Four weed species, eragrostis (Eragrostis tenella Roem. and Schult), cogongrass [Imperata cylindrica (L.) Beauv.], synedrella (Synedrella nodiflora Gaertn.) and tridax (Tridax procumbens L.) were planted at 5, 10, 15, 20 or 25 plants per pot. Competition affected shoot and root dry weights, height, and leaf number of all species and the reproductive characteristics of eragrostis and tridax. The interaction between species and plant density was also highly significant for shoot and root dry weights, height and leaf number. Individual plant height, shoot and root dry weights, leaf and node numbers, percent flowering per pot and the number of inflorescences produced decreased with increase in population density. This reduction was greatest in eragrostis followed by tridax. Synedrella (both disk and ray floret seeds) were least affected. There was no significant difference in the response of plants from disk floret seeds and ray floret seeds of synedrella.
