Agronomy and Horticulture, Department of


First Advisor

Greg R. Kruger

Date of this Version


Document Type



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agronomy, Under the Supervision of Professor Greg R. Kruger. Lincoln, Nebraska : August, 2018.

Copyright (c) 2018 Jesaelen Gizotti de Moraes


Protoporphyrinogen oxidase (PPO)-inhibiting herbicides in combination with glyphosate for postemergence (POST) applications is one of the primary alternatives to manage glyphosate-resistant weeds and the only effective POST chemical option in conventional and glyphosate-tolerant soybean to control glyphosate and ALS-inhibiting resistant weeds. Antagonistic interactions have been reported between many different herbicide modes of action and optimal droplet size may be affected by tank-mixtures of different herbicides. Additionally, the impact of adjuvants on the factors aforementioned as well as on physical properties needs to be thoroughly investigate to maximize herbicide efficacy. Therefore, the objectives of this research were to: 1) conduct greenhouse and field studies to evaluate the impact of glyphosate and PPO-inhibiting herbicides (fomesafen or lactofen) applied alone and in tank mixtures on weed control, optimal droplet size, drift potential, and tank mixture interactions, 2) determine the influence of adjuvants on tank mixtures interactions, spray droplet-spectra, drift potential, and physical properties, (3) determine if herbicide efficacy (and thereby, weed control) is correlated to reduced surface tension and contact angle. Overall, applications from the tank mixtures resulted in antagonistic interactions and some of them were overcame by the addition of adjuvants. Droplet size and percent volume of droplets ≤ 150 µm were highly affected by nozzle type and spray solution. The oil based formulation of lactofen and crop oil concentrates were shattered by TTI nozzles due to its internal turbulence chamber creating smaller droplets and increasing driftable fines. The impact of nozzle selection on weed control was minimal and larger droplets at the rates and carrier volume used in this study could be used without compromising herbicide efficacy reducing drift potential. Adjuvants reduced the surface tension and contact angle of spray solutions; however, herbicide efficacy was only partially explained by the changes in these physical properties. Results emphasized the importance of better understanding the relationship among application variables and weed species. In addition, recommendations should be herbicide- and weed-specific in order to optimize herbicide applications and to maintain herbicide effectiveness.

Adviser: Greg R. Kruger