| Abstract: | Sprays of bifenthrin and paraffinic oil mixtures were applied to cotton leaves (Gossypium hirsutum L.) to investigate droplet size effects on the mortality of Heliothis virescens (F.). An air-assisted nozzle applied mixtures at 9.4 litre ha ?1 spray rate with volume median diameters (VMD) of 96 and 337 μm, as verified with a Malvern laser diffraction analyzer. An hour after spraying, susceptible 3rd-instars walked for 2-min through wet droplets of spray mixtures applied at bifenthrin rates of 22, 45, 67, 90. and 112 g a.i. ha ?1. Mortality was assessed at 21, 26, 45, 50, 74, and 117h after exposure. Final mean mortality was affected (P =0.01) by bifenthrin rate and droplet size. Bifenthrin applied in 337 μm VMD droplets caused 75.8% mortality, whereas 96-μm VMD droplets resulted in a mortality of 67.9%. Also, the 337 μm VMD droplets killed larvae in 13% less time than the 96μm VMD droplets, based on analysis (P =0.01) using the mean elapsed time till death as the dependent factor. |
