Weed dynamics and management strategies for dry direct-seeded rice in South Asia: a review

Background Weeds are the number one pest of agricultural production systems and are a major constraint to the success of dry direct-seeded rice (DDSR). Main text In this paper, the weed dynamics and management practices of DDSR are critically reviewed to minimize their influence on rice-based cropping systems in South Asia (SA). The yield losses due to uncontrolled weeds in the DDSR can reach 100%. Even when farmers manage weeds, yield losses generally range from 20 to 30% in SA. The dominant weed species reported in DDSR systems are Cyperus rotundus L., Echinochloa colona (L.) Link, Cynodon dactylon (L.) Pers., Digitaria ciliaris (Retz.) Koel., Leptochloa chinensis (L.) Nees., Alternenthera sessilis L., etc. Shifting of weed species was reported from SA studies when farmers practiced DDSR because of changes from flooding to aerobic soil conditions and changes in weed management strategies. Manual weeding is popular in SA, but relying solely on it is not economically viable in DDSR systems. Therefore, available integrated approaches, such as preventive, cultural, mechanical, and chemical measures, are needed. Herbicides are considered essential in DDSR systems because they help prevent early flushes of weeds and subsequent growth. Effective herbicide strategies include the use of preemergence applications of pendimethalin, followed by postemergence treatments with herbicides such as bispyribac-sodium or penoxsulam, and then manual weeding as needed. However, the increasing reliance on herbicides has led to the emergence of herbicide resistance, particularly in species such as Echinochloa spp. and weedy rice, which poses a significant threat to sustainable weed control. Limited information was found on weed resistance issues in SA. Conclusion The future perspective on weed management in DDSR systems emphasizes the need for continued research collaboration and stakeholder involvement, farmer training, and the development of the capacity of researchers and extension workers.