Quantitative economic impact assessment of an invasive plant disease under uncertainty – A case study for potato spindle tuber viroid (PSTVd) invasion into the European Union

International treaties require that phytosanitary measures against introduction and spread of invasive plant pests are justified by a science-based pest risk analysis, including an assessment of potential economic consequences. This study evaluates the economic justification of the currently applied phytosanitary measures against potato spindle tuber viroid (PSTVd). It assesses the impact of an unregulated EU infestation, while accounting for uncertainty due to scarcity of data. Expert opinions were elicited to describe the possible range of PSTVd spread. Stochastic simulations, based on the assessments of separate experts, indicated that the direct impacts exceed the costs of current phytosanitary measures (€5.6 M/year) with a probability of 44%, but with large differences between experts making it hard to justify the measures solely by the expected savings in direct impacts. The direct impact on potato producers was estimated with partial budgeting. This impact is 2.1 M€, based on an assumed prevalence of PSTVd of 0.73%, while the direct impact on tomato producers was estimated at 3.5 M€. The total economic impact, considering price changes and higher costs for consumers, was estimated at 4.4 M€ for potatoes and 5.7 M€ for tomatoes. Consumers bore 92% of the total costs of invasion in the case of potato and 77% in the case of tomato. If the presence of PSTVd would imply export restrictions, resulting in an annual loss of more than 1% of the total EU export value of potatoes and tomatoes, the cost of current phytosanitary measures would also be justified. The potential economic impacts of PSTVd into the European Union are therefore demonstrably of importance when considering market effects or export losses but questionable if only accounting for the direct losses. The large degree of uncertainty in the prevalence of disease contributes to the justifiability of measures based on the precautionary principle. The assessment approach can be useful for assessing the economic justification of phytosanitary measures.

► Assessment approach to evaluate economic justification of phytosanitairy measures. ► Economic impacts of an unregulated PSTVd infestation in Europe are estimated. ► Economic impacts compared to costs of phytosanitary measures determines justification. ► Applied PSTVd measures cannot be justified only by expected savings in direct losses. ► PSTVd measures are mainly justified by expected market effects and export losses.