Fungos entomopatogênicos associado a adubação no manejo das cigarrinhas das pastagens e promoção de crescimento do capim elefante cv. Roxo

Abstract

Entomopathogenic fungi are bioinputs because they cause the population reduction of several pests without causing damage to the environment and also act as plant growth promoters. In livestock, one of the main pests is the spittlebug in pastures, which requires quick control in order not to affect the feeding of the herd, since the spittlebug injects toxins and dries the pasture. The aim of this study was to evaluate the effectiveness of pasture spittlebugs management in elephant grass (Pennisetum purpureum Schum) cv. Purple and growth promotion, through biometric and physiological parameters, after association between entomopathogenic fungi and fertilization, in the Amazonian rainy season, when spittlebugs attacks occur. The bioassay was conducted in an experimental field at the Federal Rural University of the Amazon - UFRA, in the municipality of Belém. The design was in randomized blocks, with four replications, with the following treatments: T1 – Elephant grass without fertilization (Control), T2 – Grass + fertilization, T3 – Grass + fertilization + Metarhizium anisopliae, T4 – Grass + fertilization + Beauveria bassiana, T5 – Grass + fertilization + Trichoderma asperellum pool. The fungi were inoculated at a concentration of 108 conidia/ml-1. The evaluations were carried out by selecting 1m² in each plot to count the number of foams containing insect nymphs. For the morphological analyzes of the plants and biomass accumulation, the following parameters were evaluated: plant height, stem diameter, number of leaves, robustness index, in addition to fresh and dry matter of the leaves. The physiological variables were net photosynthesis (A), transpiration (E), stomatal conductance (gs), internal CO2 concentration (CI) and carboxylation efficiency (A/CI). The data were submitted to cluster analysis, according to the degree of similarity, resulting in three groups composed as follows: Group 1: (M. anisopliae + fertilization), (B. bassiana + fertilization) and (Pool of T. asperellum + fertilization), group 2 composed by the isolated fertilization and group 3 composed by the negative control, only the grass. Group 1 showed greater gain in morphological and physiological parameters. As for spittlebugs, there was a decrease in the number of nymphs for the treatments: isolated fertilization, M. anisopliae + fertilization, B. bassiana + fertilization, with treatments with B. bassiana and M. anisopliae being the best in relation to the control. Thus, entomopathogenic fungi may be viable alternatives for the preventive management of spittlebugs and growth promoter in elephant grass plants cv. purple.