PESTICIDE FATE IN TURF - STUDIES USING MODEL-ECOSYSTEMS

The fate of DCPA and isazofos in turfgrass was studied in specially designed model ecosystems. The effect of irrigation frequency and the presence of thatch on the fate of DCPA was monitored over an eight week period. Of the six soil type/irrigation frequency treatments, only the sandy soil with thatch irrigated every fourth day had less than 50% of the applied dose of DCPA remaining after 8 weeks. All other treatment combinations had between 67 and 95% of the applied DCPA remaining after 8 weeks. No volatility or evolution of (CO2)-C-14 was detected. The principal route of DCPA dissipation was cleavage of the methyl ester groups to the corresponding acid and subsequent leaching of these mobile metabolites. Between 1 and 25% of the applied DCPA was detected as metabolites in the leachate. The fate of isazofos in two soil types with or without thatch was compared. The presence of turf had a small but consistent effect on the fate of isazofos. Where turf was present, isazofos degraded more rapidly with only 5% remaining after 4 weeks with a Kentucky bluegrass turf whereas 13% remained in the same soil without turf. Soil unextractable material accumulated more rapidly in soils where turf was present indicating a more active microbial biomass. The major metabolite detected, CGA-17193, accumulated rapidly in all soil types with between 20 to 60% of the applied radioactivity detected as CGA-17193 at one week after treatment. CGA-17193 was more mobile in soil than isazofos with 8 to 17% CGA-17193 found in the leachate compared to 1-5% of isazofos at 4 WAT.