Interferência e controle químico de populações de Brachiaria brizantha em cana-de-açúcar

• Autor(a) principal: Tironi, Siumar Pedro
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1148
• topic: Nível de dano econômico; RB867515; Hexazinone; Ametryn; Trifloxysulfurom-sodium; Diuron; MSMA; Economic threshold level; RB867515; Hexazinone; Ametryn; Trifloxysulfurom-sodium; Diuron; MSMA; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOTECNIA

Aiming to reduce production costs of sugarcane and the environmental impact caused by incorrect use of herbicides in this crop, this study took place, composed of four experiments. In the first experiment, sugarcane cultivars were evaluated in coexistence with different populations of Brachiaria brizantha. The objective was to establish the economic threshold level, which is the population density of B. brizantha that economically justified controlling this species. In the second trial, the same treatments were used as the first, assessing the competition for nutrients between sugarcane cultivars and the populations of B. brizantha. In the third, the efficiency of chemical control of B. brizantha at different vegetative stages of this weed was assessed. The fourth experiment evaluated the effects of herbicides used with greater frequency on the crop on technological quality and crop yield. Stalk productivity losses due to the B. brizantha interference were estimated efficiently by the hyperbolic model. The cultivar RB867515 showed higher and the SP801816 lower competitive ability with B. brizantha. Phosphorus was the most limiting nutrient in the environment, with changes in foliar levels in all cultivars when in competition with the highest populations of B. brizantha. The economic threshold level for B. brizantha control was reached with a population of 0.33, 0.46 and 0.66 plants per m2 for cultivars RB867515, RB72454 and SP801816, respectively. Control of B. brizantha was most effective when herbicides were applied on young plants, and half the recommended dose of the mixture of tested herbicides can be used. At late control, when this species has one to four tillers, the herbicide dose must be increased, being the estimated economic optimum dose 90% of the recommended dose. The technological quality showed greater variability among cultivars than among herbicide treatments. Herbicides interfere directly in the production of stems, and indirectly in the production of sugar, and ametryn and sulfentrazone caused higher negative interference. SP803280 was the cultivar that had the lowest susceptibility to the studied herbicides.