A Model-based Assessment of the Impacts of Climate Variability on Fusarium Head Blight Seasonal Risk in Southern Brazil

The frequency of Fusarium head blight (FHB) outbreaks increased considerably in many countries in the last two decades. We used a crop-disease model to assess the impacts of climate variability over a 50-year period at Passo Fundo, Rio Grande do Sul, Brazil. Thirty individual simulation runs of a wheat model were performed for each year by varying planting dates from 1 June to 30 June. For each simulation, an FHB risk index was estimated with the disease model using the heading date simulated by the crop model. A seasonal FHB risk index was estimated by averaging the 30 indices each year. Our simulation results showed that climate at Passo Fundo became favourable to FHB after the 1980s following a period of less favourable conditions for epidemics in the 1960s and 1970s. The risk for FHB was higher for the later planting dates in the most recent decades. Consideration of sea surface temperature (SST) anomalies (deviations from long-term mean values) in the Tropical Pacific Ocean allowed the separation of groups of years with frequently low FHB risk (negative SST anomalies, La Nina like years) and years with frequently high FHB risks (positive SST anomalies - El Nino like years, and near-normal SST - neutral years). Southern Atlantic SST anomalies were then included to separate years with different FHB risks in El Nino-like years and Neutral years. However, the consideration of these anomalies did not result in an improvement. Our results suggest that increased spring rainfall linked to warm sea surface temperature in the Pacific after the 1980s was associated with higher frequency of FHB epidemics in southern Brazil.