Posicionamento de aplicação de fungicidas para controle de ferrugem asiática e produtividade de soja

Abstract

In soybean, Asian rust stands out among the diseases, with chemical control being one of the most used methods to maintain productivity. In cultivars with higher branching, there is a reduction in the contact area of the fungicide, and zero application can bring benefits in controlling the disease. The objective was to evaluate the performance of fungicides in the control of Asian rust, by positioning with and without applications in the vegetative stage of the plant (V0) and the effects on soybean yield. The experiment was carried out in the Experimental Area of the Universidade Federal da Fronteira Sul - Campus Erechim, in the 2022/23 crop season, in a randomized block design, with 4 treatments and 5 replications. The cultivar used was BMX Ativa. The treatments consisted of: T1) control, without application of fungicides; T2) application program with V0; T3 and T4) application programs without V0. The area under disease progress curve – AUDPC, and control (%) of the disease, yield components and crop productivity were evaluated. Between treatments with and without V0 application and Asian rust control there was no difference for AUDPC; the fungicides positioned in the programs provided control of over 91%, also ensuring 19.8% less defoliation. There was no significant difference for the variables number of pods per plant and number of grains per plant. The fungicide application programs with and without V0 showed a higher thousand-grain weight (average of 154.2 g), differing only from the control. As for productivity, the treatments with fungicides did not differ statistically, with the increase in the use of application V0 (T2) in relation to the application program described in T3 being 3.3 sc ha-1 and, in relation to T4, it was 2 sc ha-1 . However, in absolute numbers, T2 stood out in relation to the others, guaranteeing productivity greater than 4,200 kg ha-1 . The late onset of the disease in the area may have contributed to the non-differentiation of the use or not of V0 application. For this reason, the study must be repeated in crop seasons in which there is greater pressure from Asian rust in order to demonstrate the benefit of this application.