Persistence of Foliar Residues of Dimethoate and Azinphosmethyl and Their Toxicity to the Apple Maggot12

Field tests indicated that dimethoate was more toxic than azinphosmethyl to adults of Rhagoletis pomonella (Walsh) caged on sprayed foliage. Based on probit analysis using foliar residues, the LC50 for dimethoate was 2–10 times less than that for azinphosmethyl. Time till 50% kill (ET50) was 5–10 days longer for dimethoate than for azinphosmethyl. EC formulations were not effective longer than wp formulations. Initial deposits of azinphosmethyl on foliage were higher than those of dimethoate regardless of formulation used. Highest initial deposits occurred when the EC formulation of azinphosmethyl was applied. Loss of residues from foliage closely fitted a 3 parameter asymptotic regression curve with the equation Y = A + BRx, where Y is the amount of residue remaining at time X, A is the asymptote of Y, B is the scaling constant, and R is the rate of degradation. Although azinphosmethyl residues persisted at higher levels than dimethoate throughout, the rate of loss was similar for each compound, regardless of formulation used.