Influence of barnyardgrass (Echinochloa crus-galli) time of emergence and density on corn (Zea mays).
Field experiments were conducted at Elora and Woodstock in Ontario in 1994 and 1995 to determine the influence of emergence time and barnyardgrass density on corn [maize] cv. Pioneer 3902 yield loss, leaf area at 50% silking, and barnyardgrass seed production. Selected barnyardgrass densities up to 200 plants m-1 were established within 12.5 cm on either side of the corn row. Barnyardgrass seeds were planted concurrently with corn and at the 3- to 5- or 1- to 2-leaf stage of corn growth in 1994 and 1995, respectively. Barnyardgrass density and seedling emergence relative to corn influenced the magnitude of corn yield loss. Maximum corn grain yield loss ranged from 26 to 35% for early emerging barnyardgrass, and less than 6% yield loss occurred from barnyardgrass seedlings emerging later than the 4-leaf stage of corn growth. Changes in corn leaf area index at 50% silking reflected the level of barnyardgrass competition in corn. Maximum leaf area reduction ranged from 21 to 23%. Barnyardgrass seed production varied with time of seedling emergence and density. Ten barnyardgrass plants emerging up to the 3-leaf stage of corn growth produced 14 400 to 34 600 seeds m-2 compared to only 1200 to 2800 seeds m-2 from plants emerging after the 4-leaf corn stage.