Field pea cultivar and weed response to crop seed rate in western Canada

Weed competition is a serious limitation to field pea (Pisum sativum L.) production. Trials were conducted in northeastern Saskatchewan to determine the effects of field pea growth habit, stand density and herbicide treatments on weed growth and on field pea stand and yield. Century, a long-stem leafy type, Tipu, a long-stem semi-leafless type, and Express, a short-stem leafy type, were seeded at 6, 12, 25, 50 and 100 seeds m−2. Some of each cultivar was unsprayed sprayed with a sethoxydim-metribuzin tank-mix for control of grass and broadleaf weeds. Field pea growth habit (cultivar) did not affect number of weeds, but increasing stand density (seed rate) reduced weed numbers in all 3 yr. Express reduced above-ground dry matter production of broadleaf weeds in 1988 and 1991. Increasing seed rate reduced above-ground dry matter production of weeds in all 3 yr. Field pea yield increased with increasing seed rate to a rate between 50 and 100 seeds m−2. Herbicide application reduced weed dry matter production, with the largest effect at low field pea populations. Despite differences in growth habit, the three cultivars competed similarly with weeds. High populations of field peas competed well with weeds and may not require herbicide application, but if producers retain thin stands, good weed control will be critical to attaining high crop yield. Key words: Field pea, Pisum sativum L., seed rate, weed competition, growth habit