Efficacy of post-emergence herbicides alone and as tank mixtures on weed control, growth and yield of roselle (Hibiscus sabdariffa)

A field experiment was conducted during rainy season of 2010–11 and 2011–12 at Regional Agricultural Research Station, Lam, Guntur, Andhra Pradesh to evaluate the efficacy of post-emergence herbicides alone and as tank mixtures on weed control, growth and fibre yield of roselle (Hibiscus sabdariffa). The post-emergence treatments applied at 20 days after sowing (DAS) include, fenoaxaprop-ethyl 56, quizalofop-ethyl 50, pyrithiobac 63 g/ha alone and tank mixtures of fenoxaprop-ethyl 56 + pyrithiobac 63 g/ha, quizalofop-ethyl 50 + pyrithiobac 63 g/ha in comparison with standard herbicide, pendimethalin 750 g/ha (pre-emergence), hand weeding at 20 and 40 DAS and weedy check. All the treatments were replicated thrice in a randomized block design. Results indicated that post-emergence (PoE) tank mix application of pyrithiobac 63 g/ha with quizalofop-ethyl 50 or fenoxaprop-ethyl 56 g/ha reduced weed growth at par with pre-emergence (PE) application of pendimethalin 750 g/ha both at 60 DAS and harvest. Post-emergence application of pyrithiobac 63 g/ha either alone or as tank mixture with fenoxaprop-ethyl 56, or quizalofop-ethyl 50 g/ha caused upto 40% injury to roselle crop at 14 days after application. All the weed control treatments significantly influenced crop growth and fibre yield. Among the weed control treatments, maximum fibre yield (2.36 t/ha) and benefit cost ratio (1.65) was obtained with pre-emergence application of pendimethalin 750 g/ha and was at par with alone PoE application of fenoxaprop-ethyl 56 g/ha (2.11 t/ha) and quizalofop-ethyl 50 g/ha (2.03 t/ha). None of the treatments could reach the level of hand weeding at 20 and 40 DAS, which significantly recorded the highest fibre yield (2.91 t/ha). Season long weed competition caused 46% reduction in fibre yield of roselle. It was concluded that the preemergence application of pendimethalin 750 g/ha was found to be effective and economical in controlling weeds in roselle.