Influence of emergence time and density on redroot pigweed (Amaranthus retroflexus)

Field studies were conducted at two locations near Manhattan, KS, in 1994 a nd 1995 to determine the influence of density (0.5, 1, 2, 4, and 12 plants m(-1) row) and time of emergence on redroot pigweed growth in monoculture o r with sorghum. Redroot pigweed was seeded at sorghum planting and at the t hree- to four-leaf stage of sorghum in plots with sorghum or alone. When re droot pigweed grew with sorghum, dry matter and seed production were reduce d with later times of emergence. In monoculture, there was no reduction in dry matter or seed number between the emergence dates studied. Redroot pigw eed dry matter and seed production per plant were reduced as plans density increased for plants grown in monoculture. The same trend was observed for redroot pigweed grown with sorghum chat did not emerge early relative to so rghum. Plants grown at low density exhibited more lateral growth than when grown at higher densities because of intraspecific competition.