Profitability of fungicide applications for managing soybean rust in scenarios of variable efficacy and costs: A stochastic simulation

Soybean rust (SBR) in Brazil is controlled with fungicides, which have shown variable, sometimes declining, efficacy over time. A Monte Carlo simulation framework was implemented as a decision tool and to estimate the probability for fungicide programme being profitable depending on total cost defined by user. Probability distributions were fitted slopes intercepts of disease–yield relationship severity untreated plots reported literature, well historical records soybean price. Simulations disease reduction conditioned predefined control application costs split into scenarios that combined two categories (high low) attainable yield classes low). These based median (57.8%) intercept (yield when zero, 2995.1 kg/ha). matrices constructed relating costs. higher frequency break-even events occurred high pressure yield. Yearly simulations, starting 79.4% efficacy, assuming rates decline previously determined tebuconazole rate), showed may remain during first 5 7 years use, contrast cyproconazole (low would be entire decade. This approach useful can adapted other diseases crops, long damage functions are available. An interactive web app developed perform simulations accessible at alvesks.shinyapps.io/rusty-profits/.