Factors affecting the biological efficiency of small pesticide droplets against <i>Tetranychus urticae</i> eggs

Abstract

Abstract Using monosized oil‐based droplets of dicofol against Tetranychus urticae eggs on 1 cm 2 discs of bean leaf, the effects of varying droplet diameter (18–146 μm) and concentration of active ingredient (0.5–40 g litre −1 ) on egg mortality were investigated. A positive curvilinear relationship was found between the spacing of droplets required to produce 50% kill (LS 50 ) and the original diameter of the droplet, D, such that: where b varied from 0.65 to 1.44 and bore a U‐shaped relationship to concentration. Thus, there was an optimum concentration of about 10 g litre −1 , with control efficiency reducing as much as nine times at the extreme concentrations, and even more from the smallest to the largest droplets. The theoretical, practical and economic implications are discussed.