ABSTRACT
ABSTRACT: Cyhalofop-butyl stands out among the herbicides in the control of imidazolinone-resistant Echinochloa species; but, rice farmers are not always satisfied with the control achieved with this herbicide. The objectives were to evaluate in regional scale the susceptibility of Echinochloa populations to cyhalofop-butyl, and quantify the effect of the weed phenology on its efficacy of control. For this, three trials were carried out under greenhouse conditions with a fully random design, using Echinochloa populations collected in rice fields in the southern region of Brazil. In two trials, the susceptibility level of 156 (2012/13 growth season) and 103 (2013/14 growth season) populations were evaluated with the application of cyhalofop-butyl at 360g ha-1. In other trial, in which treatments were arranged in a bi-factorial design (A = 6 x B = 5), it was evaluated six cyhalofop-butyl rates and five phenological stages of E. crus-galli populations. Echinochloa populations had showed differential susceptibility to cyhalofop-butyl, especially in the 2013/14 growth season, where 20 out of the 103 populations had control lower than 90%. The efficacy of this herbicide was inversely proportional to the phenological stage, and the application timing delay contributed directly to the decrease of susceptibility to the herbicide. Cyhalofop-butyl is an effective alternative to control imidazolinone-resistant Echinochloa populations, as long as the application timing occurs in the early phenological stages (2 to 4 leaves).
RESUMO: Cyhalofop-butyl destaca-se dentre os herbicidas usados no manejo de populações de capim-arroz resistente às imidazolinonas, mas nem sempre o orizicultor fica satisfeito com o resultado obtido com este herbicida. Objetivou-se avaliar a suscetibilidade de populações de capim-arroz (Echinochloa spp.) ao cyhalofop-butyl e, quantificar o efeito da fenologia da infestante sobre a eficácia do seu controle. Para isto, três experimentos foram realizados em casa de vegetação com delineamento inteiramente casualizado, utilizando-se populações de capim-arroz coletadas na região Sul do Brasil. Em dois experimentos, a suscetibilidade de 156 (safra 2012/13) e 103 (safra 2013/14) populações foram avaliadas frente à aplicação do herbicida cyhalofop-butyl na dose de 360g ha-1. Em outro experimento, em que se arranjaram os tratamentos em esquema bi-fatorial, foram avaliados seis doses do herbicida e cinco estádios fenológicos de populações de E. crus-galli. Foi verificada variação na resposta das populações de capim-arroz ao cyhalofop-butyl, em especial na safra 2013/14, em que 20, das 103 populações testadas, tiveram controle menor que 90%. A eficácia do controle foi inversamente proporcional ao estádio fenológico e, o atraso no controle da infestante contribui diretamente para a diminuição da sua suscetibilidade ao herbicida. Cyhalofop-butyl é uma alternativa eficaz para controlar capim-arroz resistente às imidazolinonas, desde que a aplicação ocorra nos estádios iniciais de desenvolvimento (2 a 4 folhas).
ABSTRACT
Echinochloa colona (L.) Link is a very problematic weed in up land and medium land rice causing significant reduction in yield. In the present investigation, laboratory and field experiments were conducted to evaluate the nature of interaction E. colona on germination and growth of the up land rice cultivar ‘Vandana’. The effects of decomposing and decomposed aqueous leachates (1-10%w/v) obtained from the dried biomass of 20, 30, 40 and 60 days old E.colona plants were studied on rice using petridish bioassay technique with three different types of culture media like filter paper, soil, and soil + activated charcoal. The decomposing leachates of E. colona showed strong toxic effect on root and shoot growth of rice, the highest being noted with 10% leachates of 60 days old plant residue. It inhibited root and shoot growth by 100% and 43.9% respectively as compared to control. The corresponding decomposed leachates inhibited rice germination by 90% and root and shoot growth by 70 and 25% respectively. These toxic effects of leachates showed in filter paper medium were significantly reduced in soil and soil plus activated charcoal media proving their allelopathic nature. In a field experiment, E. colona and rice were grown in proportions of 1:1, 1: 2 and 1:4, the total plant density being maintained at 100 pants m-2. The height and dry matter of rice were adversely affected with increasing in E. colona population. From another similar field trial, data on dry matter of 20, 30, 40, and 60 days old plants were taken and their plant relative yield (PRY) and relative yield total (RYT) values were calculated. The PRY and RYT values were found to be less than unit (<1) throughout the growth period studied which suggested the presence of severe antagonistic interspecific interaction between rice and E.colona due to allelopathy.