The objective of this work was to quantify the yield loss caused by Asian soybean rust in three cultivars sown in different periods in the western region of Bahia. The experiments were installed in São Desidério, BA, in the growing seasons 2007/2008 and 2008/2009. The experimental design was carried out in random blocks with four replicates and subdivided plot scheme in time. The plot was represented by the rust control treatments (with and without chemical control) and the subplots represented by cultivars (Monsoy 8411, BRS Corisco and BRS Barreiras). The severity, number of leaves throughout the cycle and yield were evaluated. The logistic model was the one that better fitted the severity data whereas the polynominal exponential function Ln (y) = a + bx1, 5 + cx0,5 fitted the temporal variation of number of leaves better. The means of the area under the disease progress curve and yield were compared by Tukey test. Yield loss increased during later sowing periods due to greater inoculum pressure hindering disease control and decreasing grain yield.
Glycine max; Phakopsora pachyrhizi; yield