Impact of carrier volume and spray droplet size on pesticide application efficacy in Mississippi

The application of pesticides in agriculture production systems is a complex process and involves a series of factors that dynamically interact to impact overall pesticide application efficacy. Spray droplet formation, target impaction and deposition, plant uptake, and subsequent biological response are all functions of pesticide active ingredient, nozzle selection, application pressure, and carrier volume. Smaller spray droplets with a lower kinetic energy result in greater spray droplet retention on the leaf surface relative to larger droplets. Consequently, larger spray droplets with higher kinetic energy are poorly retained on the leaf surface and yield minimal coverage of leaf surface tissue. While smaller droplets maximize target coverage and spray droplet retention, larger spray droplets minimize off-target movement and agrichemical transport. Consequently, application factors that maximize pesticide efficacy and minimize off-target movement are often incongruous elements. Therefore, the objective of this research was to evaluate the impact of carrier volume and spray droplet size on the efficacy of various pesticide applications in Mississippi. These data indicate that 1) for thrips and tarnished plant bug control, acephate and sulfoxaflor are superior dicamba application partners relative to dimethoate and thiamethoxam, respectively, insecticide efficacy did not vary due to spray droplet size when applied without dicamba, and maximum efficacy was achieved with a carrier volume of 187 L ha-1; 2) dicamba + acephate and dicamba + thiamethoxam or sulfoxaflor are efficacious options to control Palmer amaranth relative to dicamba applied alone, and maximum Palmer amaranth control was achieved with a carrier volume of 187 L ha-1; 3) cotton defoliation efficacy is positively and negatively correlated with carrier volume and spray droplet size, respectively, and maximum efficacy was achieved with cotton defoliation programs consisting of two-applications, each with a carrier volume of 187 L ha-1 and 200 µm droplets; 4) soybean harvest aid efficacy is primarily a function of the harvest aid applied and that the impact of carrier volume and spray droplet size varies across harvest aids. However, when paraquat is applied, a carrier volume between 47 and 187 L ha-1 should be utilized with droplets of 200-500 µm to maximize harvest aid efficacy