Abstract
This study aimed to evaluate the herbicidal activity of ethyl acetate leaf extract of Ageratum conyzoides L. at different subfractions on Amaranthus spinosus L. The leaves of A. conyzoides were sequentially extracted with n-hexane and ethyl acetate respectively and fractionated by chromatography column. The extracts were applied to A. spinosus in pot assays at a concentration of 5%, 10% and 15%. We applied A synthetic herbicide (2,4-D at 0.686 kg a.i. ha−1) for positive control and distilled water for negative control. The A. conyzoides extracts strongly differed in their effect on weed control, shoot and root dry weight and root length of A. spinosus. The most inhibition on A. spinosus growth caused by application of ethyl acetate of A. conyzoides extracts subfraction A by 10% concentration can cause 100% destruction and subfraction B were 95% which both of them cause strongest death on A. spinosus compared with synthetic herbicide (2, 4-D) (23.33%) at 1 Day After Application, while subfraction C and D were not effective. Main constituents identified by GC-MS in subfraction A extract were tetradecanoic acid, ethyl ester (10.26%), precocene II (9.39%), octadecanal (8.23%), 9,12,15-octatadecatrienoic, methyl ester (7.32%), 10-heneicosene (c,t) (5.19%) and neophytadiene (5.09%); in subfraction B were 1-octadecyne (38.57%), phytol (11.24%), di-tert-utylphosphine-d (5.17%) and 1-hexadecine (4.08%); in subfraction C were allobarbital (8.53%), octadecanal (12.69%), and bannamurpanin (26.01%) and octadecanal (30.52%), bannamurpanin (24.06%), 1,8-cineole (15.75%), trans-dodec-5enal (12.28%) and phytol (8.26%) in subfraction D. The ethyl acetate extract subfraction A and B concentration 10% proved the promising control agent against A. spinosus.
Highlights
The ethyl acetate A. conyzoides subfraction A extract concentration of 10% gave a complete effect caused A. spinosus mortality (100%), followed by the application of A. conyzoides ethyl acetate subfraction B extract with 10% concentration (95% inhibition with severe influence) at 1 days after application (DAA) (Figure 2)
C and D concentrations of 10% did not cause weed mortality (10% inhibition and 0%, respectively) at 21 DAA, had a similar percentage of weed control with distilled water application (0%))
Dry shoot and root weights and root length indicated that the ethyl acetate extract of A. conyzoides subfraction A had the strongest post-emergence herbicidal effects on A. spinosus (100% inhibition) followed by ethyl acetate A. conyzoides subfraction B (95% inhibition), while ethyl acetate A. conyzoides subfraction C dan D
Summary
Continuous application of such synthetic chemical herbicide tends to create a negative impact on soil [2], weeds resistance to herbicide [3,4], poison to non-targeted organisms, disturb ecology as a whole and leave chemical residues on the environment [5]. It requires effective and efficient control as alternative ways which are environmentally safe. Results of study about allelopathic screening of five perennials plants species (Pinus merkusii Jungh. et de Vriese, Acacia mangium Willd., Jatropha curcas L., Tectona grandis L.f., Terminalia catappa L.) and weed species (Imperata cylindrica L., Ageratum conyzoides L., Cyperus rotundus L., Chromolaena odorata L. and Axonopus compressus (Swartz)
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