Herbicidal effects of n-hexane, ethyl acetate and methanol extracts of billygoat weed (Ageratum conyzoides l.) leaveson amaranthus spinosus l. growth

Abstract

The herbicidal activity of Ageratum conyzoides L. extracts was evaluated on the weed Amaranthus spinosus L. The leaves of A. conyzoides were sequentially extracted with n-hexane, ethyl acetate and methanol. In pot culture, these extracts were applied to A. spinosus plants at concentrations of 5 %-20 %. Positive and negative controls were 2,4-D (2,4-dichlorophenoxyacetic acid) applied at 0.686 kg a.i.ha-1 and distilled water. The A. conyzoides extracts had variable effects on leaf area, and shoot and root dry weight and weed control (%) of A. spinosus. The ethyl acetate extract was most inhibitory than n-hexane extract, while the methanol extract had no effect. Twenty one days after application, the applied ethyl acetate extract at 20 % concentration completely controlled the A. spinosus similar to 2,4-D. Main constituents identified by GC-MS in ethyl acetate extract were: 1,8-cineole (3.90 %), caryophyllene (25.47 %), precocene II (59.22 %), and 2,6,10,14,18,22-tetracosahexaene (5 %). In n-hexane extract were: precocene II (16.63 %), neophytadiene (14.94 %), phytol (8.24 %), and α-Methyl linolenate (14.13 %) and in the methanol extract were: 1,8-cineole (3.78 %), precocene II (9.16 %), neophytadiene (20.6 %), phytol (14.12 %) and 9,12,15-octadecatrienoic acid methyl ester (9.36 %). The ethyl acetate extract proved promising to control the weed A. spinosus.