Effectiveness of Imazethapyr-Based Herbicide Programs for Weed Control in Drill-Seeded Imidazolinone-Resistant Rice Production in Northwest India

Abstract Drill-seeded rice (DSR) offers several agronomic and environmental advantages over conventional puddled transplanted rice (PTR), including labor and water savings, reduced cultivation costs, and lower greenhouse gas emissions. Despite these benefits, weed control remains a major bottleneck in the widespread adoption of DSR. Imidazolinone-resistant rice (IMI-rice), which allows the use of imidazolinone herbicides, has the potential to overcome weed control challenges in DSR and can therefore facilitate the transition from PTR to DSR. However, limited information exists on the effectiveness of IMI herbicide-based weed control programs in drill-seeded IMI-rice in northwestern India. Field experiments were conducted in Karnal, India, from 2020 through 2023 growing seasons to (1) evaluate the timing and rates of IMI herbicides for effective weed control in IMI-rice under DSR conditions, and (2) assess the potential carryover effects of IMI herbicides on succeeding crops. Results showed that sequential postemergence (POST) applications of imazethapyr—early-POST followed by ( fb ) late-POST at either 100 fb 150 or 125 fb 125 g ai ha -1 effectively reduced biomass by 83 to 100% for key weed species, including barnyardgrass, crowfootgrass, and Chinese sprangletop, compared to weedy check, and provided yields similar to weed-free treatment. These sequential POST treatments were consistently more effective than conventional herbicide program of oxadiargyl as preemergence (PRE) fb bispyribac-sodium as POST. Sequentially PRE fb POST applications of imazethapyr were relatively less effective in controlling weeds and minimizing yield losses compared to sequential POST applications. However, in the second and third years, oxadiargyl 90 g ai ha -1 as PRE fb imazethapyr 100 g ai ha -1 as POST achieved comparable weed control efficiency to the sequential POST applications of imazethapyr (125 fb 125 g ai ha -1 ). No visual phytotoxicity was observed on the succeeding crops of wheat, mustard, chickpea, lentil, and corn from any of the herbicide treatments applied in IMI-rice.