Persistence and Mobility of Isazofos in Turfgrass Thatch and Soil

Isazofos was applied to turfgrass as an emulsifiable concentrate (480 g/liter) at 2.24 kg (AI)/ha. Irrigation regimes included application of 10.2 liters/m2 water immediately, and 8, 24, and 36 h after treatment. Persistence and movement of the insecticide was measured by gas chromatographic analyses of core samples of thatch, and first and second 2.5 cm of soil at 3 h, 3 d, and 1, 2, 4, 8, 36 wk after treatment. Green grass was removed and not analyzed. The thatch contained 96–99% of detectable residues recovered with a range of 0.123 (8 wk) to 3.57 ppm (3 h). Immediate posttreatment irrigation resulted in significantly higher residues in the thatch during the first 2 wk of sampling. Residues in the first and second 2.5 cm soil during the 8-wk sampling period ranged from 0.002 to 0.04, and 0.024 to < 0.001 ppm, respectively. At 36 wk, residues were ≤0.045 in the thatch, ≤0.003 in the first, and ≤0.001 ppm in the second 2.5 cm soil. Although useful in moving the insecticide off the grass blades and into the thatch, posttreatment irrigation had no significant effect on movement of the insecticide into the soil.