EFFECT OF SIMULATED RAINFALL ON LEACHING AND EFFICACY OF FENAMIPHOS

There is increasing concern in the United States about the pesticide m ovement in soil, groundwater contamination, and pesticide residue in f ood. The objective of this study was to determine the efficacy, degrad ation, and movement of fenamiphos (Nemacur 15G) in the soil and residu es in squash fruit as influenced by four simulated rainfall treatments (2.5 or 5.0 cm each applied 1 or 3 days after nematicide application) under field conditions. In 1990, concentrations of fenamiphos were gr eater in the top lj cm of soil in plots with no rainfall than in those treated with rainfall. Eighty to 95% of the fenamiphos recovered from treated plots was found in the 0-15-cm soil layer. The concentration of fenamiphos recovered from the 0-15-cm soil layer in 1991 was approx imately one-half the concentration recovered in 1990, but greater conc entrations of fenamiphos sulfoxide (an oxidation product of fenamiphos ) were recovered in 1991 than in 1990. Concentrations of fenamiphos, f enamiphos sulfoxide, and fenamiphos sulfone were near or below detecta ble levels (0.002 mg/kg soil) below the 0-15-cm soil layer. Rainfall t reatments did not affect the efficacy of the nematicide against Meloid ogyne incognita race 1. The concentration of fenamiphos in squash frui t in 1991 was below the detectable level (0.01 mg/kg).