This study was carried out in Cumbacillo, Morales on a sandy loam soil with a crop of copwpea (Vigna unguiculata L. Walp). The crop was weeded in part and in part the weeds were allowed to grow. The objetive was to determine the critical period of competition between the weeds and cowpea crop. The experiment used 6 treatments with weeds permitted to grow and 6 treatments weeded what comprehend periods from until 10, 20, 30, 40, 50 y 60 days respectively. Two control plots were maintained during the experiment, one with weeds permitted to grow and one without weeds. Each plot had an area of 16.1 m2. The critical moment of weed competition in the case of white cowpea Cumbaza INIA was seen within the f1rat 50 days (treatment with weeds). During this period the moat severe reductions in yiel of cowpea were observed. The white cowpea Cumbaza INIA was planted September 25, 1995 and harvested N...