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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730
EISSN: 1021-9730
Vol. 5, No. 4, 1997
Bioline Code: cs97043
Full paper language: English
Document type: Research Article
Document available free of charge

African Crop Science Journal, Vol. 5, No. 4, 1997

 en Grass weed competition and calculated economic threshold densities in bread wheat in Ethiopia
Tessema, Taye & Tanner, D.G.


Competition effects of four of the predominant grass weed species in Ethiopia (Avena abyssinica Hoechst, Lolium temulentum L., Snowdenia polystachya Fresen (Pilg), and Phalaris paradoxa L.) on the grain yield, yield components and morphological characters of bread wheat (Triticum aestivum L.) were studied in Western Shewa Zone of Ethiopia. The four grass species varied significantly in their effects on wheat tillering, leaf area index (LAI), number of fertile spikes m-2, grains per spike, spike length, thousand grain weight, straw, biomass and grain yield, harvest index and plant height. Avena abyssinica and S. polystachya were the most competitive, 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 weed density of 320 seedlings m-2 ranged from 48 to 86% across the four grass species studied. The wheat yield components most affected by weed competition were number of fertile spikes m-2 and number of seeds spike-1. Weed morphological characters (i.e., number of tillers, LAI, number of panicles, and plant height) varied markedly among species and in direct proportion with weed seedling density. Plant height and LAI appeared to be the factors most closely associated with weed competitive ability with bread wheat. 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.

Competition, grass weeds, herbicides, wheat, yield components, yield loss

Tessema, Taye & Tanner, D.G.


Les effets de competition de quatre des especes de mauvaises herbes predominantes en Ethiopie (Avena abyssinica Hoechst, Lolium temulentum L., Snowdenia polystachya Fresen (Pilg), et Phalaris paradoxa L.) sur le rendement en grain, les composantes du rendement et les caracteres morphologiques du ble tendre (Triticum aestivum L.) ont ete etudies dans la zone Shewa Ouest d'Ethiopie. Les quatre especes de mauvaises herbes varient significativement dans leurs effets sur le tallage du ble, l'index de la surface foliaire (LAI), le nombre d'epis fertiles au m2 et de grains par epis, la longueur de l'epi, le poids de 1000 grains, la paille, la biomasse, le rendement en grains, l'index de recolte et la taille de la plante. A. abyssinica et S. polystachya etaient les plus competitives, reduisant les composantes du rendement du ble et les caracteres morphologiques dans une plus large mesure que L. temulentum et P. paradoxa. Les effets de l'interaction, espece de mauvaise herbe par densite de semis, etaient significatifs pour la plupart des cultures et des caracteres de la mauvaise herbe mesures, indiquant une reponse differentielle pour les especes individuelles. La reduction du rendement en grain du ble a la densite maximale de mauvaise herbe de 320 plantules au m-2 variaient de 48 a 86% chez les quatre especes de graminees etudiees. Les composantes du rendement du ble les plus affectees par la competition des mauvaises herbes etaient le nombre d'epis fertiles au m-2 et le nombre de graines par epis. Les caracteres morphologiques des mauvaises herbes (i.e., nombre de talles, LAI, nombre de panicules et taille de la plante) variaient nettement entre les especes et en proportion directe avec la densite de plantules de mauvaises herbes. La taille de la plante et LAI semblaient etre les facteurs les plus etroitement associes a l'habilite de competition de la mauvaise herbe avec le ble. Les pertes de rendement en competition ont ete ajustees a un modele rectangulaire hyperbolique pour faciliter les previsions des pertes de rendement en grains de ble et pour determiner les seuils economiques d'application d'herbicides en relation avec la densite de plantules de mauvaises herbes.

Mots Clés
Adventices, ble, competition, composantes du rendement, herbicide, perte du rendement

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