Modeling of yield Losses and risk analysis of fungicide profitability for managing Fusarium Head Blight in Brazilian spring wheat
Fusarium head blight (FHB), caused by the Fusarium graminearum species complex, is a serious disease of wheat in Brazil. A review of literature on fungicide efficacy for field trials evaluated in Brazil was conducted to obtain FHB-yield data and explore their relationship. Thirty-seven studies (9 years and 11 locations) met the criteria for inclusion (FHB index [≥] 5% and max-min range [≥] 4 percent points [p.p.]). Studies were group into two production situations: low (Yl [≤] 3,631 kg ha-1) or high (Yh > 3,631 kg ha-1) yield, based on the median of maximum yields across trials. Population-average intercepts, but not the slopes, from fitting a random-coefficients model, differed significantly between Yl (2,883.6 kg ha-1) and Yh (4,419.5 kg ha-1). The calculated damage coefficient was 1.05 %-1 and 1.60 %-1 for Yh and Yl, respectively. A crop model simulated attainable wheat yields for 10 planting dates within each year during a 28-year period, including prior (1980-1989) and after (1990-2007) FHB resurgence. Simulated losses using disease predictions to penalize yield were in general agreement in magnitude with literature reports, for both periods. Economic analysis for scenarios of variable fungicide costs and wheat prices, and one versus two sprays of tebuconazole, showed that the probability of not-offsetting the costs was higher (> 0.75) prior to FHB resurgence than after the 1990. Our approach may be useful for designing of longlasting, yet profitable, contingency tactics to management FHB in wheat. Currently one spray of triazole fungicide during flowering is more likely a profitable decision than applying two sprays, for which there is greater uncertainty.