Efficacy and persistence of chlorpyrifos residues on peaches for control of San Jose scale (Homoptera: Diaspididae) [Quadraspidiotus perniciosus]

Chlorpyrifos 4E at the rate of 0.6 g (AI)/liter provided control of San Jose scale, Quadraspidiotus perniciosus , on peaches. Toxic residues persisted for 60 to 80 days on twigs. At harvest, chlorpyrifos residues were 7 to 11-fold higher on twigs than on fruit. Two applications left a residue in the fruit of 0.053 ppm, just over the 0.05-ppm tolerance. Bioassays indicated the minimum lethal concentration (LC sub(95-99)) was between 0.51 and 0.73 ppm, or a residue of between 0.098 and 0.141 mu g/cm super(2) of twig surface.