Dose-response curves of Lolium multiflorum biotypes resistant and susceptible to clethodim

Abstract

-Chemical control with herbicides, especially glyphosate, is the main method used to control ryegrass. However, the repeated use of glyphosate has selected resistant ryegrass biotypes. Thus, the ACCase inhibitor herbicides have become the main alternative to control glyphosate-resistant biotypes, being widely used by farmers in Rio Grande do Sul. Repeated use of ACCase inhibitors, in turn, have selected ryegrass biotypes resistant to this herbicide mechanism. Thus, the objective of this study was to evaluate the response of ryegrass biotypes to different clethodim rates by dose-response curves. Increasing doses (0, 12, 24, 48, 72, 96, 144 and 192 g a.i. ha -1 ) of the herbicide clethodim were applied at the 3-4 ryegrass leaf stage. The variables control at 14 and 28 days after treatment (DAT) and shoot dry weight were evaluated. The data were fitted by nonlinear regression log-logistic and C 50 and GR 50 were calculated based on the equation. The resistance factor was obtained by the ratio of C 50 or GR 50 of the resistant biotype by matching the susceptible biotype. Based on the equation parameters, the doses of GR 50 64.7 and 234.5 g a.i. ha clethodim were obtained, at 28 DAT for the susceptible and resistant biotypes, respectively. The ryegrass biotype denominated Cotril is resistant to clethodim, being controlled with a dose 15.3 times greater than that of the susceptible biotype, and a 50% reduction of this biotype occurs with a dose 3.62 times higher than that of the susceptible one.Keywords: ryegrass, cyclohexanodiones, herbicide resistance. (0, 12, 24, 48, 72, 96, 144 e 192 RESUMO -

Eficácia e fitotoxicidade de herbicidas aplicados para o manejo de plantas daninhas em cevada

“…Cabe destacar que mesmo que esse produto tenha controlado 80% da população do azevém que infestou a cevada a recomendação do mesmo para o manejo químico dessa planta daninha torna-se preocupante, já que essa espécie é muito competitiva com a cultura e ainda é resiste aos mecanismos de ação inibidores da EPSPs, ALS e ACCase (Roman et al, 2004;Mariani et al, 2012;Vargas et al, 2013 5,57 1 Médias seguidas de letras minúsculas distintas, na coluna, diferem entre si pelo teste de Tukey (p≤0,05) e por *, na linha, entre os genótipos de cevada para cada variável resposta, diferem entre si pelo teste t (p≤0,05).…”

“…As plantas daninhas competem com as culturas pelos recursos disponíveis no ambiente, liberaram substâncias alelopáticas ou podem hospedar pragas e doenças e, como consequência, ocasionarem perdas de produtividade e de qualidade dos grãos (Vargas et al, 2007;Galon et al, 2010;Galon et al, 2011).…”

Eficácia e fitotoxicidade de herbicidas aplicados para manejo de plantas daninhas infestantes do trigo

“…Cyhalofop-p-buthyl showed an intermediate efficiency on the ryegrass plants and variable between the wheat cultivars, controlling an average of 52,5;82,8;88,4;89,0;85,8;92,0;81,5 and 78,8%,respectively,at 07,14,21,28,35,42 DAT, (Tables 3 and 4). It is worth considering that cyhalofop-p-buthyl, even in control of more than 80% of the ryegrass population that infested the wheat, must be handled cautiously for this weed, because this species is very competitive with the crop and is also resistant to herbicides belonging to the action mechanisms that inhibit EPSPs, ALS and ACCase (Roman et al, 2004;Vargas et al, 2013). Bastiani et al (2012), when evaluating the alternatives for the handling of ryegrass biotypes resistant and susceptible to glyphosate, saw that cyhalofop-pbuthyl presented 100% of control for the susceptible biotype and 89% for the resistant biotype.…”

EFEITO DA ADUBAÇÃO NITROGENADA E INOCULAÇÃO DE SEMENTES COM Azospirillum brasilense SOBRE CARACTERÍSTICAS COMERCIAIS DE MINIMILHO NO PERÍODO DE OUTONOINVERNO NO NOROESTE DO PARANÁ

“…No Brasil, o azevém resistente ao herbicida glyphosate foi inicialmente identificado em culturas anuais e pomares de maçã no estado do Rio Grande do Sul (Roman et al, 2004). Vargas et al (2013) NUNES et al, 2010;NASCIMENTO et al, 2012;ALMEIDA et al, 2014)…”