Background: Leptochloa chinensis is a major weed in rice that can significantly affect rice due to its competitive nature and difficulty to control, even with herbicides such as metamifop. The use of surfactants can enhance the efficacy of metamifop against L. chinensis. Objectives: A screenhouse experiment was conducted to evaluate the efficacy of metamifop applied with nonionic surfactant (NIS) for the control of L. chinensis and the crop response of rice. Methods: L. chinensis and rice (NSIC Rc 222) plants were treated with 37.5, 56.25, and 75 g ai ha-1 metamifop in combination with 0.05, 0.1, 0.25, 0.5, and 1% v/v NIS when plants were 10 to 13 cm in height. Results: Results showed that the addition of NIS significantly enhanced metamifop activity against L. chinensis, increasing control by 24-40% compared to the herbicide alone. However, phytotoxicity symptoms were observed with injury levels increasing at higher herbicide rates (up to 12% at 75 g ai ha-1) and higher NIS concentrations (up to 13% at 1% v/v NIS). However, symptoms were transient and rice plants exhibited near-complete recovery by 21-28 days after treatment (DAT). Biomass reductions were minimal and rice demonstrated compensatory growth, recovering from early stress regardless of treatment. Conclusion: These findings indicate that the efficacy of metamifop against L. chinensis can be substantially improved by the addition of NIS, particularly at 0.1-0.25% v/v.
Abit et al. (Wed,) studied this question.