An investigation to study the effect of weed competition on American cotton was carried out at Cotton Research Station, Abohar during kharif 1991 and 1992. The weeds associated with the crop were: Trianthema portulacastrum L., Eleusineindica L., Cyperus rotundus L, Celosia argentea L., Digera arvensis L., Tribulus terrestris L., Xanthium strumarium L., Cenchrus catharticus Land Amaranthus viridis L. Weed population increased between 30–60 days after sowing and decreased thereafter. Weed competition during the first 30 days after sowing resulted in an average yield loss of 10.5 per cent which increased to 57.1 per cent with full season competition. The seed cotton yield increased from 1890k.g/ha to 3021 k.g/ha as the initial weed-free period was increasedfrom 30 days after sowing (DAS) to full season. The critical period of weed competition in American cotton prevailed upto 60 DAS druing which the crop should be kept free of weeds to prevent the potential losses in seed cotton yield.
