Critical period of competition between weeds and cowpea

Abstract

The following treatments were included in two experiments carried out at Viçosa, state of Minas Gerais, Brazil: cowpeas in competition with weeds during 12, 24, 36, 48, and 60 days after crop emergence, followed by weed elimination; the same periods in the inverse sequence, i.e., no competition followed by free development of the weeds; plus one treatment always free of weeds, and one always in competition. In the last treatment weed density was about 800 plants per m², including 17 species (in the first experiment) and 16 species (in the second) of both narrow and broad-leaved weeds. The maximum cowpea yield was obtained when the crop was kept free of weeds for a 36-day period after emergence. When weeds were not controlled, yield decreased as much as 70-90%. Competition decreased the cowpea harvest index and increased its plant height and lodging.