EFFICIENCY AND ECONOMIC VIABILITY OF APPLICATION OF FUNGICIDES IN THE CONTROL OF ASIATIC RUST OF SOYBEANS IN CAMPO GRANDE, MS, BRAZIL

ABSTRACT

The present study evaluated the efficiency and the economic viability of the application of fungicides to control Asian soybean rust, Phakopsora packyrhizi, in Campo Grande, state of Mato Grosso do Sul, Brazil. The assay was carried in the 2007-2008 harvest. The following fungicides were evaluated (g a.i./ha): picoxystrobin + cyproconazol (40 + 16, 50 + 20 and 60 +24) + nimbus 0.25% (v/v); pyraclostrobin + epoxiconazol (66.5 + 25); azoxystrobin + cyproconazol (60 + 24) + nimbus 0.25% (v/v); trifloxystrobin + tebuconazol (50 + 100) + auero 0.13% (v/v) and trifloxystrobin + cyproconazol (56.25 + 24) + aureo 0.13% (v/v). The fungicide treatments started from the phenologic stage R2. Three applications were realized, 15 days apart. The disease severity (upper and lower part of the plant) was quantified weekly, totaling 10 evaluations. In addition, at the R7 stage, the defoliation was evaluated every seven days. The curves of progress (CP) were plotted and calculated the areas under the CP for the disease severity (AACPD) and defoliation (AACPDes). At the end of the assay, the grain yield (Rend - kg/ha), the mass of 1,000 grains (MMG - g) and the economic viability of the disease control were evaluated. The climate during the conduction of the experiment was favorable to the development of Asian soybean rust. There was a positive relationship between rainfall and severity of the disease. All fungicides showed AACPD below the control, especially picoxystrobin + cyproconazol (higher fungicide dose). This treatment also showed the lowest rate of AACPDes. The fungicides presented similar rates of Rend, although higher than the control treatment. In relation to MMG, the highest index was attributed to azoxystrobin + cyproconazol. The mixture trifloxystrobin + tebuconazol showed the lowest efficiency for the control of Asian soybean rust. Based on the severity of the disease, grain yield and the economic benefits generated by the application of fungicides, picoxystrobin + cyproconazol (60 + 24), azoxystrobin + cyproconazol and trifloxystrobin + cyproconazol were identified as the most promising for the control of P. packyrhizi.

KEY WORDS  Phakopsora pachyrhizi ; Glycine max ; chemical control