Competition of Weeds Dominated by Wild Oat (Avena sterilis   L.) in Wheat (Triticum durum Desf.) in Jordan

Wheat is the main field crop grown in Jordan. Productivity is low due to different factors, including erratic rainfall, poor soil fertility and weed competition. A field experiment was carried out at the University of Jordan Research Station for two growing seasons to determine the effect of weed competition on growth and yield of wheat (Triticum durum Cv. “Hourani”). Treatments consisted of either allowing weeds to infest the crop or maintaining the crop weed-free for increasing durations after emergence. Results showed that, the longer the periods of weed competition, the greater the loss in crop growth and yield. Average reductions in grain and straw yields were 41% and 37%, respectively. The highest grain yield obtained was from weed-free, and the lowest was in weed-infested plots for the entire growing season. Average grain yield was not significantly different at 14 to 49 days of weed-infested periods, while none of the weed-free periods produced a yield similar to that of the weed-free control. However, maintaining a weed-free crop for three weeks after emergence significantly increased grain yield compared with the weed-infested control. High rainfall in the first season almost doubled weed growth and greatly reduced wheat growth and yield compared with the second season. To determine the critical period of weed competition and the influence of weed infestation on wheat grain yield, Gompertz and logistic equations were fitted to data representing increasing duration of weed-free and weed-infested periods, respectively. Based upon an arbitrary 5% level of average grain yield loss in the two years, the critical period of weed competition occurred at 0–49 days after wheat emergence, which corresponded with the rapid increase in weed biomass.