Temporal Dynamics of Soybean Rust Associated With Leaf Area Index in Soybean Cultivars of different Maturity Groups

Experiments were conducted in Mato Grosso, Brazil, from 2009 to 2011 to evaluate the effects of planting date (October, November, December, and January) on soybean rust (SBR) and leaf area index (LAI) in SBR-susceptible soybean cultivars of different maturity groups (early-maturing, midseason, and late-maturing). Mean relative area under the LAI progress curve (RAULAIPC) was significantly higher (P < 0.05) for the late-maturing than early-maturing and midseason cultivars. The October planting date had significantly higher (P < 0.05) mean RAULAIPC than the December and January planting dates. Mean relative area under the SBR progress curve was significantly lower (P < 0.05) for the late-maturing than the midseason and early-maturing cultivars, and significantly higher (P < 0.05) for the December and January than the October and November planting dates. Based on the logistic population growth model, SBR severity increased over time at a significantly higher mean rate for the early-maturing than the midseason and late-maturing cultivars. It took longer for SBR to reach a certain severity level for the late-maturing cultivar planted in January than the early-maturing cultivar planted in October. This implies that fungicides would need to be applied early to the early-maturing cultivar planted in October to minimize yield loss.