AVAILABILITY OF FENAMIPHOS AND ITS METABOLITES TO SOIL-WATER

Field and greenhouse experiments were conducted to determine the exten t to which fenamiphos and its degradation products, fenamiphos sulfoxi de and fenamiphos sulfone, are available to contact nematodes in the s oil. Water extraction provided a relative measure of each chemical's a vailability to the soil water where the chemicals could contact nemato des, and methanol extraction provided a relative measure of the total amount of each chemical present in the soil. Only small amounts of fen amiphos and fenamiphos sulfone could be extracted by water, even when much larger amounts were present in the soil. In contrast, virtually a ll of the fenamiphos sulfoxide present in the soil was extractable by water several days after nematicide application. Three days after fena miphos (3EC) was applied at 6.7 kg a.i./ha to field plots, 6.4% of the fenamiphos, 14.4% of the fenamiphos sulfone, and 100% of the fenamiph os sulfoxide present in the soil was extracted by water. In greenhouse experiments with soil from these field plots, a 15G formulation of fe namiphos containing 98.7% fenamiphos and 1.3% fenamiphos sulfoxide was added to the soil. After an initial period of 3-4 days, the sulfoxide which formed by oxidation of fenamiphos became completely available f or water extraction, whereas fenamiphos remained relatively unextracta ble by water. Fenamiphos sulfoxide is much more available to soil wate r, thus available for contact with nematodes, than are fenamiphos or f enamiphos sulfone. Based on this availability in water, it seems likel y that fenamiphos sulfoxide is the major component for controlling nem atodes.