Date of Graduation

5-2022

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

Rice; Oryza sativa; Arkansas; Rice producers; Rice hectares

Abstract

Controlling weedy rice postemergence is challenging for rice producers in the United States because of the lack of herbicide options. Weedy rice is genetically similar to cultivated rice, thus making it difficult to control with mid-season postemergence herbicide applications without also damaging the crop. Hence, there is a need for a new effective postemergence weedy rice control herbicide. Findings from this research indicate that the use of benzobicyclon in current standard quizalofop- and imidazolinone-resistant rice herbicide programs provides tremendous utility for Midsouth rice producers. In both of these production systems, the addition of benzobicyclon to the respective standard herbicide programs resulted in comparable or improved weedy rice control compared to the standard program alone. Additionally, minimal injury was observed from treatments containing the current standard herbicide program followed by the postflood application of benzobicyclon.

To validate that benzobicyclon is a viable weed control option for rice growers, research was conducted to evaluate varietal tolerances of commonly grown rice cultivars to the application of benzobicyclon. Plants are typically more sensitive to herbicides when they are small, and that sensitivity tends to decrease as the plant produces more vegetative growth. In the first year of this research, 4-leaf and tillering rice exhibited sufficient tolerance to benzobicyclon, whereas 2-leaf rice did not. However, in the second year, all treatments, or combinations of application timing/rice cultivar were not injurious to rice, which was partially attributed to loss of the herbicide from the field as a result of a rainfall event. Some rice cultivars, depending on genealogical lineage, are extremely susceptible to benzobicyclon and other 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides. More specifically, japonica-type rice cultivars show much better crop safety to benzobicyclon than indica-type or japonica- x indica-type. In this research, the indica-type rice cultivar ‘Rondo’ was severely injured, regardless of benzobicyclon application timing.

Since benzobicyclon is a pro-herbicide, it does not directly inhibit HPPD enzymes in plants. Rather, benzobicyclon must undergo (in the presence of water) a non-enzymatic hydrolytic reaction to be converted to the potent and phytotoxic compound benzobicyclon hydrolysate. Therefore, since benzobicyclon requires the presence of water to be phyto-active, it must be applied postflood, and applications will likely occur in proximity to actively growing soybean. In this research, treatments containing benzobicyclon alone, regardless of reduced rate applied, injured soybean ≤8% at 14 days after treatment, indicating that benzobicyclon can be safely applied to rice near soybean with minimal risk for injury to the adjacent crop.

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