Effect of adjuvant types and concentration on spray drift potential of different nozzles

Abstract: Pesticide exposure via spray drift can have a negative impact on bystanders, residents, livestock, terrestrial and aquatic ecosystems. Reducing pesticide spray drift and maximizing efficacy are the paramount considerations when selecting technologies and operating parameters prior to making an application. With the increasing awareness about the potential risk of pesticides, many mitigation measures for pesticide exposure via spray drift have been developed. The effect of spray adjuvant and pesticide formulations is not yet well evaluated and implemented into drift mitigation scenarios. It is often stated that drift reduction with an appropriate nozzle is greater than those achieved by formulated products or spray adjuvant. In fact, to explore the combined effect of nozzle type and physical properties of spray liquids is also important. In order to study effect of adjuvant on spray drift potential of different nozzles, we used wind tunnel, and spectrofluorophotometor to carry out experiment which focused on how concentration of anti-evaporation adjuvant Agrospred 730（AS-2）, anti-drift adjuvant Break-thru Vibrant, Silwet DRS-60 and Greenwet 360 were affected by Drift Potential Index (DIX) of conventional flat fan nozzle Lechler ST 110-015, hollow cone nozzle TR 80-015, reference nozzle Lumark F110-03 and rotary nozzle. It has been reported in literature that the amount of spray drift is usually related to the percentage of fine spray droplets. The smaller a spray droplet, the longer it remains as airborne and the higher the possibility for it to be carried away by crosswind. Moreover, spray droplets of a few microns in size can evaporate before sedimentation. Therefore, it is fundamentally important to measure droplet size and the size distribution to understand the environmental and the biological fate of spray droplets. In this article, Malvern particle sizer was used to test Volume Median Diameter (VMD) and the percentage of droplets with diameter <75 μm of the four nozzles above. The concentration of AS-2 solution was 0, 0.005 %, 0.05 %, 0.5 %, the concentration of Break-thru Vibrant solution was 0, 0.1%, 0.2%, 0.4 %, the concentration of Silwet DRS-60 solution was 0, 0.1%, 0.2%, 0.4%, 0.8% and the concentration of Greenwet 360 solution was 0, 0.3% respectively. In the test, Pyranine 120% (0.01%) tracers were used to test and analyze the spray drift potential. The results showed that: when spraying 0.05% solution with anti-evaporation adjuvant AS-2, DIX of rotary nozzle (6 000 r/s, 400 mL/min) increased 81.8%, VMD increased 16.7% compared with water under the condition of which wind speed was 1.8 m/s, temperature was 30oC, humility was 40% in the wind tunnel. With the concentration of 0.8%, 0.4% and 0.3%, respectively, anti-drift adjuvant Silwet DRS-60, Break-thru Vibrant and Greenwet 360 can significantly reduce the spray drift. Especially for TR 80-015, DIX decreased 98.7%, 58.2% and 80.1% separately with the adjuvant above compared with water. The drift reduction performance of three hydraulic nozzles was TR80-015>ST110-015>Lumark F110-03 under the condition of which wind speed was 2 m/s, temperature was 20℃, humility was 80 % in the wind tunnel. For rotary nozzle, DIX decreased 70.3 % and 26.0 % with 0.8% Silwet and 0.3 % Greenwet 360 separately, while Break-thru Vibrant had no effect on it. For Silwet DRS-60 and Greenwet 360, DIX increased as the volume percentage of droplets with diameter <75 μm increased which showed positive correlation (the correlation coefficient R>0.5); DIX decreased as VMD increased which showed negative correlation, so VMD and volume percentage of droplets with diameter <75 μm were considered to be important factors affecting drift potential.