Doctoral Dissertations

Date of Award

5-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Tyson B. Raper

Committee Members

Thomas C. Mueller, Angela T. McClure, Christopher L. Main, Darrin M. Dodds

Abstract

Herbicide-resistant weed species have altered the challenges faced by Tennessee cotton (Gossypium hirsutum, L.) producers. While the weed control and environmental benefits of cover crops have been well-documented, the integration of cover crops into cotton production systems has presented management challenges. In-season broadcast postemergence weed control options are limited in cotton. Furthermore, off-target movement of 2,4-D and dicamba can result in additional management challenges if susceptible cotton is injured. Studies were conducted from 2018 to 2021 to evaluate: 1) cotton response to cover crop termination timings and methods; 2) postemergence weed control programs in cotton without the use of glyphosate; 3) the relationship between auxin injury, in-season reflectance data, and yield penalties; and 4) the effects of synthetic auxin exposure on yield components of cotton. Cover crop termination timings and methods impacted early season cotton growth, but yields were ultimately not affected. Postemergence control of weed species was generally greater with multiple POST applications compared to a single POST application but no herbicide program provided greater than 80% annual grass control 21 d after late-POST application. Auxin related injury and yield penalties may be better predicted following exposure during vegetative growth compared to exposure during reproductive growth. Exposure to 2,4-D caused more severe impacts to cotton than exposure to dicamba, but auxin application rate and timing impacted yield components and partitioning. Results from these studies will support a more sustainable production system through improved management of cover crops, selection of herbicide programs, and understanding of the scope and severity of off-target movement of 2,4-D and dicamba.

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