Date of Graduation

12-2021

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Norsworthy, Jason K.

Committee Member

Roberts, Trenton L.

Second Committee Member

Butts, Thomas R.

Third Committee Member

Gbur, Edward E. Jr.

Keywords

Agronomy; Herbicide; Rice; Tolerance; Weed Control

Abstract

Florpyrauxifen-benzyl (synthetic auxin, WSSA Group 4) is a postemergence, broad-spectrum herbicide labeled for use in Mid-South rice (Oryza sativa L.) production. Introduction of florpyrauxifen-benzyl to Arkansas rice production led to observations of varying levels of injury caused by the herbicide across cultivars and environments. Findings from previous research indicated hybrid long-grain rice and medium-grain rice were more susceptible to florpyrauxifen-benzyl and hypotheses were formed using this research regarding the impact of environmental conditions on the amount of injury observed. Concerns of yield loss, delay in maturity and loss of groundcover as well as questions regarding the ability of florpyrauxifen-benzyl to be applied with other herbicides that may cause injury led to the necessity for more research across cultivars and hybrids. Prior research also highlighted the benefits of using florpyrauxifen-benzyl in furrow-irrigated rice weed control programs to control problematic weed species such as Palmer amaranth (Amaranthus palmeri S. Wats). Florpyrauxifen-benzyl effectively controlled Palmer amaranth in a greenhouse study at lower-than-labeled rates and was found to be an effective alternative site-of-action for use in furrow-irrigated rice. Research conducted included experiments determining the tolerance of popular cultivars and hybrids to florpyrauxifen-benzyl with and without an application of benzobicyclon, isolation of multiple environmental and cultural variables to determine their effect on rice injury, and optimizing the rate and timing of florpyrauxifen-benzyl to best control Palmer amaranth in furrow-irrigated rice. Florpyrauxifen-benzyl reduced yield of rice hybrid XP753 by 17% following sequential applications at 30 g ae ha-1 and reduced groundcover of all hybrids tested. However, injury was not compounded by an application of benzobicyclon post-flood. Rice injury caused by florpyrauxifen-benzyl was most severe under 40% soil moisture or saturated conditions. Rice injury was more severe under low light conditions, high temperatures, and when the flood was introduced before three days and after six days following application. Single applications of florpyrauxifen-benzyl at 15 g ae ha-1 controlled Palmer amaranth as well as single applications of the herbicide at the labeled rate of 30 g ae ha-1. Florpyrauxifen-benzyl at 15 g ae ha-1 was as effective as 30 g ae ha-1 in controlling Palmer amaranth less than 10 cm in height. Sequential applications of florpyrauxifen-benzyl at 8 g ae ha-1 were as effective as sequential applications at 30 g ae ha-1. Based on these findings, injury caused by single applications of florpyrauxifen-benzyl at any rate appear superficial, although sequential applications of labeled rates can cause long-term effects on development and yield. Injury to rice can be reduced by timing an application based on soil moisture, solar radiation, temperature, and flood establishment date after application.

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