Exposure and risk to non-target receptors for agricultural spray drift of formulation types and adjuvants

Abstract

Agricultural applications of crop protection products can have negative economic and ecological consequences when spray drift occurs. Among the ways to reduce spray drift is to manipulate the physical properties of the spray solution with formulated products and tank additives, but further research is required to better understand their effects. By measuring spray drift under field conditions and using the results to estimate ecological risk, we characterize the effect on drift for two formulation types and two adjuvants. A field study was conducted where off-target ground deposition and droplet size were measured to indicate spray drift for different combinations of the formulations and adjuvants, accounting for environmental conditions. Each treatment combination was also sprayed in a wind tunnel set up to precisely measure droplet spectra so that these could be related to deposition in the field. Finally, an efficacy experiment was conducted to test for tradeoffs between drift reduction and pest control. Results from the field study suggest that as much as 32% drift reduction was achieved by selecting between the tested formulation types, and as much as 62% by incorporating certain spray adjuvants, but this effect depended on the formulation/adjuvant combination. Treatments with smaller droplet sizes had greater drift, and there was no tradeoff between drift reduction and pest control. We assessed ecological risk for terrestrial insects in non-target habitats using a novel approach to estimate insecticide residue on plant surfaces based on ground deposition data from the field study. Exposure concentrations were combined with a cumulative distribution of species sensitivities to statistically represent the risk of toxicity for the active ingredient that was used and the levels of drift that were observed. We found that substantial reductions in the percentage of insect species affected in an off-target area could be achieved by certain formulation types and adjuvants. This work could be useful for developing a classification scheme for formulated products and tank additives based on their potential for reducing spray drift and ecological risk to non-target receptors.