Grass weed competition with bread wheat in Ethiopia. 2: Prediction of grain yield loss and implications for economic weed control

Abstract

Two multi-year studies were conducted in Ethiopia to examine the effects of competition by the predominant grass weed species on bread wheat (Triticum aestivum L.). In the first experiment, the effects of four grass weed species (Avena abyssinica Hoechst, Lolium temulentum L., Snowdenia polystachya Fresen (Pilg), and Phalaris paradoxa L.) at eight seedling densities (from 0 to 320 m^2) on wheat grain yield were studied. A. abyssinica and S. polystachya were highly competitive, resulting in a greater reduction of wheat grain yield (i.e., 85 and 86%, respectively, at 320 seedlings m^-2) than L temulentum and P. paradoxa. L temulentum exerted a greater competitive effect than P. paradoxa. Competitiveness of the grass weeds varied with weed seedling density. The second experiment studied the competitive interactions of Avena fatua L. sown at four seedling densities (from 0 to 90 m^-2) in competition with four bread wheat cultivars commonly grown by peasant farmers in Ethiopia. The semi dwarf cultivar Dashen was the most sensitive to A. fatua competition, exhibiting a yield loss of 63% at the maximum density of 90 wild oat seedlings m^-2. Competitive indices were derived from each experiment to facilitate the prediction of wheat grain yield loss, and to derive economic thresholds for herbicidal intervention in relation to weed seedling density.