Efficacy of pre-emergence herbicides in managing weedy rice in wet-seeded rice

An experiment was conducted during 2023-2024 in a farmer’s field with a history of severe infestation of weedy rice located in Thrissur district, Kerala. The objective of the study was to identify effective pre-emergence herbicides for managing weedy rice and improving rice yield in wet-seeded rice. Twelve treatments were included, viz. oxyfluorfen 0.15 kg/ha just prior to sowing (0 DBS); oxyfluorfen 0.15 kg/ha at 10 days after seeding (DAS); butachlor at two doses 1.25 kg/ha and 0.625 kg/ha 7 DAS; pendimethalin 1.5 kg/ha 7 DAS; pretilachlor 0.75 kg/ha 7 DAS; pyrazosulfuron-ethyl 0.03 kg/ha 7 DAS; pretilachlor 30% + pyrazosulfuron-ethyl 0.75% (pretilachlor + pyrazosulfuron-ethyl) 0.62 kg/ha 7 DAS; pendimethalin 24% + penoxsulam 1% (pendimethalin + penoxsulam) 0.625 kg/ha 7 DAS; butachlor 38.8% + penoxsulam 0.97% (butachlor + penoxsulam) 0.82 kg/ha 7 DAS; unweeded control and weed-free check. Spraying oxyfluorfen 0.15 kg/ha just prior to sowing of pre-germinated rice seeds resulted in the highest weedy rice control efficiency (73%) at 30 DAS with grain yield reduction of only 8% compared to the 69% in unweeded control. The next best effective herbicides were oxyfluorfen 0.15 kg/ha 10 DAS and butachlor + penoxsulam 0.82 kg/ha 7 DAS, which registered 12 and 17% rice yield reduction, respectively. Phytotoxicity was observed with oxyfluorfen and butachlor, but the rice recovered within two weeks.