This research objective was to examine the effect of herbicide, genotype, population and sowing date on crop yield and weed growth in Pisum sativum. In 2007/08, cyanazine treated peas had a mean seed yield of 508 g m-2 , 19% more than in unsprayed plots. There was a significant sowing date by pea genotype interaction which showed that in the August sowing genotype had no effect on seed yield. However, in September Pro 7035 yielded 559 g m-2 , which was 40% more than Midichi. By the October sowing, it was 87% more. There was a distinct variation in weed spectrum, over time. It can be concluded that fully leafed peas and semi-leafless can be sown at similar plant populations and give similar yields under weed free conditions and that increased pea sowing rates increased total dry matter and seed yield in weedy environments. Fully leafed peas yielded more than semi-leafless peas when both were late sown. Increased pea sowing rate improved weed suppression.

Two trials were conducted on a Templeton silt loam soil at Lincoln University, New Zealand (43 o 38' S, 172 o 28' E.) in 2007/08. The aim was to compare the competitive ability of different pea canopy architectures as influenced by genotype, population, sowing date and their interaction as a means of low input weed control strategy. The first experiment had three sowing dates, two pea genotypes and two herbicide treatments. Experiment 2 treatments were a factorial combination of four pea populations and three sown artificial weed populations. A significant sowing date x pea genotype interaction showed that in the August sowing genotype had no effect on seed yield. However, in September sown plots Pro 7035 yielded 559 g m -2 , which was 40% more than Midichi, and in the October sowing, the difference was 87% more. Herbicide-sprayed peas produced 19% more seed (508 g m -2 ) than the unsprayed plants. When no weeds were sown, the highest pea total dry matter (TDM) of 1,129 g m -2 occurred at 200 plants m -2 . This was more than twice (513 g m -2 ) the yield of the lowest population (50 plants m -2 ). There was distinct variation in the weed spectrum over time. Coronopus didymus, Stellaria media and Lolium spp were present in relatively large numbers throughout the season. Some weeds only occurred late in the season meaning they could be successfully controlled by early sowing. It could be concluded that it is possible to obtain high pea yields by using the right sowing date and appropriate seed rate as a means of low input weed management strategy.