TOXICITY AND DETERRENCY OF DEPITCHED TALL OIL TO THE GREEN PEACH APHID, MYZUS-PERSICAE

The comparative toxicity and deterrency of depitched tall oil, a by-product of the kraft process for pulping softwood, and Superior 70 oil, a common horticultural oil, to the green peach aphid. Myzus persicae (Sulzer), were investigated. Leaf disc choice bioassays using second-instar M. persicae indicated that both depitched tall oil and Superior 70 oil deter aphids in a dose-dependent manner. Effective concentrations resulting in 50% deterrence (EC50 values) (with 95% confidence interval) for depitched tall oil and Superior 70 oil were 0.88% (0.78-0.98) and 1.39% (1.17-1.60), respectively. Depitched tall oil was significantly (p < 0.05) more deterrent to aphids than Superior 70 oil. Depitched tall oil and Superior 70 oil were equally toxic to second-instar M. persicae when leaf discs were treated with the test materials. Concentrations causing 50% mortality (LC50 values) for depitched tall oil and for Superior 70 oil were 1.05 and 1.10%, respectively. At a concentration of 1%, depitched tall oil applied to leaf discs reduced aphid survival to 28% after 5 days, whereas survival of controls was 78%. When topically applied at a dose of 0.1 mul per aphid, the lethal doses of depitched tall oil resulting in 50% mortality (LD50 values) at 72 h for second-instar and adult M. persicae were 0.16 and 0.20 mug per aphid, respectively. When sprayed at a dose of 5 mul cm-2, the LC50 values at 72 h for emulsified depitched tall oil to second-instar and adult M. persicae were 1.08 and 0.80%, respectively. The deterrent effect of depitched tall oil on M. persicae persisted for at least 3 days under greenhouse conditions.