Use of a Capsule Suspension Formulation of S-metolachlor in Fenclorim-Treated Rice

Authors

Jason K. Norsworthy, University of Arkansas, FayettevilleFollow
Samuel C. Noe, University of Arkansas, FayettevilleFollow
Thomas R. Butts, University of Arkansas System Division of AgricultureFollow
Trenton L. Roberts, University of Arkansas, FayettevilleFollow

Document Type

Article

Publication Date

12-2024

Keywords

Fenclorim; S-metolachlor; rice, Oryza sativa L.; Crop tolerance; delayed preemergence; 1-leaf; silt loam

Abstract

As herbicide resistance continues to render commonly used rice herbicides ineffective, alternative sites of action are paramount to maintaining yield and producer profitability. Combining a slow-release formulation and a fenclorim seed treatment might allow the safe use of S-metolachlor in rice. Experiments were initiated in 2022 and 2023 near Colt, AR, on a silt loam soil to evaluate crop safety using a capsule suspension (CS) formulation of S-metolachlor and a fenclorim seed treatment in rice. The first experiment assessed the tolerance of two cultivars (‘Diamond’ and ‘DG263L’) to three rates (0.42, 0.84, and 1.68 kg ai ha⁻¹) of a CS S-metolachlor at a delayed preemergence (DPRE) application timing in conjunction with a fenclorim seed treatment. The second experiment evaluated a 1- to 2-leaf (EPOST) application of a CS S-metolachlor at 0.56 and 1.12 kg ai ha⁻¹ to fenclorim-treated rice. Fenclorim reduced injury and partially protected rice yield when S-metolachlor was applied DPRE at 1.68 kg ai ha⁻¹ in both years. However, in one year, under adverse conditions, rice yields were only 65% and 66% of the nontreated control for fenclorim-treated ‘Diamond’ and ‘DG263L’, respectively. An EPOST application of S-metolachlor at 1.12 kg ai ha⁻¹ resulted in 44% to 51% visible injury 35 d after treatment. Relative rice yields were 88% and 89% of the nontreated weed-free treatment in 2022 and 2023, respectively. Fenclorim provided enhanced crop safety at both the 0.84 and 1.68 kg ai ha⁻¹ rates of S-metolachlor. However, the potential for reduced yield can arise when unfavorable conditions occur soon after application. An EPOST application timing of CS S-metolachlor at 0.56 kg ai ha⁻¹ may be a viable option in rice, but 1.12 kg ai ha⁻¹ is too high on a silt loam soil, resulting in significant rice injury.

Citation

Norsworthy, J. K., Noe, S. C., Butts, T. R., & Roberts, T. L. (2024). Use of a Capsule Suspension Formulation of S-metolachlor in Fenclorim-Treated Rice. Weed Technology, 39, e6. https://doi.org/10.1017/wet.2024.96

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