Crop growth rate and weed competition were studied in New South Wales, Australia during 2002 using reflectance sensors. Seeds of wheat cv. Sunstate, chickpea cv. Howzat, faba bean cv. Fiord and rape cv. Oscar were sown at 40, 70, 100 and 3 kg/ha, respectively. Two reflectance sensors mounted on a small tractor were used to collect data across each plot every two weeks (45-129 days after sowing). Wheat recorded the greatest biomass, yield and water consumption, whereas chickpea recorded the highest harvest index and lowest water consumption. The rate of crop development was greatest in wheat and lowest in chickpea. The number of days required to produce 1000 kg/ha of shoot dry matter was 92, 100, 102 and 11 days after sowing for wheat, faba bean, rape and chickpea, respectively. Reflectance measurements were also used to evaluate the potential of wheat, triticale and barley as 'mimic weeds' against wild oat [ Avena fatua] in chickpea. Reflectance estimates were made at 51, 62, 84, 100 and 120 days after sowing. The 'mimic weeds' established faster than wild oat. The density of wild oat was lower than that of the mimic weeds, although none of the weeds achieved the target density of 81 weeds/m 2. The similar linear relationships with regard to the effects of weed biomass on crop yield for wild oat and 'mimic weeds' indicated that the latter can be used in weed studies instead of the actual weed. At low densities, wheat and barley were the most competitive. Triticale and wild oat exhibited similar competitive ability.
