Bio-economic modelling of brown rot in the Dutch potato production chain

Brown rot, a quarantine disease caused by Ralstonia solanacearum race 3, biovar 2, comprises a major threat to the Dutch potato production chain. To avoid export losses, the Dutch government has implemented a costly control policy. However, it is unknown whether this policy is optimal from a cost-effective point of view. This thesis describes the development of a bio-economic model that can be used to evaluate the cost-effectiveness of brown rot control policies in the Netherlands. Two conceptual epidemiological models, a state-variable model and an individual-based model (IBM), were developed and compared for their suitability to model brown rot dynamics within the potato production chain. The IBM was selected for further development into a spatially explicit epidemiological model. Applications of this model illustrated how it can enhance insight into brown rot dynamics within the Dutch potato production chain. The epidemiological model was integrated with an economic model into a bio-economic model, which quantifies the costs and benefits of a control strategy on the basis of its effect on brown rot incidence in the chain. Model applications showed amongst others that export losses are of decisive importance in determining the cost-effectiveness of a control policy, and that conclusions on the costeffectiveness are affected by the period over which the effect of a policy on brown rot dynamics is observed. Results of an impact analysis of model parameters on the incidence and economic consequences of brown rot revealed that policy and sector factors in particular have a large impact on the cost-effectiveness of control, while exogenous and economic factors are of lesser importance. Scenario studies based on the results of the impact analysis indicated that highly cost-effective control requires cooperation of the government and sector. The research described in this thesis shows that bio-economic modelling can facilitate the design and implementation of optimal brown rot control policies, by (1) enhancing insight into the incidence and economic consequences of brown rot in the potato production chain, (2) enabling ex ante evaluation of control strategies for their cost-effectiveness, and (3) enabling objective communication on brown rot control towards the sector. The modelling approach and the general insights obtained in this research are applicable to other quarantine diseases as well.