Effect of Chlorpyrifos and Dimethoate Spraying Doses on Residue Concentrations in Scallion (Alliumcepa var. aggregatum)

Abstract

Residue concentrations of chlorpyrifos and dimethoate in scallion (Alliumcepa var. aggregatum.) were studied. The experimental design was split plot RCBD. The main factor was concentration of pesticide sprayed with 3 doses: 1) half recommended dose 2) recommended dose 3) double recommended dose and sprayed with water (control) and 5 replicates. Sprayed chlorpyrifos and dimethoate on days 21, 28 and 35. The minor factor was a period of harvesting after last sprayed on days 0 (2 hours), 1, 3, 5, 7, 10 15, 20 and 25. Two hours after application scallion from double recommended dose were found chlorpyrifos concentration higher than recommended dose and half recommended dose (12.23 ± 0.35, 5.27 ± 0.24, 2.67 ± 0.04 ppm, respectively). The MRL of chlorpyrifos on scallion are 0.05 ppm (EU MRL) and 0.01 ppm (Japan MRL). Then, chlorpyrifos slowly degraded until were less than MRL on day 15 after application. Two hours after last application, concentrations of dimethoate from double recommended dose, recommended dose and half recommended dose were 5.47 ± 0.28, 2.09 ± 0.15, 0.56 ± 0.03 ppm (respectively). The MRL of dimethoate on scallion are 2 ppm (EU MRL) and 1 ppm (Japan MRL). Then, dimethoate degraded faster than chlorpyrifos until they were less than MRL on day 3. Therefore, harvesting periods of chlorppyrifos and dimethoate on scallion planting should be more than 15 and 3 days, respectively.