Cyhexatin Resistance and Enhancement with Calcium Chloride in Washington State Populations of Spider Mites (Acari: Tetranychidae) on Pome Fruit

Abstract

The enhancement of calcium salts, primarily calcium chloride, to the efficacy of cyhexatin in Washington populations of twospotted spider mite (TSSM), Tetranychus urticae Koch, McDaniel spider mite (MSM), Tetranychus mcdanieli McGregor and European red mite (ERM), Panonychus ulmi (Koch) was evaluated in the laboratory and in commercial apple orchards. Laboratory techniques used to test the 50WP, 5F and technical 85% cyhexatin were the slide-dip, leaf disk and leaf spray bioassays. Bioassay responses by various spider mite populations to cyhexatin and calcium salts indicated that the leaf spray method was most appropriate on apple foliage and that calcium chloride increased cyhexatin 50WP toxicity 6-fold for ERM and 31-fold for TSSM. The toxicity of formetanate 92SP, propargite 30WP, dicofol 1.6EC and fenbutatinoxide 4L was not increased by combining with CaCl2. Under field conditions, efficacy trials with ERM and MSM to cyhexatin and cyhexatin + CaCl2 indicated that differences between treatment means were significant, but less effective than were predicted from laboratory bioassays. Inconsistent field control was apparently associated with respective adjuvant/cyhexatin concentrations, tetranychid population susceptibility and physical variables inherently associated with orchard management practices.