Doctoral Dissertations

Date of Award

5-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant Sciences

Major Professor

Lawrence E. Steckel

Committee Members

Thomas C. Mueller, Scott D. Stewart, Jim Brosnan, Avat Shekoofa

Abstract

Junglerice has become a major weed in Tennessee and across the mid-south. Glyphosate resistance and dicamba antagonism has resulted in the reported control failures and rise in prevalence. Junglerice was the most prevalent weed escape in cotton and soybean fields across Tennessee from 2018 to 2020. In all, 13% of the junglerice accessions could no longer be effectively controlled with glyphosate. Due to poor in-crop control, it has been recommended to start clean when trying to control junglerice and other grasses. Therefore, research was conducted to determine the best burndown methods utilizing dicamba, glufosinate, or paraquat. A sequential application of glyphosate two weeks after the initial application was applied and provided the greatest control of junglerice regardless of burndown option. A dicamba + glyphosate, glufosinate + clethodim, or paraquat + clethodim application all provided the greatest control of junglerice (98, 90, and 90% respectively) amongst the different burndown options. On average, adding dicamba to the tank with glyphosate or clethodim reduced junglerice control by 19%. Labeled (TTI) nozzles reduced junglerice control an additional 8% and a drift reduction agent (DRA) reduced junglerice control an additional 16%. No antagonism differences were observed between dicamba and 2,4-D applications with glyphosate or clethodim. These results show that the addition of dicamba to glyphosate or clethodim applied with labeled nozzles and a DRA results in reduced junglerice control and should be avoided. Sequential treatments of glyphosate and/or clethodim preceding or following dicamba were examined. Overall, a glyphosate + clethodim application provided the most complete junglerice control regardless of timing. These data confirm that leaving dicamba out of the tank will mitigate antagonizing junglerice control. Glyphosate + clethodim applications in the future will aid in resistance management as well as the rise in glyphosate-resistant junglerice populations.

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