DEGRADATION OF FENAMIPHOS IN SOIL WITH A HISTORY OF CONTINUOUS FENAMIPHOS APPLICATIONS

The efficacy of the nematicide fenamiphos [ethyl-3-methyl-4-(methylthi o)phenyl (1-methylethyl) phosphoramidate] often is reduced when applie d annually or biannually for extended periods, to turf-grasses in Flor ida. This study was conducted near Gainesville, FL, on a Blichton sand (loamy, siliceous, hyperthermic Arenic Plinthic Paleaquults) to deter mine whether the degradation of fenamiphos was enhanced by long-term a pplications to a turfgrass golf course fairway and putting green. C-14 -fenamiphos was used for determination of mineralization rates, metabo lites, and mass balance. Initial mineralization of C-14-fenamiphos in soil collected from the turfgrass site was more rapid than in soil col lected from the rough (untreated). Fenamiphos sulfoxide (FSO) was the main metabolite detected, whereas fenamiphos sulfone (FSO2) was either not detected or only occasionally detected in trace amounts. Half-lif e values for total toxic residues (TTR, fenamiphos + FSO + FSO2) in so il samples collected from the site were all small, ranging from 0.9 to 4.2 d, and half-life values for TTR in soil collected after the fenam iphos application were smaller than in soil collected before the appli cation. Total C-14 recovery from C-14-fenantiphos-treated surface soil collected 0.7 mo after the annual application was well below 100%. Ra pid initial mineralization of fenamiphos was also observed in this sam ple. Applications of fenamiphos to the same site for prolonged periods appear to increase the potential for enhanced degradation of TTR.