The highest values of all yield attributes were recorded under the plots kept weed-free upto harvest and minimum in the plots which remained weedy upto harvest. Weed dry weight and weed competition index increased with the increase in the duration of weedy period and decreased with the increase in duration ofweed-free condition. Weed-free conditions beyon91 45 days after transplanting could not bring significant improvement in fruit yield of tomato which indicated that the critical period of crop-weed competition was found to be first 45 days after transplanting.