Resumo -As principais plantas daninhas encontradas na cultura do trigo são o nabo e o azevém, e seu controle em pós-emergência é baseado em herbicidas inibidores da enzima acetolactato sintase (ALS) e acetil coenzima A carboxilase (ACCase) que, em função da resistência, limita as opções de controle. Associações de herbicidas têm sido utilizadas em pós-emergência do trigo, porém, seus efeitos na cultura são pouco conhecidos. O objetivo deste trabalho foi avaliar a seletividade de associações de herbicidas e doses aplicados em pós-emergência do trigo. Foram realizados três experimentos a campo em sistema de semeadura direta, no delineamento de blocos ao acaso com três repetições. Os experimentos foram conduzidos nos municípios de Santa Bárbara do Sul-RS, Cruz Alta-RS e Tupanciretã-RS. Foram estudadas doses e associações entre os herbicidas 2,4-D, metsulfuron-methyl, iodosulfuron, piroxsulam e saflufenacil aplicados no perfilhamento do trigo. As variáveis avaliadas foram fitotoxicidade aos sete, 14, 21 e 35 dias após a aplicação (DAA), rendimento de grãos (kg ha -1 ) e peso hectolitro dos grãos de trigo (PH), sendo os dados dos três experimentos analisados de forma conjunta. Aos 35 DAA as maiores fitotoxicidades foram observadas para metsulfuron-methyl na dose de 9 g i.a. ha -1 e para saflufenacil associado ao metsulfuron-methyl. Os resultados de rendimento de grãos demonstraram que a associação entre 2,4-D e metsulfuron-methyl, saflufenacil isolado ou associado à metsulfuron-methyl e o iodosulfuron-methyl foram seletivos para o trigo. O aumento da dose de metsulfuron-methyl (6 e 9 g i.a. ha -1 ) e a dose de registro de piroxsulam causaram redução significativa na rendimento de grãos de grãos de trigo na média dos três experimentos. O PH dos grãos de trigo não foi influenciado pelos herbicidas estudados. Palavras-chave: Triticum aestivum, mistura de herbicidas, mistura em tanque, resistência Abstract -The main weeds in wheat are wild radish and ryegrass, and its post-emergence control is based on herbicides inhibiting the enzyme acetolactate synthase (ALS) and acetyl coenzyme A carboxase (ACCase), which as a function of resistance limits the control options. Herbicide combinations have been used for post-emergence of wheat; however, the effects of herbicidal combinations are poorly understood. The objective of this work was to evaluate the selectivity of Piasecki et al. Rev. Bras. Herb., v.16, n.4, p.286-295, out./dez. 2017 287
-The commercial release of the Roundup Ready ® soybean helped the management of weeds and allowed the application of glyphosate during the post-emergence of the culture. However, the intensive use of this herbicide selected resistant hairy fleabane biotypes and hindered control. Many works evaluate the technical effectiveness of herbicides, however, most of the times; the economic return is not analyzed when making decisions about the choice of which herbicide to apply. The aim of this work was to evaluate the technical effectiveness and the economic return of applying herbicide associations and rates in the management of glyphosate-resistant hairy fleabane, in soybean pre-emergence. The experiment was carried out in randomized block design with four replicates. Treatments consisted in associations among glyphosate, 2.4-D, saflufenacil, diclosulam, chlorimuron-ethyl and flumioxazin. The analyzed variables were hairy fleabane control and phytotoxicity on soybean on 7, 14, 21 and 35 days after the application and yield of soybean. The economic return of treatments was calculated according to the cost of the herbicides and the soybean yield. Results about control and yield shows that the association of glyphosate, chlorimuron-ethyl, flumioxazin and 2.4-D and of glyphosate, chlorimuron-ethyl, 2.4-D and saflufenacil presented the best technical effectiveness response and the use of glyphosate, chlorimuron-ethyl and 2.4-D presented the best economic return. However, the increase in chlorimuron-ethyl rates and its association with flumioxazin did not improve the control of hairy fleabane. Keywords: Conyza spp.; control; cost; herbicide association Resumo -
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