Long-term degradation and potential plant uptake of diflufenican under field conditions

Diflufenican is a widely used highly effective residual herbicide used preemergence or early postemergence for the control of weeds in cereals. Diflufenican was applied at two sites presowing, each year for a four-year period. Soil samples were analyzed immediately following application, at 6 months and 12 months after application each year. In addition, at one of the sites in the last year, samples were taken over a more frequent time course to establish the pattern of decline. Each year a cereal (wheat) and maize crop were grown at the two sites as main crop and rotational crop, respectively. Analysis of the crop parts showed no residues in any of the wheat or maize plant parts in excess of 0.001 mg/kg, the limit of determination. Results of the analysis showed a consistent steady decline each year with no change (enhancement or decrease) in the rate. There was no accumulation from one year to the next, over the four-year period of the residual soil concentrations of diflufenican which were only slightly above 0.001 mg/kg the limit of determination. There was no evidence of movement of diflufenican below the surface layer in the soil. A DT50 value of ca. 14 days was calculated in the fourth year at one of the sites, followed by a more steady decline with a DT90 of 228 days.