Weeds in new seedings of alfalfa (Medicago sativa) for seed production: competition and control.
Lucerne cv. Vernal sown in April in rows 55 cm apart and kept free of weeds produced 820 kg/ha of seed during the year of sowing. Competition from a dense population (40 plants/m of row) of mixed species of annual weeds reduced the seed yield to 45 kg/ha. Competition from a dense population (55 plants/m of row) of broad-leaved weeds, a light population (4 plants of row) of broad-leaved weeds or a heavy population (75 culms/m of row) of Echinochloa crus-galli reduced yields to 80, 310 and 160 kg/ha, respectively. A weed management system consisting of EPTC at 2.2 kg/ha or profluralin at 1.1 kg/ha applied before or at sowing, 2,4-DB at 1.1 kg/ha applied post-em., trifluralin at 0.8 kg/ha incorporated when the lucerne was 20 cm high, inter-row cultivation and between 7 and 17 h/ha of hand labour was required to keep the crop free of weeds until harvest. Without herbicides, the hand labour requirement was 930 h/ha. Lucerne seed yield with herbicides was similar to that with hand-weeding only.