Date of Graduation

12-2023

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Thomas R. Butts

Committee Member

Norsworthy, Jason K.

Second Committee Member

Bateman, Nick R.

Third Committee Member

Poncet, Aurelie M.

Keywords

Barnyardgrass, Rice, Row width

Abstract

Weed control is a major problem that rice (Oryza sativa L.) producers face in the Mid-south every growing season. Restricted use of some rice herbicides has also highlighted the need for more research to be conducted on cultural weed control strategies and application technologies in rice. The aim of these studies was to evaluate rice weed control using various rice row widths, bed widths (irrigation-furrow spacing), rice cultivar selection, and nozzle type selection. Three field experiments were conducted in 2021 and 2022 across four sites at Lonoke, AR, Pine Tree, AR, Rohwer, AR, and Stoneville, MS. In experiment one, as row width increased, barnyardgrass [Echinochloa crus-galli (L.) Beauv.] density increased. Barnyardgrass density increased by 120% in the 38-cm row width compared to the narrowest 13-cm row width at the preflood rice stage. Rice canopy coverage was reduced in the wider row widths early-season allowing increased barnyardgrass escapes. The hybrid cultivars resulted in a lower barnyardgrass density at the preharvest stage and higher grain yields than the inbred cultivars. Row width did not affect rice yield, indicating wider row widths could be feasible agronomically, but additional weed management efforts would be needed. The standard row width (19-cm) and hybrid cultivars would be recommended because growers would not need to purchase new equipment while maintaining weed management efforts and grain yields. In experiment two, similar results were observed that as rice row width increased, barnyardgrass density increased and rice canopy coverage decreased. The smallest droplet size-producing nozzle (XR) provided greater weed control throughout the study but is more prone to drift. Dual-fan nozzles (AITTJ60 and TTI60) had variable weed control impacts; however, they did have increased deposits on water-sensitive cards compared to single-fan counterparts (AIXR and TTI) indicating there may be potential for dual-fan nozzles to enhance weed control efforts. In conclusion, a narrower row width (e.g., 19-cm or less) and a smaller droplet size producing nozzle (XR), when drift is not a concern, are the most optimal for barnyardgrass control in a flooded rice system. In experiment three, any of the bed widths tested (76-, 97-, and 152-cm) could be used for maintaining effective weed control and yield in a furrow-irrigated rice system. The widest bed width of 152 cm had a slight increase in barnyardgrass density in the early rice life cycle but by harvest, panicle density did not differ from the narrower bed widths. Conversely, a decrease in barnyardgrass seed production was observed as the bed width increased. Similar rice canopy coverage and yields occurred between all three bed widths. The 13-cm row width had the lowest preflood barnyardgrass density, preharvest panicle count, and barnyardgrass seed production. No effect of row width was observed on rice canopy coverage; however, the 13-cm row width produced the greatest rice yield. The 13-cm row width may be the optimum row width option in furrow-irrigated rice paired with the 152-cm bed width to optimize weed management, particularly barnyardgrass seed production, while maintaining rice growth and yield.

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