Monitoramento de Phakopsora pachyrhizi como critério para aplicação fungicida na soja e efeito da desfolha artificial na produtividade

Abstract

Soybean productivity is strictly related to photosynthesis generated by the leaf area of the crop, so that factors that culminate in defoliation can affect the crop's production. One of the consequences of the disease, known as Asian soybean rust, is the premature fall of leaves at a high level of severity, from the base to the apex of the plants, with difficult management after the closure of the crop. In this sense, it has been sought to anticipate applications for the vegetative stage of the crop, in order to increase control in the lower canopy of the crop. However, it is still not known about the real importance of the lower dossal in the productive components of the crop and if the criterion for the beginning of fungicidal applications in the vegetative stage is the most appropriate in the management of soybean rust. In this context, the objective of this study was to evaluate the effect of defoliation by the progress of soybean rust and to evaluate the effectiveness of fungicidal applications initiated under different criteria for the control of Phakopsora pachyrhizi. For the defoliation simulation, two methodologies were tested: defoliation by stratification of the canopy and by counting the number of leaflets, in the direction from the base to the apex. These tests were carried out in a completely randomized design in a subdivided plot scheme, with three soybean cultivars (Monsoy 6410, TMG 7063 and Coodetec 202) in the plots, three defoliation stages (V8, R3 and R5) and the defoliation levels in the subplots. 0.33, 67 and 100% defoliation. The variables analyzed were related to the crop yield: number of pods, grains per plant, mass of a thousand grains and productivity. Another experiment was implemented to study the criteria for starting fungicide applications, implanting under randomized block design in sub-divided plots, in the 3x2x8 scheme, with three sowing times (october, november and december), two cultivars (M 6410, TMG 7063 IPRO) and eight criteria for starting fungicidal application: I) control without application, II) vegetative stage - v7, III) reproductive stage R1, IV) seven days after spore detection (DE) via collector, V) 14 DE, VI) 21 DE, VII) 10% of injured leaf area, VIII) 10% incidence. The area under the progress curve (AACP) for lesions and urea was determined, leaf area injured at stage R6, number of pods, mass of a thousand grains (g) and productivity. It was found that the lower canopy is low in terms of soybean crop yield, with defoliation of up to 33% tolerable without damage to productivity. Regarding the criteria for starting fungicidal applications, the treatments with spore monitoring obtained satisfactory results to the control, equaling the standard scheduled protocol, with a reduction in the number of fungicidal applications and greater economic return.