Weed management in wet direct-seeded rice (Oryza sativa L.): Issues and opportunities

Wet direct-seeded rice (WDSR) is a method of direct seeding which involves sowing pre-germinated seeds on or into puddled soil. In the wake of water and labor shortages, this method is an effective alternative to the puddled transplanted rice system. Weed infestation has emerged as the major constraint for the success of WDSR as weeds cause more yield loss in this system compared to the transplanting system. The simultaneous emergence of weeds and rice seedlings due to lack of ponding results in heavy weed infestation under WDSR. This has necessitated the use of herbicides for effective and cost-efficient weed control. Pre-emergence (PRE) herbicides, such as butachlor, pretilachlor, oxyfluorfen, pendimethalin; post-emergence (POST) herbicides, such as pyrazosulfuron-ethyl, bensulfuron methyl, bispyribac-sodium, propyrisulfuron, penoxsulam plus cyhalofop-butyl, bispyribac+(chlorimuron plus metsulfuron), bensulfuron methyl plus pretilachlor, pretilachlor plus pyribenzoxim; and pre-plant (PPI) herbicides, such as flufenacet and dimethenamid, have been found to be the most effective herbicides in WDSR when either used alone or as a sequential application of PRE and POST herbicide. However, the indiscriminate use of herbicides has caused the development of herbicide resistance in weeds. Shifts in weed flora and the occurrence of weedy rice are other major challenges associated with WDSR. This paper outlines the currently available weed management options for key production areas of WDSR and enumerates associated challenges and constraints. Recent developments, potential approaches, and cutting-edge techniques have been enlisted along with the identification of future research requirements for weed management in WDSR-based cropping systems. Preventive, physical (manual and mechanical weeding), biological (allelopathy), and cultural (stale seedbed, intercropping, water management, weed competitive cultivar, mulching, manipulation of crop geometry and seeding rate, and fertilization) weed control practices were found to be of vital importance for weed management in WDSR systems. Ultimately, the integration of multiple tactics for a long-term and sustainable weed management program in WDSR is required. Innovative techniques such as nano-herbicides, harvest weed seed control, remote sensing, and precision equipment offer advantageous opportunities for strengthening integrated weed management programs in WDSR. While WDSR is conducive to heavy weed infestation, there remains significant potential to expand the effective implementation of weed management strategies for the overall enhancement of crop yield.