Summary. Experiments arc reported that demonstrate that there is mutual interference between kale and Chenopodium album when grown in association. As the plants grow, those at high density, whether in mixtures or in pure stands, interfere with each other and individual plant weight and leaf area are reduced. By changing the time:of Introduction of one of the species into a mixture it was shown that kale suffered heavy mortality when C. album had an initial advantage. When kale was introduced before C. album the weed remained stunted but there was no mortality. The weed exerted an early effect of kale. The ability of C. album to interfere with kale, seems to be related to its plasticity. It is able to grow rapidly, to trap light effectively and even under adverse conditions to set seed. Etude sur le pouvoir de compétition de Chenopodium album L. I. Recherches sur la compétition enire les choux et C. album