Factors Affecting Toxicity of Propargite to the European Red Mite (Acari: Tetranychidae)

Laboratory tests with adult female European red mites, Panonychus ulmi (Koch), showed that toxicity of propargite was correlated with temperature; toxicity was 4.75-fold higher at 24°C than at 15°C. Mortality of female European red mites was higher on foliage treated with an emulsifiable (6 EC) formulation of propargite than with a wettable powder (30 WP) formulation both in the laboratory and in the field. In laboratory tests, higher mortalities were observed on peach compared with apple foliage. Investigations using the scanning electron microscope, fluorescent dyes, and analysis of field-treated foliar residues did not explain the increased toxicity of the emulsifiable formulation. Scanning electron microscope studies showed discrete deposits formed from dried spray droplets of propargite 30 WP suspension on leaf surfaces, but there were no visible deposits on leaf surfaces treated with propargite 6 EC. Deposits of both formulations mixed with fluorescent dye appeared similar under short-wave ultraviolet light. Amounts of residue recovered from 6 EC and 30 WP applications to field-treated apple foliage were dependent on initial application rates of both formulations and were not associated with a particular formulation. Rate of residue loss for the EC formulation was not significantly different than that for the WP formulation.