Integrated weed management in direct-seeded rice: dynamics and economics

Abstract

Weeds are often the most severe problem in direct-seeded rice (Oryza sativa L.) (DSR), cause reductions in yield andprofitability. The traditional method of controlling rice weeds or manual weeding has several demerits as the practice isuneconomical and difficult. The effects of 10 different weed management practices were evaluated to identify the mosteffective and economical method of managing weeds in DSR in Nepal during the rainy season of 2010. Pendimethalinwas applied pre-emergence where 2,4-D, bispyribac sodium, and oxadiargyl were applied post-emergence alone orcombined with hand weeding. Sesbania (Sesbania aculeata Wild. Pers.) was co-cultured with rice and killed by withusing 2,4-D. Weed emergence, density, and biomass per unit area of 3 weed types: broadleaf, sedges, and grasses wereassessed during 20, 40, 60 days after seeding (DAS), and at harvest. Treatments were compared either to weedy check orweed-free control to determine weed control indices. A total of 42 weed species belonging to 27 genera and 11 familiesemerged across the growing season of rice. Most of the weeds were annual where broadleaf and sedges were dominantduring the first two months, and grasses were dominant under flooding. Weeds reduced the rice yield by more than 80% inweedy-check with respect to weed-free control. A sequential application of pendimethalin as pre-emergence andbispyribac-sodium postemergence herbicides followed by a hand weeding at 45 DAS provided up to 85% weed controlover weedy check than other weed control measures. However, that method found uneconomical when compared to thesame without hand weeding because of the high cost of manual labor. Pendimethalin was effective in controlling earlyflush of weeds and bispyribac efficiently controlled weeds even after flooding turned out to be a less expensive methodcontrolling in DSR. An integrated approach of weed management including both pre-emergence and post-emergenceherbicides can provide season-long weed control greater economic return.