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POSTERS: Chemical control

Management of Phakopsora pachyryzi in Brazil
Elias Zuchelli - Universidade de Passo Fundo. Lucas Rech- Universidade Comunitária da Região de Chapecó, Luiz De Mello- Universidade de Passo Fundo

Phakopsora pachyryzi is the causal agent of soybean rust (SBR). SBR is a major soybean disease in Brazil, damaging yield and increasing production cost, as a result of the four fungicide sprays. However intensive use of single site fungicides has lead to development of resistance. Due to the lack of new chemicals for SBR control, disease management programs must be improve with timing and intervals between sprays, spray rate volume, and use of multisite fungicides. To quantify each factor to improve fungicide efficacy 3 experiments were designed using a fungicide mix of Trifloxistrobin (60g p.c./ha) + Prothioconazole (70g p.c./ha), sprayed four times. Designed in a complete backs randomized. The 1st experiment started sprays at stage R1 and R2 and had 12 and 18 days of intervals to each timing. The 2nd experiment evaluated five fungicide spray rate (40, 80, 120, 160, 200 L/ha). The 3rd experiment evaluated the multisite fungicide Mancozeb (1500g p.c./ha) and Chlorothalonil (1080g p.c./ha). Disease severity and grain yield were evaluated. Data were analyzed using SASMIAgri (p<0.05) and separate by Tukey. Timing and intervals showed yield decrease when spray time was delayed and had 18 day intervals. Fungicide spray rate of 160L/ha had greater yield and less disease severity. Also tank mixture with multisite fungicides increase about 5 bags/ha in yield. These results contribute to SBR program management to avoid further development of resistance.