Title

Documentation and Control of Acetolactate Synthase-Resistant Barnyardgrass (Echinochloa Crus-galli) in Arkansas Rice

Date of Graduation

12-2012

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Jason K. Norsworthy

Committee Member

Lawrence R. Oliver

Second Committee Member

Robert C. Scott

Third Committee Member

Richard Norman

Fourth Committee Member

Edward G. Gbur

Abstract

Barnyardgrass, the most problematic grass weed of Arkansas rice, was found resistant to propanil in 1990, and since then, it has evolved resistance to quinclorac and clomazone. Barnyardgrass is now believed to have evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides. The goal of this research was to confirm and determine the level of resistance of the putative resistant biotype to the ALS-inhibiting herbicides imazethapyr, bispyribac, and penoxsulam and to develop herbicide programs for controlling ALS-, propanil-, quinclorac-, and clomazone-resistant barnyardgrass. The lethal dose needed to kill 50% of the putative ALS-resistant plants was higher than that of the susceptible biotype and greater than the field use rate of imazethapyr, bispyribac, and penoxsulam, indicating cross-resistance. The ALS-resistant biotype was also resistant to imazethapyr, propanil (photosystem II-inhibitor), and quinclorac (synthetic auxin). In the field, two applications of imazethapyr alone failed to control the ALS-resistant biotype (<43%); however, when imazethapyr was applied early postemergence followed by imazethapyr + fenoxaprop preflood, barnyardgrass control improved. When imazethapyr was applied twice following preemergence or delayed preemergence application of other herbicides, acceptable control was obtained with or without the addition of fenoxaprop preflood. Herbicide programs were developed that effectively controlled multiple-resistant biotypes, and some single-application programs consisting of three or four herbicides were as effective as multiple applications in providing season-long control.

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