Nível de dano econômico da Conyza spp. em áreas de produção de soja

Abstract

Among the main weeds that occur in the soybean growing areas of the western region of Paraná, the Conyza genus is among the most predominant, mainly due to the continuous applications of the same mechanisms of action of herbicides, and the result has been great losses in productivity. Thus, the objective of this work was to evaluate the economic damage level of Conyza spp. in soy production areas in western Paraná. The experiment was carried out under field conditions in the 2018/2019 summer harvest, in 13 commercial soybean production areas located in the municipalities of Toledo (areas 1 and 2) Maripá (areas 3 to 7), Ouro Verde do Oeste (areas 8 and 12) and Medianeira (area 13), in the State of Paraná. Each area the treatments referring to the densities of Conyza spp. were randomly allocated, according to population levels found naturally in the areas, corresponding to 0, 1, 2, 3 and 4 plants m-2, with four replications per density. Weed managements were grouped in different ways, as follows: management 1 - (areas from 1 to 4) pre-sowing desiccation - 30 DAS with glyphosate + 2,4-D / paraquat and post-emergence glyphosate + clethodim; management 2 - (area 2) pre-sowing desiccation - 30 DAS with paraquat and postemergence glyphosate + cloransulam; management 3 - (areas 6 and 7) pre-sowing desiccation - 30 DAS with glyphosate + 2,4-D + chlorimuron/ paraquat or glyphosate + chlorimuron / paraquat and post emergence glyphosate; management 4 - (areas 8 and 9) pre-sowing desiccation - 30 DAS with glyphosate + saflufenacil and postemergence glyphosate + haloxyfop or only glyphosate; management 5 - (areas 10 to 12) without pre-sowing desiccation - 30 DAS and post-emergence glyphosate + clethodim or glyphosate + haloxyfop; management 6 - (area 2) without pre-sowing desiccation - 30 DAS and without post-emergence application. The coexistence of soybean plants with Conyza spp. promoted reductions in the order of 1.6 g to 4.6 g per plant m-2 in the mass of a thousand grains between areas 1, 4, 5, 6, 11, 12 and 13 depending on the management used, in areas 2, 3, 7, 8 and 9 it was not possible to define the losses. The reduction in grain yield due to the increase in the density of Conyza spp. was verified in 11 of the 13 evaluated áreas, in areas 4 (management 1) and 10 (management 4) there was no effect of increasing the density of Conyza spp. in productivity, a fact that may have occurred due to management or local conditions. Thus, the presence of 1 plant m-2 of Conyza spp., caused reductions in grain yield from 20.90 to 377.85 Kg ha-1. Considering the average economic values used during soybean cultivation for the 2018/2019 harvest, in which productivity varied between 1410 and 3315.2 Kg ha-1, the grain price ranged from R$ 45 to 90 and the cost of control varied between 0 and R$ 310.10, it was possible to estimate the NDE from 0.25 to 2.31 plants m-2 of Conyza spp. for areas in the western region of Paraná.