Degradation of parathion applied to peach leaves

Parathion was applied to peach trees in three different formulations 70 days before harvest. Leaf samples were taken periodically through the 70-day period and gas-liquid chromatographic analyses were conducted for dislodgable and penetrated residues. Analyses were also conducted for paraoxon and the s-ethyl isomer of parathion. Punched samples were compared to whole-leaf samples; generally residue levels for both types corresponded closely. A new experimental formulation, encapsulated parathion, produced highest levels of total parathion throughout the 70-day study, but even this formulation resulted in low total residue levels around 1 ppm at time of harvest. Degradation of the s-ethyl isomer of parathion was generally very rapid in all formulations studied. Dislodgable residues of paraoxon may be significant in some formulations and should be included in parathion degradation studies. Much of the parathion found on peach leaves throughout the growing season was dislodgable residue, but this depended considerably on the formulation used.