Synergistic Effects of Yellow Cosmos (Cosmos sulphureus Cav.) Extracts and Adjuvants for Rice Weed Management

Ho Le Thi*, Nguyen Gia Huy, Nguyen Huynh Kha Han, Nguyen Hoang Thien Phuc, Vi Tuan Kiet, Nguyen Duy Khanh

Keywords:

Yellow Cosmos, Cosmos sulphureus extracts, Adjuvants, Bioherbicide efficacy, Rice weed management, Sustainable agriculture

Abstract:

This study investigated the weed control efficacy of Yellow Cosmos (Cosmos sulphureus Cav.) leaf extract (SNV) in combination with adhesive adjuvants, including sodium lauryl sulphate (SLS), lauryl alkyl sulfonate (LAS), carboxymethyl cellulose (CMC), and esterified vegetable oil (EVO), under greenhouse conditions. Eleven foliar-applied treatments were tested in pot experiments against three dominant rice weeds (i.e. barnyard grass [Echinochloa crus-galli], red sprangletop [Leptochloa chinensis] and grasslike fimbry [Fimbristylis miliacea], grown in mixed culture with the rice cultivar, OM5451. Our results revealed that SNV combined with SLS or LAS markedly enhanced weed suppression, reducing the height of L. chinensis by up to 76.2% and F. miliacea by 77.2%, while minimising adverse effects on rice growth (<3.5%). Fresh biomass of E. crus-galli declined to 4.8% with SNV+SLS, compared with 6.0% in the SNV alone treatments. These findings highlight that the integration of suitable adjuvants, particularly SLS and LAS, can significantly improve the performance of bioactive plant extracts while maintaining crop safety, offering a promising approach for sustainable rice weed management.