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Previous issue date: 2011 === Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (Capes) === Funda??o de Amparo ? Pesquisa do estado de Minas Gerais (FAPEMIG) === Objetivou-se com este trabalho avaliar a seletividade de herbicidas aplicados em p?s emerg?ncia sobre a cultura da mandioca (Manihot esculenta Crantz). Para isso, foram realizados tr?s experimentos em ambiente protegido. No primeiro, avaliou-se os efeitos de 22 princ?pios ativos aplicados aos 60 dias ap?s a brota??o das manivas sobre o crescimento inicial das plantas. Os sintomas de intoxica??o foram mais percept?veis aos 21 dias ap?s o plantio para a maioria dos herbicidas testados. Ametryn, ametryn + trifloxysulfuron-sodium, atrazine, diuron + hexazinone e sulfentrazone provocaram as maiores redu??es de mat?ria seca e causaram os maiores danos vis?veis, ao contr?rio, bentazon, fluazifop-p-butil, mesotrione e tembotrione foram os menos t?xicos ? cultura. O segundo experimento teve como objetivo avaliar a toler?ncia de cultivares de mandioca a aplica??o em p?s-emerg?ncia dos herbicidas fluazifop-p-butil e fomesafen em mistura e de forma isolada. Na primeira avalia??o de intoxica??o visual, aos 7 dias ap?s a aplica??o, sintomas mais vis?veis de intoxica??o ocorreram nas plantas de mandioca tratadas com a mistura de herbicidas e tamb?m com fomesafen de forma isolada. A mistura mostrou-se t?xica provocando redu??es na mat?ria seca foliar, mat?ria seca caulinar, mat?ria seca da parte a?rea, di?metro do caule, ?rea foliar e altura da planta das cultivares. Apesar dos elevados ?ndices de intoxica??o pelo herbicida fomesafen, n?o foi observado varia??es significativas no ac?mulo de mat?ria seca pelas cultivares. Tratamentos ? base de fluazifop-p-butil foram pouco t?xicos ? cultura promovendo resultados semelhantes aos observados para testemunha. No terceiro experimento avaliou-se a toler?ncia da mandioca ao herbicida mesotrione aplicado aos 30 dias p?s-brota??o da cultura. Os maiores valores de intoxica??o foram encontrados aos 14 e 28 DAA. O herbicida n?o afetou as vari?veis altura de planta, di?metro do caule, n?mero de folhas, ?rea foliar e ac?mulo de mat?ria seca de folha, caule, ra?zes e total. De modo geral os herbicidas bentazon, fluazifop-p-butil, mesotrione e tembotrione apresentaram elevada seletividade a mandioca. No entanto n?o se recomenda a aplica??o em p?s-emerg?ncia da mistura fluazifop-p-butil e fomesafen por provocarem elevada intoxica??o as plantas. O herbicida mesotrione causou baixa intoxica??o aos cultivares de mandioca apresentando elevado potencial para o uso nos programas de manejo de plantas daninhas na mandioca. === Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Produ??o Vegetal, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2011. === ABSTRACT The objective of this work was to evaluate the selectiveness of herbicides applied after the sprouting of cassava plants (Manihot esculenta Crantz). To this end three experiments were carried out under a greenhouse. The first experiment evaluated the effects of 22 herbicides, applied 60 days after the emergence of cassava, on the initial growth of the plants. The most visible symptoms of poisoning occurred at 21 days after planting for most products tested. Ametryn, ametryn + trifloxysulfuron-sodium, atrazine, diuron + hexazinone and sulfentrazone caused the greatest reductions in dry matter and caused major damage visible; however, bentazon, fluazifop-p-butyl, mesotrione and tembotrione were the least toxic to the culture. The second experiment aimed to evaluate the tolerance of cultivars of cassava to the post-emergence application of fluazifop-p-butyl and fomesafen in combination and isolately. In the first visual assessment of intoxication, at 7 days after application, the most visible symptoms of intoxication have been observed in the plants treated with the mixture diuron + hexazinone and fomesafen isolated. The mixture proved to be very toxic causing reductions in leaf dry matter, stem dry matters, aerial dry matter, in the stem diameter, the leaf area and the plant height. Despite high rates of poisoning by the herbicide fomesafen was not observed significant variations in dry matter accumulation by cultivars. Treatments based on fluazifop-p-butyl were less toxic to the culture, being these results similar to those observed for the control sample. In the third experiment there was evaluated the tolerance of cassava to the herbicide mesotrione applied at 30 days after the emergency culture. The highest values of poisoning were found at 14 and 28 DAA. The herbicides did not affect the variables plant height, stem diameter, leaf number, leaf area and dry matter accumulation of leaf, stem, roots and total dry matter. In general, the bentazon, the fluazifop.p.butil, and the tembotrione showed high selectivity to the culture. However, the mixture fluazifop-p-butyl + fomesafen is not recommended in post-emergence application because caused toxicity to plants. The herbicide mesotrione caused low toxicity to cassava cultivars showing high potential for use in weeds management programs for cassava.
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