Current status of herbicide-resistant weeds and their management in the rice-wheat cropping system of South Asia

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The rice-wheat cropping system is the backbone for food security in all South Asian countries on 13.5 million hectares, except in Sri Lanka, where the rice-rice cropping system is mainly followed. A large proportion of rice and wheat crops is produced as well as consumed in South Asia. Weeds are one of the major biotic factors constraining crop production, affecting crop production both quantitatively and qualitatively. Besides this, while shifting from traditional crop establishment methods (intensive tillage and puddling) to new ones (conservation agriculture practices), a shift in weed flora and its management is an emerging challenge. The use of herbicides is the most economic and effective weed control practice; and therefore, the use of herbicides for weed management is rapidly growing in the world, including South Asia. However, with injudicious use of herbicides, there is a trade-off in terms of resistance development, shifts in weed flora and ecological concerns. However, the evolution of resistance to commonly used herbicides in targeted weed species is the most serious among them. There is diversity of weed species in the rice-wheat cropping system, which has already evolved resistance to a few herbicides in India, Pakistan, and Sri Lanka. Therefore, a proper understanding of herbicide resistance, its evolution, and mechanism is essential. Manual weeding is either not possible, or uneconomical and ineffective due to rising labor shortages and wages. Under such situations, there is an increasing need to integrate and implement different weed management practices, including the sensible use of herbicides along with other control measures, such as adjusting the sowing time, use of weed-competitive cultivars, altering crop establishment methods, tillage practices, crop rotations, optimum use of inputs, in-season crop management practices, etc., to tackle the problem of herbicide resistance.