The loss of herbicide options due to resistance and lack of herbicide discovery has delivered the realisation that herbicides are a finite resource and weed control alternatives are desperately needed. In Australian conservation cropping the only available alternatives suited to routine use are the recently introduced harvest weed seed control (HWSC) and ever-present but undervalued, crop competition. Target-neighbour designed pot studies examined wheat (Triticum aestivum L.) competition effects on biomass and seed production of rigid ryegrass (Lolium rigidum Gaudin), wild radish (Raphanus raphanistrum L.), ripgut brome (Bromus diandrus Roth) and wild oat (Avena fatua L.). The influence of wheat competition on crop canopy distribution of weed biomass and seed production was also examined. At the current commercially targeted wheat density (120 plants m-2) weed biomass was reduced by 69, 73, 72, and 49% and seed production by 78, 78, 77, and 50% for L. rigidum, R. raphanistrum, B. diandrus, and A. fatua, respectively when compared with no competition. These results highlighted the importance of uniform wheat crop establishment in minimising the ongoing impact of weeds. Enhanced what competition (from 120 to 400 plants m-2) resulted in further smaller, but substantial, reductions in biomass (19, 13, 20 and 39%) and seed production (12, 13, 17 and 45%) for L. rigidum, R. raphanistrum, B. diandrus, and A. fatua, respectively. This enhanced competition also increased weed seed retention in the upper crop canopy (>40 cm) by 35 and 31% for L. rigidum and B. diandrus, but not for A. fatua and R. raphanistrum which was already >80% at the wheat density of 120 plants/m-2. Enhanced wheat crop competition then, has the dual effect of restricting the growth and development of L. rigidum, R. raphanistrum, B. diandrus, and A. fatua as well increasing the susceptibility of these weed species to HWSC.