EFFECT OF SIMULATED RAINFALL ON EFFICACY AND LEACHING OF 2 FORMULATIONS OF FENAMIPHOS

Recoverable fenamiphos in the soil and residue in squash following dif ferent simulated rainfall treatments after nematicide application were determined in a 5-year study. Efficacy of fenamiphos also was evaluat ed. Fenamiphos treatments (3 SC and 15 G) were broadcast (6.7 kg a.i./ ha) over plots and incorporated into the top 15 cm of soil immediately before planting 'Dixie Hybrid' squash. Simulated rainfall treatments of 0, 2.5, and 5.0 cm water were applied 1 day after fenamiphos applic ation. Soil samples from 0- to 8-cm, 8- to 15-cm, and 15- to 30-cm soi l depths were collected 1 day after the simulated rainfall application s and analyzed for fenamiphos, fenamiphos sulfoxide (FSO), and fenamip hos sulfone (FSO2). Squash was analyzed for total fenamiphos residue. Greater concentrations of fenamiphos were present in the 0- to 8-cm so il layer following application of 15 G than 3 SC formulation. Simulate d rainfall treatments did not alter fenamiphos concentrations in any s oil layer (except for the 0- to 8-cm depth in 1992) or concentration o f FSO and total fenamiphos residue in the 15- to 30-cm soil layer. Roo t-gall indices were greater from untreated than most fenamiphos-treate d plots, but were not affected by formulations of fenamiphos or simula ted rainfall treatments. Concentrations of total residue in squash ran ged from 1 to 4 mu g FSO2/g.