Agronomy and Horticulture Department



Thomas R. Butts

First Advisor

Greg R. Kruger

Date of this Version



T. R. Butts, Spray Characterization and Herbicide Efficacy as Influenced by Pulse-Width Modulation Sprayers. PhD diss., Department of Agronomy & Horticulture, University of Nebraska–Lincoln, 2018.


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy Major: Agronomy & Horticulture (Weed Science) Under the Supervision of Professor Greg R. Kruger Lincoln, Nebraska August, 2018.

Copyright (c) 2018 Thomas R. Butts


Pesticide applications are a heavily scrutinized facet of today’s agricultural industry, and a concerted effort to optimize each application needs to be implemented. More precise and efficient pesticide applications are necessary to meet regulatory demands and increase economic efficiency through reduced pesticide inputs. Current pesticide application methods using precision technologies, including pulse-width modulation (PWM) sprayers, can assist with these goals. However, vast advancements in pesticide formulations, adjuvants, and nozzles, as well as the increasing popularity of PWM systems, have only increased the need for applied PWM and weed science research. Additionally, efforts have been placed on increasing spray droplet size to reduce particle drift, but this practice has led to reduced herbicide efficacy. Therefore, identifying an optimum herbicide droplet size which can reduce particle drift while simultaneously maintaining efficacy is a necessity.

The objectives of this research were to: (1) identify the influence of application parameters on droplet size, droplet exit velocity, nozzle tip pressure, and spray pattern uniformity from a PWM sprayer, (2) create best use PWM recommendations to optimize pesticide applications from these sprayers, (3) investigate the effect of spray droplet size and carrier volume on the efficacy of multiple herbicide solutions, (4) establish novel weed management recommendations based on an optimum droplet size, and (5) determine the plausibility of using PWM sprayers in site-specific weed management strategies.

The results of this research have led to more precise PWM sprayer operation through clear and concise best use recommendations. The capability of PWM sprayers to make precise and uniform applications can assist with the reduction of spray particle drift and increase the overall application effectiveness. Additionally, site-specific weed management strategies were effectively established and optimum herbicide droplet sizes were estimated across a wide range of geographies and weed species. Although, convoluted interactions were identified between droplet size, carrier volume, and other application parameters in regards to their effect on herbicide efficacy. As a result of this research, applicators can more effectively utilize PWM sprayers, reduce herbicide inputs, mitigate spray particle drift, and reduce the selection pressure for the evolution of herbicide-resistant weeds.

Advisor: Greg R. Kruger

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Agriculture Commons