Energy-based threshold for soybean target spot management under climate change in Brazil
Soybean is one of the most important crops for global food security, and understanding the impacts of plant diseases on its productivity is essential, particularly under climate change. Among these diseases, soybean target spot ( Corynespora cassiicola ) has re-emerged as a significant constraint in Brazilian production systems. Current management strategies focus exclusively on yield preservation without accounting for the fossil energy consumed by intensive fungicide use, highlighting the need for an energy-based threshold. Because climate change alters the environmental conditions essential for pathogen development, it is critical to determine whether future scenarios will exacerbate or constrain disease severity, as this directly dictates the frequency of energetically justifiable interventions. This study assessed the future energetic feasibility of chemical control by integrating an epidemiological model with the CROPGRO-Soybean crop model (DSSAT) across 24 Brazilian locations, using five CMIP6 models under three emission scenarios (SSP1-RCP2.6, SSP3-RCP7.0, and SSP5-RCP8.5). Yield losses were converted into energy losses and compared with the energy required for fungicide manufacture and application, establishing the Energy Injury Level (EnIL). The EnIL acts as an energy-based decision threshold, justifying chemical control only when the energy preserved in crop yield surpasses the total energy invested in fungicide interventions. Results indicate that median energy losses decrease across most scenarios toward the end of the century, suggesting a gradual reduction in average disease pressure. However, maximum potential damage increases in the Central and South regions, indicating that severe epidemics may still occur. Consequently, the frequency of energetically justified fungicide applications declines over time. In practice, the EnIL framework provides a tactical tool to help stakeholders optimize fungicide programs, reducing fossil energy waste while ensuring interventions are sustainable under variable future climates.