Influence of Adjuvants and Air Velocity on Spray Drift Deposition in Wind Tunnel Applications of a Bacillus thuringiensis-Based Bioinsecticide

Most studies in the field of application technology have focused on the interaction between adjuvants and agrochemicals, highlighting the need for further research to evaluate the behavior of adjuvants in association with other classes of crop protection products. In this context, the objective of this study was to evaluate the influence of adjuvants and air velocity on spray drift deposition in simulated applications conducted in a wind tunnel using a bioinsecticide based on Bacillus thuringiensis. The experiment was carried out in an open-circuit, blower-type wind tunnel installed at the Agricultural Machinery Laboratory of the State University of Goiás – Central Campus. The study was conducted in a completely randomized design arranged in a 5 × 4 × 4 factorial scheme, with three replications. Treatments consisted of five horizontal distances from the spraying point (0.45, 0.75, 1.05, 1.35, and 1.65 m), four wind speeds inside the tunnel (1, 2, 3, and 4 m s⁻¹), and four spray solution formulations (water + dye; bioinsecticide + dye; bioinsecticide + vegetable oil + dye; and bioinsecticide + surfactant + dye). For deposition sampling, artificial targets were positioned transversely to the airflow and, immediately after spraying, were divided into lower, middle, and upper thirds relative to the height of the test section. Data were obtained by spectrophotometry and, after verifying the ANOVA assumptions, subjected to ANOVA (P < 0.05). When significant, mean comparisons and regression analyses were performed. Statistical analyses were conducted using the R and Sisvar software packages. Mean deposition values were converted into drift percentage as a function of the total sprayed volume. The experimental data were also subjected to geostatistical analysis using GS+ software (Version 7®). After confirming spatial dependence, contour maps were generated using kriging. Higher wind speeds led to higher drift percentages. The use of the adjuvant Break Thru® contributed to reducing drift in the upper and middle thirds. In the lower third, at a wind speed of 1 m s⁻¹, the addition of Break Thru® reduced drift; however, at 4 m s⁻¹, adjuvants did not reduce deposition compared to the spray solution prepared with the biological insecticide. The analyzed variable showed a strong spatial dependence across all treatments.