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 cerea ls. Diflufenican was applied at two sites presowing, each year for a f our-year period. Soil samples were analyzed immediately following appl ication, at 6 months and 12 months after application each year. In add ition, 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 y ear a cereal (wheat) and maize crop were grown at the two sites as mai n crop and rotational crop, respectively. Analysis of the crop parts s howed no residues in any of the wheat or maize plant parts in excess o f 0.001 mg/kg, the limit of determination. Results of the analysis sho wed a consistent steady decline each year with no change (enhancement or decrease) in the rate. There was no accumulation from one year to t he 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 be low the surface layer in the soil. A DT50 value of ca. 14 days was cal culated in the fourth year at one of the sites, followed by a more ste ady decline with a DT90 of 228 days.