Evaluation of phytotoxic potential in Asteraceae plant extracts for biological control of <i>Echinochloa crus‐galli</i> and <i>Echinochloa colona</i>

This study evaluates the phytotoxic potential of methanolic extracts from six Asteraceae species: <i>Wedelia chinensis</i>, <i>Helianthus annuus</i>, <i>Cosmos bipinnatus</i>, <i>Tagetes erecta</i>, <i>Tithonia diversifolia</i>, <i>and Zinnia elegans</i>. The extracts were tested at concentrations of 0.03, 0.1, 0.3, and 1.0 g/mL to assess their inhibitory effects on the radicle and hypocotyl lengths of <i>Echinochloa crus-galli</i> and <i>Echinochloa colona</i>. The two most potent species, <i>C. bipinnatus</i> and <i>T. diversifolia</i>, were further evaluated using extracts from their roots, stems, and leaves. Among these, <i>C. bipinnatus</i> leaf extracts showed the most significant phytotoxicity and were tested at 20, 40, and 60 days of plant age. At 0.03 g/mL, <i>C. bipinnatus</i> extract inhibited the hypocotyl and radicle lengths of <i>E. colona</i> by 23.01% and 56.45%, and <i>E. crus-galli</i> by 8.5% and 36.35%, respectively. At 1.0 g/mL, the extract inhibited the hypocotyl lengths of <i>E. colona</i> and <i>E. crus-galli</i> by 97.54% and 88.15%, and the radicle lengths by 93.52% and 99.99%, respectively. The 60-day-old <i>C. bipinnatus</i> leaf extract exhibited the highest inhibitory effect, correlating with the identification of key allelochemicals such as cinnamic acid, caffeic acid, coumaric acid, ferulic acid, 2-4 dimethohydroxy benzoic acid, and salicylic acid. These findings suggest that the 60-day-old <i>C. bipinnatus</i> leaf extracts have strong potential for use in the biological control of these weed species, offering a promising avenue for the development of natural herbicides.