Aplication moment of fungicide pyraclostrobyn + epoxiconazol in soybean rust control

Abstract

Soybean rust, a new disease in Brazil caused by Phakopsora pachyrhizi, occurred in the 2002/2003 crop season in the main producing regions. In order to avoid significant yield losses and unnecessary sprays, it is necessary to determine the better moment to spray fungicide. This work compared different spray moments to control soybean rust, spraying pyraclostrobin + epoxiconazol (0,5 L/ha c.p.) in the following treatments: 1 - sprayed in R4 growth stage; 2 - 4 days after first aplication (DAF); 3 - 9 DAF; 4 -14 DAF; 5 -19 DAF; 6 - 23 DAF; 7 - control (water). The cultivar was Fepagro-RS 10, planted in January 10th of 2003, and set up in randomized blocks, with 4 repetitions. The first lesions of rust were visible 4 DAF, in the control treatment. The yield (kg/ha) and the weight of 100 seeds (g) were measured. The treatments in R4 and, 4, 9, 14, 19 and 23 DAF showed, respectively, 15, 17, 17, 8, 11 and 8% higher yield that control, and 12, 14, 7, 7, 5 and 1% higher weight of 100 seeds that control. The treatments in R4 and 4 DAF were more efficient with no statistical difference between them. Taking a decision-making practical conceming whether to spray the fungicide or not, the treatment 4 DAF would be more suitable because it was performed when the first symptoms appeared in the field.