Phytotoxicity of Ageratum conyzoides L. ethyl acetate extract on Amaranthus spinosus L., Cyperus rotundus L. and Axonopus compressus L.

We evaluated the herbicidal activity of fractions recovered from the ethyl acetate leaf extract of Ageratum conyzoides L. on Amaranthus spinosus L., Cyperus rotundus L. and Axonopus compressus L. growth. The leaves of A. conyzoides were defatted with n-hexane and then extracted with ethyl acetate. Two subfractions A and B, were recovered after fractionation of the ethyl acetate extract by column chromatography. In pot assays, the ethyl acetate extract of 2-subfractions A and B were applied to A. spinosus, C. rotundus and A. compressus at concentrations of 2, 4, 6, 8 and 10 % and the herbicide (2,4-D at 0.686 kg a.i. ha-1) and distilled water applied as positive and negative controls, respectively. The subfractions showed phytotoxic activity 7-days after the start of the pot assay. Subfraction A at concentrations of 4 % or higher completely suppressed the growth of A. spinosus and that of A. compressus at 10 % concentration. Thus, subfraction B was less phytotoxic to weeds than subfraction A. The C. rotundus weed was less sensitive to both subfractions. GC-MS indicated the presence of caryophyllene (6.40 %), 2-propenoic acid, 3-(2-hydroxyphenyl)-, (E)- (15.35%), precosene II (23.33 %) and phytol (4.33 %) in subfraction A; and caryophyllene (9.61 %), 2-propenoic acid, 3-(2- hydroxyphenyl)-, (E)- (20.82 %), precocene I (3.27 %) and precocene II (29.78 %) in subfraction B. Our results showed that subfraction A had promising herbicidal effects on A. spinosus and A. compressus, while, subfraction B was herbicidal to A. spinosus. [ABSTRACT FROM AUTHOR]