Abstract
A field experiment was conducted to investigate interference between pairs of 3 important grass weeds in Western Australia (Avena fatua, Bromus diandrus and Lolium rigidum) and to relate this to the impact of their mixtures on wheat (cv. Gamenya). Replacement series between the weed species were used, with wheat being present at a constant density in all plots. At the final harvest, relative yield totals for competition between the weeds did not differ significantly from unity, indicating a lack of niche differentiation. The impact of the weed mixtures on the crop did not differ from that of the monospecific weed populations, possibly as a result of the lack of niche differentiation.