Plant-Back Intervals of Imicyafos Based on Its Soil Dissipation and Plant Uptake for Rotational Cultivation of Lettuce and Spinach in Greenhouse

Abstract

The plant-back intervals (PBIs) of imicyafos were investigated for rotational cultivation of lettuce and spinach in greenhouses. Imicyafos dissipation in soil and its plant uptake were evaluated by liquid chromatography-tandem mass spectrometry. Bioconcentration ratios (BCRs) were calculated by comparing the residues in plants to the initial residue in soil. The BCRs were used to calculate the soil acceptable residues (SARs) transferable to plants at the Positive List System (PLS) level. The number of days, PBIs for reaching SARs were obtained from the dissipation equation for imicyafos in soil. In soil, imicyafos followed first order dissipation kinetics (R2 = 0.975) with a half-life of 40.8 days. The BCRs ranged from 0.041 to 0.469 in the edible leaf parts of lettuce and 0.006 to 0.134 in those of spinach. The SARs ranged from 0.021 to 0.244 for lettuce and 0.075 to 1.667 mg kg−1 for spinach. The PBIs of imicyafos were estimated to be 213.9 to 357.3 days for lettuce and 100.8 to 283.6 days for spinach. This study suggests at least a minimum 1-year interval after the final application of imicyafos as a management method that complies with the PLS for the rotational cultivation of lettuce and spinach.