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

The efficacy of the nematicide fenamiphos [ethyl-3-methyl-4-(methylthio)phenyl (1-methylethyl) phosphoramidate] often is reduced when applied annually or biannually for extended periods, to turf-grasses in Florida. This study was conducted near Gainesville, FL, on a Blichton sand (loamy, siliceous, hyperthermic Arenic Plinthic Paleaquults) to determine whether the degradation of fenamiphos was enhanced by long-term applications to a turfgrass golf course fairway and putting green. C-14-fenamiphos was used for determination of mineralization rates, metabolites, and mass balance. Initial mineralization of C-14-fenamiphos in soil collected from the turfgrass site was more rapid than in soil collected 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-life values for total toxic residues (TTR, fenamiphos + FSO + FSO2) in soil 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 fenamiphos application were smaller than in soil collected before the application. Total C-14 recovery from C-14-fenantiphos-treated surface soil collected 0.7 mo after the annual application was well below 100%. Rapid initial mineralization of fenamiphos was also observed in this sample. Applications of fenamiphos to the same site for prolonged periods appear to increase the potential for enhanced degradation of TTR.