Influence of oil droplet size on the toxicity of bifenthrin on cotton to tobacco budworm (Heliothis virescens)

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.

Deposit structure and efficacy of pesticide application. 1: Interactions between deposit size, toxicant concentration and deposit number

“…However, larvae treated with small droplets (97 mm) lived longer than those with large droplets (337 mm). 25 This is consistent with our results where more uniform deposit structures resulted in longer survival times.…”

Coverage and Drift Produced by Air Induction and Conventional Hydraulic Nozzles Used for Orchard Applications

“…Laboratory studies reported by Himel (1969), Wofford et al (1987), Adams and Hall (1989), Hall et al (1990), and Omar et al (1991) generally found that smaller droplet sizes provided better insect control. However, Womac et al (1994) and Ebert et al (1999) found that small droplet sizes did not necessarily provide any better insect control. Studying deposition on vertical and horizontal canopy surfaces, Spillman (1984) reported that droplets 250 mm or larger had the highest deposition efficiency on leaves, while much smaller droplets (20 to 50 mm) produced the highest deposition efficiency on vertical surfaces as well as the undersides of leaves.…”

Droplet Size and Spray Volume Effects on Insecticide Deposit and Mortality of Heliothine (Lepidoptera: Noctuidae) Larvae in Cotton

“…In summarizing research from several authors, Adams et al (1990) reported that "almost all the studies indicated that the most efÞcient utilization of AI was associated with the smallest droplet size and the lowest concentration of the pesticide." Conversely, Womac et al (1994) reported that larger droplets of bifenthrin applied in parafÞnic oil for control of third-instar tobacco budworm were more effective than smaller droplets. Atypically, large droplets have been avoided by heliothine larvae under some conditions, (Polles 1968), a fact that adds yet another parameter to an already complex puzzle.…”