MANEJO QUÍMICO DE VASSOURINHA-DE-BOTÃO (Spermacoce sp.) NA CULTURA DA SOJA

Abstract

The red-broom (Spermacoce sp.) is a difficult-to-control weed with high infestation in cultivated areas with soybean cultivation in the states of Goias, Piaui, Maranhão and Bahia. Agronomists and producers have reported the difficulty of chemical control of this species, especially when it is in advanced phenological stages at the moment of positioning of herbicides for desiccation in pre-sowing of the summer crop, in which case the broom shows tolerance to the main herbicide used in this operation, the glyphosate. The aim of this work was to evaluate herbicides applied in the pre-sowing of soybeans, isolated and in mixtures, to control the vassourinha-de-botão, and to evaluate the effect of doses of the glyphosate herbicide on the control of the pre-sowing vassourinha-de-botão of the soybean and finally quantify the competitive potential of the vassourinha-de-botão in matocompetition in different population densities on the soybean crop. The experiments were carried out in the field of Santa Barbara Farm, in the municipality of Orizona, Goias State, and the laboratory analyzes were carried out in the Plant Science Department of the Goiano Federal Institute Campus Urutai, in the years 2016 and 2017. The experiments were installed in randomized complete blocks with four replicates, the stand indexes, plant height, number of pods per plant, mass of one thousand grains and productivity were evaluated. The Glyphosate + Carfentrazone + Saflufenacil, Glyphosate + Carfentrazone + Flumioxazin, Glyphosate + Saflufenacil + Flumioxazin mixtures were applied to the pre-sowing, the best weed controls were obtained and consequently the highest yields of the soybean crop. Doses of glyphosate, it was verified that only from 2.880 g and ha-1 there was control of the weed in an early phenological stage. In relation to the matocompetition of the vassourinha-de-botão with soybean, it was observed that from one plant per m² there is a reduction of the mass of 1000 grains and productivity; in competition with six plants of vassourinha-de-botão per m², the reduction in productivity reached 25%. The results allowed a better positioning for chemical control of the vassourinhade-botão and allowed to quantify the losses caused by the weed in the soybean crop.