Probabilistic economic analysis of a weather-based adaptive disease management strategy-the case of myrtle rust in New Zealand nurseries

In agricultural systems, responsive management can mitigate the effects of risk and uncertainty by facilitating adaptation to changing conditions. A tool for evaluating management systems while accounting for risk and uncertainty is Probabilistic Cost Benefit Analysis (PCBA). This study used PCBA to contrast a new responsive disease management strategy against an existing prescriptive strategy. Fungicide application to prevent myrtle rust (MR) in NZ plant nurseries was used as a case study to test if the expected benefits of a responsive strategy such as avoided incursions, justified the investment in potentially more frequent and costlier control. A stochastic MR risk generator was developed and used to simulate disease incursion reflecting variable weather. Using the stochastic generator, empirical distribution functions of net benefits were estimated and compared across scenarios highlighting the potential impact of infrequent but substantial disease impacts. Our results showed that the risk-based strategy was more effective at controlling the disease, especially for myrtle plant species that are highly susceptible in high-risk locations. The findings highlighted the essential role of fungicides in the cultivation of highly MR-susceptible species, and that disease management that is responsive to risk enhanced the efficiency of fungicide use. Responsive fungicide strategies are discussed as an effective management option for nursery managers, and the wider implications of responsive management for maintaining the robustness of agricultural systems are considered.