Seletividade de herbicidas e dinâmica populacional de plantas daninhas na cultura do girassol para a produção de biodiesel

Abstract

Experiments were conducted in Prudente de Morais County, Minas Gerais State, in 2010 and 2011 years, with the objective of to evaluate selectivity and efficiency of pre and post-emergence herbicides in sunflower crop, as well as to study weeds populacional dynamic. The work conducted in 2010 was carried out in greenhouse, in a randomized complete block design, with 11 treatments and three replications. Treatments consisted by ten herbicides, four in pre emergence and six in post-emergent of the crop (alachlor, imazaquin, metribuzin, trifluralin, chlorimuron-ethyl, fenoxaprop-p-ethyl, [fluazifop-p + fomesafen], imazapyr, imazethapyr e sethoxydim) and a check. The following characteristics were evaluated: phytotoxicity effects, plants height, leaves number and dry biomass of shoot and root 60 days after product applications. In 2011, the work was accomplished in filed conditions following a randomized complete block design with six treatments and four replications. The treatments consisted of two pre-emergent herbicides: alachlor and trifluralin, two post-emergence: fenoxaprop-p-ethyl and sethoxydim and two checks (with and without weeding). Crop cycle, flowering initial, plant height, stem diameter, achenes physiologically mature, chapters diameter, broken plants number, lodged plants number, final stand and achenes yield were evaluated. Based on the obtained results, it was possible to conclude that herbicides that showed higher toxicity to sunflower plants were: imazaquin, metribuzin, chlorimuron-ethyl, [fomesafen + fluazifop-p], imazapyr and imazethapyr. The pre emergent herbicides alachlor, trifluralin, fenoxaprop-p-ethyl and sethoxydim were selective to sunflower crop. Fenoxaprop-p-ethyl herbicide may be used in a program of weeds integrated management in sunflower crop, because only trifluralin, alachlor and sethoxydim herbicides are registered for this crop in Brazil.