Spray drift potential of dicamba plus S-metolachlor formulations

Authors: VIEIRA, BRUNO - University Of Nebraska; ALVES, GUILHERME - University Of Nebraska; VUKOJA, BARBARA - University Of Nebraska; VINICIUS, VELHO - University Of Nebraska; ZARIC, MILOS - University Of Nebraska; HOUSTON, TRENTON - University Of Nebraska; Fritz, Bradley - Brad; KRUGER, GREG - University Of Nebraska

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2021
Publication Date: 12/29/2022
Citation: Vieira, B., Alves, G., Vukoja, B., Vinicius, V., Zaric, M., Houston, T., Fritz, B.K., Kruger, G. 2022. Spray drift potential of dicamba plus S-metolachlor formulations. Pest Management Science. https://doi.org/doi 10.1002/ps.6772.
DOI: https://doi.org/10.1002/ps.6772

Interpretive Summary: Tank mixtures can have a significant effect on the droplet size resulting from a spray application potentially resulting in a large number of smaller, driftable droplets that can cause serious off-target damage. Understanding these impacts, particularly for new formulation technologies, is key to proper nozzle selection and use. Two herbicide formulations, one an advanced chemistry technology, were evaluated for spray droplet size, drift, and off-target damage. The results showed that poor nozzle selection combined with the wrong tank mixture can significantly increase fine droplet formation in the spray and cause significant downwind biological damage, particularly to plant species that may be susceptible to a given chemistry. However, the use of improved formulation technologies coupled with proper nozzle selection can significantly reduce the potential for off target movement and damage to non-target species.

Technical Abstract: Early-postemergent herbicide applications in the US often include residual herbicides such as S-metolachlor to suppress late germination flushes of Amaranthus spp. Although this practice benefits weed control, herbicide tankmixes can influence spray droplet size and drift potential during applications. The addition of S-metolachlor products to dicamba spray solutions generally decreases spray droplet size and increases spray drift potential. Advances in formulation technology fostered the development of products with reduced spray drift potential, especially for herbicide premixes containing two or more active ingredients. The objective of this study was to compare the drift potential of a novel dicamba plus S-metolachlor premix formulation (capsule suspension) against conventional tankmix containing dicamba (soluble liquid) and S-metolachlor (emulsifiable concentrate) using different venturi nozzles. The MUG nozzle had greater DV0.5 (1128.6 µm) compared to ULDM (930.3 µm), TDXL-D (872.9 µm), and TTI nozzles (854.8 µm). The premix formulation had greater DV0.5 (971.0 µm) compared to the conventional tankmix (922.3 µm). Nozzles influenced spray drift deposition (p<0.0001) and soybean biomass reduction (p=0.0465). Herbicide formulation influenced spray drift deposition (p<0.0001), soybean (p<0.0001), and cotton (p=0.0479) biomass reduction. The novel capsule suspension formulation (premix) of dicamba plus S-metolachlor had reduced spray drift potential compared to the conventional tankmix. Applications using the MUG nozzle had reduced spray drift potential compared to the other venturi nozzles. Study results evidence that advances in pesticide formulation can improve pesticide drift mitigation. The adoption of multiple techniques is essential to ensure efficient pesticide delivery while mitigating off-target movement to the surrounding environment.