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Title: Optimum droplet size using a pulse-width modulation sprayer for applications of 2,4-D choline plus glyphosate

item BUTTS, THOMAS - University Of Nebraska
item SAMPLES, CHASE - Mississippi State University
item FRANCA, LUCAS - Mississippi State University
item DODDS, DARRIN - Mississippi State University
item REYNOLDS, DANIEL - Mississippi State University
item ADAMS, JASON - North Dakota State University
item ZOLLINGER, RICHARD - North Dakota State University
item HOWATT, KIRK - North Dakota State University
item Fritz, Bradley - Brad
item HOFFMANN, WESLEY - Former ARS Employee
item LUCK, JOE - University Of Nebraska
item KRUGER, GREG - University Of Nebraska

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2018
Publication Date: 2/21/2019
Publication URL:
Citation: Butts, T., Samples, C., Franca, L., Dodds, D., Reynolds, D., Adams, J., Zollinger, R., Howatt, K., Fritz, B.K., Hoffmann, W.C., Luck, J., Kruger, G. 2019. Optimum droplet size using a pulse-width modulation sprayer for applications of 2,4-D choline plus glyphosate. Agronomy Journal. 111(1):1425-1432.

Interpretive Summary: Precise application of herbicide products is crucial to successful management of weeds while reducing environmental contamination and off-target impacts. Spray delivery systems should be setup to deliver optimum droplet sizes, while maintaining spray rate, to adapt spray applications to changes in weed species, weather conditions and geographical changes to ensure product efficacy. A pulse width modulation system, which allows for these types of changes, was used to determine site-specific product efficacy across multiple field sites and weed species to determine optimum spray droplet size required to maximize efficacy while minimizing off-target movement. While optimum droplet size varied across location and weed species, the results demonstrated that coarse sprays with low drift potential provided acceptable weed control in all cases. The pulse width modulation system provides an easy method for optimizing a spray delivery system to provide the spray droplet size needed for site-specific conditions to ensure product efficacy and minimize non-target damage.

Technical Abstract: The delivery of an optimum herbicide droplet size using pulse-width modulation (PWM) sprayers can reduce potential environmental contamination, maintain satisfactory efficacy, and provide more flexible options for pesticide applicators. Field research was conducted in 2016, 2017, and 2018 across three locations (Mississippi, Nebraska, and North Dakota) for a total of six site-years. The objective was to evaluate the efficacy of a range of droplet sizes [150 µm (Fine) to 900 µm (Ultra Coarse)] using a 2,4-D choline plus glyphosate (Enlist Duo) pre-mixture and create novel weed management recommendations utilizing PWM sprayer technology. Across pooled site-years, a 430 µm (Coarse) droplet size maintained 90% of the maximum weed mortality, thereby reducing the addition of weed seeds to the soil seedbank and mitigating spray particle drift potential. However, model fit was poor, so a site-specific analysis was conducted. Across the Mississippi and North Dakota sites, a 900 µm (Ultra Coarse) droplet size was recommended. In contrast, at the Nebraska sites, droplet sizes between 565 – 690 µm (Extremely Coarse) were almost exclusively required to maintain 90% of the maximum weed control likely due to weed leaf architecture. This research illustrated that PWM sprayers paired with appropriate nozzle*pressure combinations for 2,4-D choline plus glyphosate pre-mixture could be effectively implemented into precision agricultural practices by generating optimum herbicide droplet sizes for site-specific management plans. To fully optimize spray applications using PWM technology, future research must holistically investigate the influence of weather conditions, time of day, weed species, geographic location, and herbicide droplet size.