Herbicidal effects of n-hexane, ethyl acetate and methanol extracts of cogon grass (Imperata cylindica l.) and their phytotoxicity on spiny amaranth (Amaranthus spinosus l.) growth

Abstract

This research has the purpose of examining the activities of herbicidal effect of n-hexane, ethyl acetate and methanol extracts of cogon grass (Imperata cylindica L.) on spiny amaranth (Amaranthus spinosus L.) The rhizomes of I. cylindrica were extracted with n-hexane, ethyl acetate, and methanol, in that order. The extracts were tested on A. spinosus at concentrations of 5%, 10%, 15%, and 20%. We applied a synthetic herbicide at a concentration of 0.686 kg (2,4-D at 0.686 kg a.i. ha−1) for positive control, and for negative control, we used water without any chemicals (distilled water). The I. cylindrica extracts affects weed control, leaf area, root length, and shoot and root dry weight of A. spinosus. The application of 20 percent of n-hexane extract was the best treatment in terms of controlling A. spinosus (40.83%), but it was not different from other organic solvent treatments at various concentrations, in contrast to aquades (0.00%) and synthetic herbicides (100%). The n-hexane extract of I. cylindrica showed the strongest herbicide effect on A. spinosus after 28 DAA, while ethyl acetate and methanol showed only minimal herbicide effect. Gas Chromatography-mass spethroscopy (GC-MS) analysis showed that rhizome extracts of I. cylindrica contained 3 key compounds each as under : n-hexane extracts : [phthalic acid (43.30%), dibuthyl phthalate (29.75%), linoelaidic acid (5,93%)]; ethyl acetate extracts : [propanetriol acetate (31.73%), phthalic acid (5.69%), n-hexadecanoic acid (5.39%)]; methanol extracts : [acetic acid (52.95%), acetamide (21.86%), octaethylene glycol monododecyl (11.34%). The n-hexane extract proved promising to control A. spinosus