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R.J. Hilton, H. Riedl and P.H. Westigard

Handgun treatments of abamectin and oil applied between mid-June and late August caused distinct epidermal rings where drops of spray liquid dried on the surface of pear fruit (Pyrus communis L.). The severity of epidermal injury was related to the concentration of oil in the abamectin spray mixture (abamectin applied without oil caused no fruit damage). Of six pear cultivars tested, `Anjou' was most susceptible to injury, followed by `Cornice' and `Bartlett'. `Sensation Red Bartlett', `Bosc', and `Seckel' showed little or no phytotoxicity symptoms from abamectin and oil treatments with oil concentrations from 0.125% to 2.0% (v/v). On sensitive cultivars, the concentration of oil should not exceed 0.25% (v/v) when combined with abamectin to reduce the risk of epidermal injury. Oil at 0.25% provides for adequate leaf penetration of abamectin and results in commercially acceptable spider mite (Tetranychus urticae Koch) control. Chemical names used: avermectin B1 (abamectin).