Demography of Wild Oat in Barley Crops: Effect of Crop, Sowing Rate, and Herbicide Treatment

Wild oat (Avena fatua L.) is a major weed in barley (Hordeum vulgare L.) in Argentina. During 1993, 1994, 1995, and 1996, demographic studies of wild oat in barley crops were conducted to assess the effect of herbicide treatment, crop, and sowing rate on the demographic processes of seedling establishment, survival rate, reproductive performance, preharvest seed dispersal rate, and fate of seed in the soil during the fallow period. The herbicide was diclofop‐methyl: methyl 2‐[4‐(2,4‐dichlorophenoxy)phenoxy]propanoic acid. Increasing barley sowing rate from 160 plants m−2 to 280 plants m−2 effectively reduced the amount of wild oat seeds that entered the soil seed bank by 50% through lowering fecundity. Diclofop‐methyl reduced the number of seeds that entered the soil seed bank sevenfold (1050 vs. 140 seeds m−2) through a reduction in both seedling survivor rate and reproductive output. In addition, the diclofop‐methyl treatment delayed the onset of seed maturity and reduced the dormancy level of the seeds produced by the surviving plants. Half the number of wild oat seeds entered the seed bank in a barley than in a wheat (Triticum aestivum L.) crop. This was through a lower wild oat reproductive output and a higher rate of seed dispersal related to the later harvest time of wheat relative to barley. These data indicate that integrated control of wild oat should include herbicide treatment, crop selection, and sowing rate.