Texas Panicum (Urochloa texana (Buckley) R.D.Webster) Management in South Carolina Peanut (Arachis hypogaea L.) Production

Texas panicum (TP) is a persistent weed in South Carolina peanut fields, challenging growers with its season-long emergence and the limited availability of effective mid- to late-season herbicide options. Residual herbicides typically applied within 40 days of planting, fail to control late-emerging TP cohorts, making postemergence (POST) herbicides like clethodim and imazapic essential for managing this weed. Clethodim efficacy, however, depends on the TP growth stage and environmental conditions during application. To optimize control, this research evaluated clethodim applied at various TP growth stages (5 to 60 cm) and with different adjuvants. Clethodim was applied singly or in sequence, with a second application two weeks after the first for larger plants (15 to 60 cm). In another trial, clethodim was combined with Non-Ionic Surfactant (NIS), Crop Oil Concentrate (COC), Methylated Seed Oil (MSO), COC + Ammonium Sulfate (AMS), and MSO+AMS on 10-15 cm and 20-30 cm TP. Field results showed that sequential clethodim applications improved control by 12% compared to single applications, with the highest efficacy on smaller TP stages (5 to 15 cm). Clethodim combined with COC+AMS or MSO+AMS achieved over 90% control at 10-15 cm but was less effective on larger weeds. Greenhouse trials also indicated greater clethodim efficacy due to controlled conditions, confirming that TP is best managed at sizes less than 15 cm, especially when paired with COC or MSO+AMS. A second study assessed a rye cover crop combined with residual herbicides (s-metolachlor, pyroxasulfone, acetochlor, dimethenamid-p) and foliar POST treatments (imazapic, clethodim, paraquat, acifluorfen + bentazon). The rye covers reduced TP emergence, and herbicide programs incorporating imazapic with sequential clethodim applications maintained over 85% TP control at 75 days post-planting. TP populations were greater in 2024 than in 2023 reflecting warmer, drier conditions. Texas panicum competition negatively affected peanut yield, especially in the untreated plots where high TP densities hindered harvest. While all herbicide treatments significantly improved yields compared to untreated controls, a cost analysis revealed that the most effective combinations also ranked among the most economical for TP management. These findings highlight the effectiveness of integrated approaches, combining cover crops, selective residual herbicides, and targeted POST applications to successful TP control and improve peanut yields. Optimal TP management depends on proper timing, growth stage, and adjuvant choice to maximize clethodim efficacy.