Date of Graduation

5-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Norsworthy, Jason K.

Committee Member

Norman, Richard J.

Second Committee Member

Scott, Robert C.

Third Committee Member

Gbur, Edward E. Jr.

Fourth Committee Member

Faske, Travis

Keywords

Biological sciences; Barnyardgrass; Herbicide; Rice

Abstract

Barnyardgrass remains one of the most difficult weeds to manage in rice. As herbicide resistance in this species, as well as others, continues to increase new control options are needed. Dow AgroSciences recently discovered and is developing a new herbicide for rice which is the primary focus of this research. Experiments were conducted to characterize this new herbicide for its use and effectiveness in midsouthern U.S. rice systems. The research conducted herein covers various aspects of herbicide characterization including: barnyardgrass dose response, accession testing, spectrum of control and tank-mix capability, application optimization, soil carryover and plant back determination, drift onto susceptible crops, drift onto reproductive soybean and its impact on the subsequent offspring, and radiolabeled isotope absorption, translocation, and metabolism. In a dose-response experiment, susceptible-, acetolactate synthase (ALS)-, propanil-, and quinclorac-resistant barnyardgrass biotypes ED90 values for percent control, plant height, and biomass reductions of all resistant biotypes fell within the anticipated labeled rate of 30 g ha-1. Based on these results, quinclorac-resistant barnyardgrass as well as other resistant biotypes can be controlled with florpyrauxifen-benzyl, even with quinclorac having a similar mechanism of action. Florpyrauxifen-beznyl appeared to have significant tank-mix flexibility with other commonly applied rice herbicides. Increasing the rate of methylated seed oil (MSO) improved weed control with both formulations of florpyraixifen-benzyl. In addition, flooding shortly after application enhanced barnyardgrass and yellow nutsedge control. Plant back study results support a relatively short replant interval for soybean (≤2 months) after florpyrauxifen-benzyl application to rice. Additionally, it is believed that florpyrauxifen-benzyl will only present slight risks for off-target movement to vegetative soybean. However, high drift rates (1/20x) of florpyrauxifen-benzyl during R1 to R4 significantly reduced soybean plant height >25% and yield. Germination, stand, plant height, and yield of the progeny from dicamba- and florpyrauxifen-benzyl-treated soybean plants were significantly affected. Furthermore, research on radiolabeled florpyrauxifen-benzyl suggests that for barnyardgrass, hemp sesbania, and yellow nutsedge soil moisture can play a significant role in absorption, translocation, and metabolism. These results indicate this new herbicide will provide control of numerous problematic weed species, but users will need to be mindful of soybean sensitivity.

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