Résumé
In Camargue area (France), weed infestation by Bolboschoenus maritimus and Echinochloa crus-gallis is one major irrigated rice production constraint as well for conventional and organic rice cultivation. This two weed species had different competition strategy and impact on rice production depending of their specific morphology and space colonisation modality. For the two weed species the experiment conducted allow to define similar threshold harmfulness for rice. With a Echinochloa crus-gallis or Bolboschoenus maritimus population upper to 8 plants per meter square, the weed competition effect was significant on rice grain yield. (Résumé d'auteur)