PERSISTENCE AND MOBILITY OF CHLORSULFURON AND METSULFURON UNDER DIFFERENT SOIL AND CLIMATIC CONDITIONS

The persistence and mobility of chlorsulfuron and metsulfuron were stu died in Italy at four field locations. Chlorsulfuron was applied pre-e mergence to wheat at 15 and 30 g a.i. ha-1 in the autumn of 1986 and m etsulfuron early post-emergence at 8 g a.i. ha-1 in the spring of 1987 . Soil samples were taken periodically at each location for 1 year. Tr ials were conducted until 1989 at three locations. After the wheat har vest in 1989, chlorsulfuron and metsulfuron residues in the soil were measured by bioassay in plots that had been treated annually for 3 yea rs and also in plots that had received single treatments. Chlorsulfuro n at both application rates dissipated to levels below 0.3 g a.i. ha-1 over 12 months at three locations while, at the fourth, which receive d only 250 mm rain during the study, significant levels of residues we re still present after 15 months. The degradation of chlorsulfuron app lied at 30 g a.i. ha-1 followed first-order kinetics, with half-lives of 149, 70, 59 and 51 days at the four locations. Chlorsulfuron mobili ty was high at three locations while, in the silty clay soil of the fo urth, the herbicide was confined to the upper 30 cm, despite the high rainfall. Metsulfuron applied in spring was detected only in the first soil sample collection. It was present in all sampled layers at one l ocation but, in the others, was confined to the surface layer. There w as no evidence of herbicide accumulation in the soil with repeated app lications.