Effects of Spray Drop Size and Distribution of Drops Containing Bifenthrin on Tetranychus urticae (Acari: Tetranychidae)1

Uniform drops of 120, 145, and 200 μm containing 0.075% (0.18 g [AI]/liter) bifenthrin 2E were deposited on lima bean leaf disks (1.77 cm2) in distributions ranging from 0 to 182 drops per square centimeter to study effects on the twospotted spider mite, Tetranychus urticae Koch. Based on regression analysis of data, egg deposition was reduced 80% with 41 drops per square centimeter of 120 μm (0.007 μg [AI]/cm2) or 18 drops per square centimeter of 200 μm (0.014 μg [AI]/cm2). The 41 drops per square centimeter of 120μm correspond to 3.7 liters/ha and 18 drops per square centimeter of 200 μm correspond to 7.5 liters/ha. Eighty percent of the mites were repelled from leaf disks with either 251 drops per square centimeter of 120μm (0.041μg [AI]/cm2) or 51 drops per square centimeter of 200 μm (0.040 μg [AI]/cm2). Droplets of 120 μm were more efficient in pesticide and water usage than 200-μm drops in decreasing egg production and nearly as efficient in repelling adult mites.