Silício na produtividade e no controle da cigarrinha-das-raízes Mahanarva fimbriolata Stal em cana-de-açúcar

Abstract

The advent of automated sugarcane harvesting, and its replacement of traditional pre-crop burning, has created a favorable environment for the spittlebug Mahanarva fimbriolata Stål. The spittlebug was previously considered a problem just in the sugarcane plantations of northeast Brazil, but it has now become one of the main problems for this culture in the South-central region. Silicon has been shown to be capable of inducing resistance of plants to pathogens and insects. The objectives of this work were to evaluate the effect of Silicon on the productivity and improvement of the technologically measured quality of sugarcane, as well as on the control of the spittlebug in this culture and also to compare the effects of chemical treatment, biological treatment and silicon application on the population of this pest, on the natural biological control of this insect by entomopathogenic fungus and on the population of some non-target arthropods in this culture. Two experiments were installed and conducted on cultivar SP80-1816 at a commercial sugarcane production area owned by Guaíra Sugar Meal, in Guaíra-SP. The experimental delineation was in randomized blocks in factorial outline 8x9x5 (eight treatments, nine sampling dates and five repetitions) for the populations of spittlebugs, spittlebugs killed by entomopathogenic fungus and some arthropods; and in randomized blocks, with eigth treatments and five repetitions, for other variables. The treatments were, Control; 8,2 L ha-1 of potassium silicate (one application), 16,4 L ha-1 of potassium silicate (two applications of 8,2 L ha-1), 24,6 L ha-1 potassium silicate (three applications of 8,2 L ha-1), 1000 kg ha-1 calcium and magnesium silicate, 0,8 kg ha-1 of the insecticide thiamethoxan 250 WG, 4,0 kg ha-1 of the biological insecticide Metarhizium anisopliae (sporulated rice) and 4,0 kg ha-1 of M. anisopliae (wettable powder). Between November 2005 and February 2005 samplings were made of the spittlebugs, spittlebugs killed by entomopathogenic fungus and some arthropods. The analyses of the technological parameters and evaluation of the productivity of the sugarcane were made one year after the installation of the experiments. Increases of 105,40%, 117,59% and 124,50% in the productivity of the sugarcane were verified with two and three applications of 8,2 L ha-1 potassium silicate and 1000 kg ha-1 of calcium and magnesium silicate, respectively, in one of the experiments. It was concluded that there was higher sugarcane productivity with the application of Si in the area with a lower amount of this element in the soil; there were increases in sugarcane productivity with the chemical and biological application of insecticides for the control of the spittlebug; the chemical and biological treatments and potassium silicate in two foliar applications presented the same performance in the control of this insect and the chemical and biological treatments in both formulations and the application of Si did not affect the natural biological control of the spittlebug by the entomopathogenic fungus and the population of the arthropods in sugarcane.