A study was conducted at the IAV Hassan II experimental station in the Gharb region, Morocco. The objectives were to compare the competitive capacity of 23 durum wheat (Triticum durum Desf.) varieties and lines under weedy conditions with and without irrigation. Results revealed an important variability between genotypes for all studied parameters. Grain yield losses caused by weeds varied from 10.3 to 48.5% under irrigation, and from 12.3 to 57.2% in the absence of irrigation. Yield analysis showed that, under weedy and irrigated conditions, the most competitive varieties were BD2777, BD2909, BD272, BD1658, Karim, Isly, Tassaout, Sebou, Wassu-4, and Wassu-3. These varieties reduced weed biomass by their relative higher stature. Only Sebou, BD2777, BD2909, BD1658, Tassaout, conserved their competitive advantage in the absence of irrigation. The least competitive varieties were Massa, Jori, Tensift, Belbachir, Sarif, and Cocorit. These varieties are precocious, and presented a plant height less than 70 cm. They also had lower number of green leaves and tillers per plant. The other varieties showed a weak tolerance to weeds: Marzak, Wassu-2, Wassu-1, Jawhar, Yasmine, Oum Rbia, and ACSAD 65.