Wild oat is the most serious grass weed in Argentine barley crops and its control has concentrated on herbicide strategies. Increasing crop density could be an effective strategy to reduce the effect of wild oat on barley yield. However, limited research has been conducted to evaluate the effect of crop density on the competitive balance between barley and spontaneous populations of wild oat. A field experiment was conducted in 1992, 1993, and 1999, to study the effect of spontaneous populations of wild oat on barley sown at densities of 160, 220, and 280 plants/m². Wild oat density averaged 84 plants/m². Wild oat biomass increased linearly with weed density in all treatments but was reduced by increasing barley seeding rates. Barley biomass and yield were not affected by wild oat at high crop sowing densities, but for the low and medium barley densities, yield loss was almost 25% when 70 wild oat plants/m² were established. Barley yield loss was mostly related to competition from the early emerged wild oat. The relationship between yield losses and wild oat density was equally significant when the whole population or only early emerged individuals of the weed were considered.

Nomenclature: Wild oat, Avena fatua L. #³ AVEFA; barley, Hordeum vulgare L.

Additional index words: Wild oat interference in barley, integrated wild oat management, seeding rates of barley.