Comparative efficacy of herbicides against rock bulrush Schoenoplectus juncoides (Roxb.) Palla in wet-seeded rice

Field experiment was conducted at the College of Agriculture, Vellayani during 2017–2018 to assess the efficacies of pre-emergence, early post-emergence and post-emergence herbicides for managing rock bulrush Schoenoplectus juncoides (Roxb.) Palla, an emerging sedge weed in the lowland paddy fields of Kerala. A pre-emergence spray of bensulfuron-methyl + pretilachlor 60+ 600 g/ha at 4–7 days after sowing (DAS) was effective till 30 DAS with 93.3% reduction in weed count. At 45 and 60 DAS, lower weed density (2.09 and 3.15 no./m², respectively) and weed dry weight (0.13 and 1.83 g/m², respectively) were recorded for ethoxysulfuron 15 g/ha at 15 DAS fb HW at 40 DAS. Higher weed control efficiencies of 99.8% and 98.1% were obtained in plots treated with ethoxysulfuron 15 g/ha at 15 DAS fb HW at 40 DAS during critical stages of crop-weed competition (45 and 30DAS). Penoxsulam 22.5 g/ha at 15 DAS and ethoxysulfuron 15 g/ha at 15 DAS both fb HW at 40 DAS were on a par at 45 and 60 DAS in terms of weed control efficiency (99.1% and 97.9%, respectively. The weed removal of N, P and K (8.61, 3.13 and 10.95 kg/ha, respectively) were also lower with ethoxysulfuron 15 g/ha at 15 DAS fb HW at 40 DAS. The study revealed that rock bulrush could be effectively controlled by ethoxysulfuron 15 g/ha or penoxsulam 22.5 g/ha both at 15 DAS fb HW at 40 DAS.