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Weeds of major economic importance in rice and yield losses due to weed competition  [1981]

Smith, R.J.Jr. International Rice Research Inst., College, Laguna (Philippines); International Weed Science Society, Corvallis, Oregon (USA) [Corporate Author]

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Worldwide, about 350 weed species in more than 150 genera and 60 plant families have been reported as weeds of rice. Species of Gramineae are the most common with more than 80 reported as weeds of rice. Other plant families with numerous species that are common rice weeds include Cyperaceae, Alismataceae, Compositae, Leguminosae, Lythraceae and Scrophulariaceae. The 10 most common weed species of rice worldwide are Echinochloa crusgalis, E. colonum, Cyperus difformis, C. rotundus, C. iria, Eleusine indica, Fimbristylis miliacea, Ischaemum rugosum, Monochoria vaginalis and Sphenoclea zeylanica. Some of these weeds are problems in all rice cultures, and others are problems in only one culture. Ecological and crop production principles that influence the presence and abundance of species or groups of weeds in rice are seeding method, soil moisture, crop rotation, air and soil temperature, land preparation, fertilization, rice cultivar, weed control technology and interactions of these. World losses due to weeds in rice are estimated at 15.=. of world rice production or 56 million metric tons, valued at $12 billion. The most significant losses from weeds are reduced yields and quality of the rice crop. Losses caused by weeds are reduced yields and quality of the rice crop. Losses caused by weeds are influenced by competitive efficiency of weeds and rice, species or group of weed, weed density, duration of weed-crop competition, planting method, cultivar, ferti
lity level, water management, row spacing of the crop, allelopathy and interactions of these.