PESTICIDE DISSIPATION UNDER GOLF COURSE FAIRWAY CONDITIONS

The degradation and vertical movement of pendimethalin, chlorpyrifos, isazofos, and metalaxyl were monitored in Kentucky bluegrass (Poaprate nsis L.) turf managed as a golf course fairway. Intact turf-soil cores from Mead, NE, on a Sharpsburg soil (fine montmorillonitic, mesic Typ ic Argiudoll) and Gilbert, IA, on a Nicollet loam (fine-loamy, mixed, mesic Aquic Hapludoll) planted to Kentucky bluegrass were periodically removed to 60-cm depth through 113 d after pesticide application. Cor es were sectioned into verdure, thatch, and multiple soil depths. Whil e verdure contained high pesticide concentrations after application, p recipitation, and clipping, and degradation reduced the amount in plan t tissue with time. Thatch was highly retentive of the pesticides, gen erally containing the most residue throughout the monitoring period. P esticide residues tended to be lower in soil at the Iowa site where mo re thatch was present. Little chlorpyrifos or pendimethalin moved thro ugh the thatch to the underlying soil. Isazofos was more mobile and me talaxyl moved through the entire soil column. Soil contained an averag e of 58% less pesticide than thatch over all sampling times, and conce ntrations in soil were highest at the 0- to 5- and 5- to 10-cm depths. Average time for 50% dissipation in the turf-soil profile (DT50) was 16, 12, 10, and 7 d for metalaxyl, pendimethalin, chlorpyrifos, and is azofos, respectively. The pesticides appeared to degrade more rapidly in the turfgrass environment than typically reported for other agronom ic cropping systems. Variability in pesticide residue concentrations f or each soil depth among the turf-soil cores indicated non-uniform dis sipation in the field.