Container experiments were conducted in the Dominican Republic to determine the influence of gibberellic acid treatment on the competitive ability of tomato, eggplant and bell pepper against the weed Parthenium spp. until crop flowering. The effect of gibberellic acid rates on competitiveness was determined by the changes in relative crowding coefficient values (RCC) in a replacement series of each crop and the weed. Results indicate that gibberellic acid increased crop biomass and thus RCC as rates increased. Bell pepper was the most responsive crop. Since the critical interference period usually occurs before flowering, gibberellic acid treatment at the time of transplanting might prove to be an effective means to improve the competitive ability of this crop against Parthenium spp.