DEGRADATION OF PRIMISULFURON-METHYL AND METSULFURON-METHYL IN SOIL

A newly developed chemical assay was used to determine the degradation in soil of two sulfonylurea herbicides, primisulfuron-methyl and mets ulfuron-methyl, under both controlled and field conditions. The result s from the chemical assay were compared with those from traditional bi oassays for determination of persistence in the field. Phytotoxic effe cts of these herbicides were not observed after 6 weeks following appl ication to an acidic (pH 5 . 7) soil with high organic matter content (7 . 3% o.c.). Half-lives of 13 to 29 days were measured for primisulf uron-methyl at different soil-water contents and temperatures while th ose for metsulfuron-methyl ranged from 8 to 36 days. The rate of degra dation of metsulfuron-methyl was more sensitive to temperature than th at of primisulfuron-methyl. Persistence in the field was shorter than expected considering the results from the controlled environment studi es. However, determination of the persistence by both chemical assay a nd bioassay methods produced very similar results.