Date of Graduation
5-2025
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
Butts, Thomas R.
Second Committee Member
Roberts, Trenton L.
Third Committee Member
Fernandes, Samuel B.
Keywords
Palmer amaranth; rice; fluridone; furrow-irrigation
Abstract
The increasing pressure of Palmer amaranth [Amaranthus palmeri (S.) Watson] in rice (Oryza sativa L.) fields demands new chemical control options to manage this weed. The recent labeling of fluridone on this crop from the three-leaf rice stage offers an additional residual herbicide for battling Palmer amaranth; however, research is needed to evaluate its effectiveness and rice tolerance. Field experiments were conducted to evaluate Palmer amaranth control and rice tolerance to fluridone across different locations in Arkansas in 2022, 2023, and 2024. Preemergence (PRE) applications of fluridone at 168 g ai ha⁻1; (1× label rate) and 336 g ai ha⁻1; (2× label rate) caused severe crop injury to several rice cultivars, leading to grain yield reductions of up to 49% in eight of the most commonly grown cultivars in Arkansas in a flooded rice production. The cultivar DG263L exhibited injury levels of up to 50% and 32% following PRE and three-leaf applications at the 1× rate, respectively, with yield reductions observed at both application timings, indicating low tolerance to fluridone. When comparing ten application timings from 20 days preplant to postflood applications, the treatments near planting caused the greatest injury to rice grown in a delayed-flood system and the applications at PRE and delayed-preemergence decreased rice grain yield. Therefore, fluridone should not be used at early rice stages, as indicated by the label. Additionally, fluridone applied in mixture with standard rice herbicides at the three-leaf growth stage increased injury by up to 8 percentage points compared to the standard herbicide alone. No yield or groundcover reductions were detected with the addition of fluridone, indicating this herbicide can be applied with other rice herbicides for improved weed control while posing minimal risk to the crop. In a furrow-irrigated rice system, PRE applications of fluridone at the 2× label rate caused 8% to 34% injury; however, no yield reduction was observed. In the same system, fluridone at the 1× and 2× label rates reduced Palmer amaranth density by at least 65% and 88%, respectively, four weeks after treatment compared to the nontreated control. Furthermore, the addition of florpyrauxifen-benzyl postemergence following a PRE application of fluridone at 0.5×, 1×, or 2× label rates reduced Palmer amaranth escapes and decreased seed production by at least 94% compared to fluridone alone at rice maturity. Although florpyrauxifen-benzyl resulted in lower weed densities at the end of the season, the presence of remaining weeds likely contributed to lower rice grain yield compared to treatments where no weeds were present. Thus, sequential applications of other effective herbicides are necessary for season-long Palmer amaranth management.
Citation
de Carvalho Rocha Souza, M. (2025). Evaluation of Fluridone in Rice. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/5670
