The persistence of ethion and Zolone residues on grape foliage in the central valley of California

The hazard of serious intoxication of agricultural field workers by organophosphate insecticide residues has led to the establishment of reentry intervals in California. In the attempt to extend this concept nationally, it has been found that there is a lack of relevant field data for setting of such standards. In an effort to expand knowledge of the relationship between foliar residue levels and occupational hazard, an examination of the persistence and transport of ethion, Zolone, and their oxygen analogs on grape foliage was conducted. Both dislodgeable and penetrated residues were followed for 28 days post-application for both insecticides while soil surface residues were followed for ethion only.A marked difference is seen in the decay rates of the dislodgeable vs. the penetrated residues of ethion, the dislodgeable residues decaying more quickly. This difference is not apparent for Zolone. Of particular significance to worker hazard is the finding that the oxones of both ethion and Zolone in the dislodgeable residues reach a plateau after approximately seven days and do not degrade further by day 28.