nicosulfuron wer e 0.30 to 2.58 and the K-d values for primisulfuron were 0.76 to 3.47. Primisulfuron K-d values were higher than those of nicosulfuron on fo ur of five soils indicating stronger affinity of primisulfuron for soi l sorptive sites. The K-d values for both herbicides indicate low over all sorption. The greater sugarbeet injury observed in the field from primisulfuron is not due to greater availability of primisulfuron comp ared to nicosulfuron.