Received: Dec 02, 2024 / Accepted: Mar 31, 2025 / Published: Mar 31, 2025
Weed management in rice cultivation faces increasing challenges due to herbicide resistance and environmental concerns, necessitating alternative, eco-friendly strategies. Among plant-based bioherbicides, Cosmos bipinnatus has emerged as a promising candidate due to its allelopathic potential. This study evaluated the efficacy of C. bipinnatus extracts in inhibiting key weed species, namely Echinochloa zcrus-galli, Leptochloa chinensis, Fimbristylis miliacea, and weedy rice (Oryza sativa f. spontanea). Bioassays demonstrated significant inhibition of radicle and coleoptile growth in these weeds, with stronger effects at higher concentrations. At 0.48 g mL⁻¹, inhibition reached 88% for E. crus-galli coleoptiles, 93% for its radicles, and 76% for L. chinensis coleoptiles. Notably, weedy rice, a major competitor in rice fields, was effectively suppressed, suggesting the potential of C. bipinnatus for integrated weed management. However, low extract concentrations (<0.06 g mL⁻¹) induced a hormesis effect, slightly promoting growth in some weeds and rice cultivars (OM380, OM5451, and OM18). Phytochemical analysis identified high phenolic (94.48 mg GAE g-1) and flavonoid (514.61 mg QE g-1) contents, particularly in leaves (45.93 mg GAE/g phenolic, 107.13 mg QE/g flavonoid) and flowers (63.89 mg GAE/g phenolic, 127.74 mg QE/g flavonoid), indicating their role as key inhibitory agents. These findings highlight C. bipinnatus as a viable biological solution for sustainable weed control, particularly against weedy rice. Further research is needed to optimize application strategies and minimize potential crop impacts, ensuring effective field applications while reducing reliance on synthetic herbicides in rice production systems.
