Determination of economic threshold densities for the mayor weed species competing with bread wheat in Ethiopia
1999
Taye Tessema | Tanner, D.G.
Competition effects of four grass weed species (Avena abyssinica, Lolium temulentum, Snowdenia polystachya, and Phalaris paradoxa) and three broadleaf weed species (Guizotia scabra, Amaranthus retroflexus, and Galium spurium) on he grain yield, yield components and morphological characters of bread wheat (Triticum aestivum) were studied in Ethiopia. The weed species varied significantly in their effects on the number of fertile wheat spikes m-2, grains per spike, thousand grain weight, biomass and grain yield, harvest index and plant height. A. abyssinica and S. polystachya were the most competitive grass weeds, reducing wheat yield components and morphological characters to a greater extent than L. temulentum and P. paradoxa. Grass species by seedling density interaction effects were significant for most of the crop and weed characters measured, indicating a differential rate response for individual species. The reduction in wheat grain yield at the maximum grass weed density of 320 seedlings m-2 ranged from 48 to 86percent across the four species studied. Among the three broadleaf weed species, G. scabra exerted the greatest effect on wheat grain yield. The wheat yield reduction at the maximum broadleaf weed seedling density of 160 seedlings m-2 was 47.8,29.6 and 18.6percent for G. scabra, A. retroflexus, and G. spurium, respectively. Competitive yield losses were fitted to a rectangular hyperbola model to facilitate the prediction of wheat grain yield loss, and to derive economic thresholds for herbicidal intervention in relation to weed seedling density
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