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The awareness of agronomic practices that affect the resistance selection of weeds to a particular herbicide is of utmost importance in order to advocate management practices that aim to avoid or prolong the resistance. The objectives of this study were to identify and map the occurrence of the wild poinsettia's low-level resistance to glyphosate in Rio Grande do Sul State (RS), Brazil, and to define the main agronomic factors associated with the selection of these biotypes. Seed and / or soil samples in areas with suspected resistance were collected in Roundup Ready® (RR) soybean crops in different counties in the RS region during the 2010/11 and 2011/12 seasons. A questionnaire on the operations history in the area was applied at each site in order to establish relationships between the distribution of wild poinsettia with cases of suspected resistance to glyphosate and the likely agronomic factors involved in this occurrence. The study included the response of wild poinsettia biotypes with suspected resistance to glyphosate and an analysis of the questionnaires carried out with producers. The main agronomic practices used by producers that favor the emergence of resistant biotypes were the continued cultivation of the RR® soybean; an overdependence on the use of glyphosate; a low rate of crop rotation and efficient chemical alternatives for wild poinsettia control and management. [ABSTRACT FROM AUTHOR]

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