Fungicide application on soybean plants based on the detection of Phakopsora pachyrhizi uredospores

In order to establish the adequate timing of fungicide application in the management of Asian soybean rust (ASR), the spraying of epoxiconazol and pyraclostrobin fungicide (EPF) was evaluated based on the detection of Phakopsora pachyrhizi (PP) uredospores in field conditions at the research farm of Faculdade Integrado de Campo Mourão, in the state of Paraná, in the crop season of 2009/2010. The experimental design was performed in randomized complete blocks with four replications composed by: 1) EPF application with humidity higher than 80%; 2-5) EPF application 1-2, 6-7, 11-12, and 18-20 days after the first detection of PP spores, respectively; 6) EPF application after the first detection of ASR symptoms; 7) EPF application in the R1 stage. Control was constituted by plants not treated with EPF. There was reduced ASR severity in all treatments. The values of the area under ASR progress curve (AUASRPC), rate of disease progress (r), and maximum severity (Ymax) in control were 520.31, 0.06, and 45.65%, respectively. The lowest values of AUASRPC (39.73), r (0.02), and Ymax (3.91%) were found in treatment 1. Nevertheless, the higher number of EPF spraying was carried out in this treatment with four applications. On the other hand, there were two applications in treatment 4. The lowest yield was recorded in control (2085 kg. ha-1). The highest yield was obtained in treatments 1, 2, 3, 4, 6, and 7, being higher than 3000 kg/ha. Furthermore, the lowest value of the thousand grain weight was estimated in control. The highest values were estimated in treatments 1, 2, 3, and 6. Therefore, the timing of fungicide application based on the detection of PP uredospores is efficient in the ASR management.