Agronomy and Horticulture Department


Date of this Version



Agron. J. 111:1425–1432 (2019)


Copyright © 2019 by the American Society of Agronomy

This document is a U.S. government work and is not subject to copyright in the United States.



The delivery of an optimum herbicide droplet size using pulse-width modulation (PWM) sprayers can reduce potential environmental contamination, maintain 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 6 site-years. The objectives were 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 pre-mixture and to create novel weed management recommendations using PWM sprayer technology. A pooled site-year generalized additive model explained less than 5% of the model deviance, so a site-specific analysis was conducted. Across the Mississippi and North Dakota sites, a 900-μm (Ultra Coarse) droplet size maintained 90% of the maximum weed control. In contrast, at the Nebraska sites, droplet sizes between 565 and 690 μm (Extremely Coarse) were almost exclusively required to maintain 90% of the maximum weed control, likely due to weed leaf architecture. Severe reductions in weed control were observed as droplet size increased at several site-years. Alternative drift reduction practices must be identified; otherwise, weed control reductions will be observed. 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 application parameters and conditions.