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Natural product-based herbicides could be the effective alternatives to synthetic chemical herbicides for eco-friendly weed management. This research, therefore, was conducted to identify the phytotoxic properties of <i>Parthenium hysterophorus</i> L., <i>Cleome rutidosperma</i> DC. and <i>Borreria alata</i> (Aubl.) DC. with a view to introducing them as a tool for natural herbicide development. The methanol extracts of these plants were examined on the germination and growth of <i>Zea mays</i> L., <i>Oryza sativa</i> L., <i>Abelmoschus esculentus</i> (L.) Moench and <i>Amaranthus gangeticus</i> L., <i>Oryza sativa</i> f. <i>Spontanea</i> Roshev. (Weedy rice), <i>Echinochloa colona</i> (L.) Link., <i>Euphorbia hirta</i> L., and <i>Ageratum conyzoides</i> L. under laboratory and glasshouse conditions. A complete randomized design (CRD) with five replications and randomized complete block design (RCBD) with four replications were laid out for laboratory and glasshouse experiments, respectively. In the laboratory experiment, three plant extracts of 0, 6.25, 12.5, 50, and 100 g L⁻¹ were tested on survival rate, hypocotyl, and radicle length of eight test plant species. No seed germination of <i>A. conzyoides</i>, <i>E. hirta</i>, and <i>A. gangeticus</i> were recorded when <i>P. hysterophorus</i> extract was applied at 50 g L⁻¹. <i>C. rutidosperma</i> had the same effect on those plants at 100 g L⁻¹. In the glasshouse, similar extracts and concentrations used in the laboratory experiments were sprayed on at the 2–3 leaf stage for grasses and 4–6 for the broadleaf species. Tested plants were less sensitive to <i>C. rutidosperma</i> and <i>B. alata</i> compared to <i>P. hysterophorus</i> extract. Among the weeds and crops, <i>A. conyzoides</i>, <i>E. hirta</i>, <i>A. esculentus</i> and <i>A. gangeticus</i> were mostly inhibited by <i>P. hysterophorus</i> extract at 100 g L⁻¹. Based on these results, <i>P. hysterophorus</i> was the most phytotoxic among the tested plant extracts and could be used for developing a new natural herbicide for green agriculture.