Transport of thifensulfuron-methyl and tribenuron-methyl in runoff

Excerpt

Sulfonylurea herbicides are highly phytotoxic herbicides that are widely used around the world for the pre- and postemergence control of a wide range of annual and perennial grasses and broadleaf weeds. They have been detected in reservoirs and wetlands in the North American Great Plains with reported detection frequencies of 35% to 52%. Although the source of contamination is not known, high concentrations of a number of herbicides followed rain-fall-generated runoff, suggesting that surface runoff likely contributed to the herbicide loadings. In order to assess the potential contribution of surface runoff, transport of two sulfonylurea herbicides (thifensulfuron-methyl and tribenuron-methyl) was measured in surface runoff from a flood-irrigated wheat field in the Outlook Irrigation District of Saskatchewan, Canada.

Five days after application of thifensulfuron-methyl and tribenuron-methyl for in-crop control of broadleaf weeds in late June (4-leaf stage), the field was irrigated using the border dyke method and surface runoff was monitored. Surface drain flow rates and herbicide concentrations were measured from three 0.85 ha (2.1 ac) plots in the field. Flow rates were calculated by applying the Manning equation to water depths measured in a culvert downstream from the plots using a sonic water level sensor. Automated water samplers were programmed…