Economic justification for quarantine status – the case study of ‘Candidatus Liberibacter solanacearum’ in the European Union

International agreements on plant health and trade require that regulating a pest should be justified by economic impact assessment. Economic impact assessments are usually qualitative, weakening the objective and transparency of the regulation decision. This study assessed the potential economic impacts of the invasion of the plant pathogenic bacterium ‘Candidatus Liberibacter solanacearum’ into the European Union in order to economically justify a decision on its quarantine status. Direct economic impacts resulting from yield loss in potato and tomato were computed using partial budgeting at a regional scale, while total economic impacts on the potato and tomato markets were computed using partial equilibrium modelling at the EU scale. Annual direct impacts at the most likely infestation level were estimated at €222 m for the whole EU. Uncertainty analysis showed a distribution of foreseeable annual impacts with a 5th percentile of €192 m, and a 95th percentile of €512 m. Increased market prices of potato and tomato resulting from reduced supply were found to increase profits for non‐infested producers and to compensate in part for the production losses of infested producers, with consumers paying for this mitigation of impacts on producers. The expected negative impact on societal welfare at the most likely infestation level is less than the estimated direct impacts, viz. €114 m/year. The potential economic impacts of ‘Ca. L. solanacearum’ in the European Union are demonstrably of major importance. Therefore, a decision to categorize this organism as a quarantine pest is supported.     

Individual-based models in the analysis of disease transmission in plant production chains: An application to potato brown rot

Spread of plant disease in production chains of planting material is a process of great economic importance, but has received little attention from plant disease epidemiologists. Disease control in production chains is therefore often based on rules of thumb and expert judgement by regulatory bodies, rather than on an explicit analysis and evaluation of the epidemiological and economic consequences of alternative strategies. This paper puts forward the idea that individual-based models may be used as a framework to simulate the spread of disease-causing organisms in plant production chains. The “individuals” in this context are the trading units (e.g., batches, lots) of a production chain. The quarantine disease “potato brown rot”, caused by the bacterium Ralstonia solanacearum, is used as an illustrative example. The model simulates the spread of potato brown rot over all potato growing farms and fields in the Netherlands over a chosen time frame. It addresses the relevant infection pathways for this disease in potato production and is spatially explicit.

Model outputs of simulations based on the control strategy as applied in the Netherlands until 2004 are presented. The effects of minor adjustments to this strategy are investigated. The simulations show an irregular pattern of brown rot dynamics in the potato production chain, as is observed in practice. Simulations quantify the relative importance of different infection pathways, and elucidate the effect of testing frequency on these pathways and on the over-all brown rot incidence. The study shows that individual-based modelling (IBM) provides a powerful platform for modelling the epidemiology and impact of diseases in plant production chains. IBM can be effectively used for the analysis, evaluation and design of cost-effective disease management policies.     

Evaluation of different procedures to interpolate particle-size distributions to achieve compatibility within soil databases

Many environmental and agricultural problems are not restricted to national boundaries and therefore require international cooperation if solutions are to be found. Often, these solutions require the ability to use soil data as input in simulation models, however, despite a number of recognised international standards, soil data are rarely compatible across national frontiers. This problem was encountered when creating the draulic operties of uropean oils (HYPRES) database. The data, which includes particle-size distributions, were collected from 20 institutions in 12 countries. Only a few of these institutions adhered strictly to a recognised international system. Therefore, interpolation of the cumulative particle-size distribution was required to achieve compatibility of particle-size distributions within the HYPRES database. In this study, four different interpolation procedures were evaluated. The accuracy of the different procedures was found to vary with size intervals between measured points of the particle-size distribution. The loglinear interpolation of the cumulative particle-size distribution has previously been used in various studies but was found to give the least accurate estimation of the four procedures. Fitting the Gompertz curve, which is a special asymmetric type of curve described by a closed-form equation, showed less sensitivity to size intervals between measured points. However, interpolation within some of the particle-size distributions was not sufficiently accurate and this procedure could not be applied to particle-size distributions where the number of measured size fractions was less than the number of model parameters. Fitting a nonparametric spline function to the particle-size distributions showed a considerable increase in accuracy of the interpolation with decreasing size intervals between measured points. As a novel approach, the similarity procedure was introduced which does not use any mathematical interpolation functions. It uses an external source of soil information from which soils are selected with particle-size distributions that match the distribution of the soil under investigation. This similarity procedure was capable of giving the most accurate interpolations. Once an extensive external reference data set with well-quantified particle-size distributions is available, the similarity procedure becomes a very powerful tool for interpolations. Based on the number and distribution of measured points on the particle-size distributions, a general rule was formulated to decide whether to fit a spline function or use the novel similarity procedure to estimate missing values. Results of this study were used to classify all soils in the HYPRES database into the same soil texture classes used in the 1:1.000.000 scale Soil Geographical Database of Europe.     

Adaptation to climate change and climate variability in European agriculture: The importance of farm level responses

Climatic conditions and hence climate change influence agriculture. Most studies that addressed the vulnerability of agriculture to climate change have focused on potential impacts without considering adaptation. When adaptation strategies are considered, socio-economic conditions and farm management are often ignored, but these strongly influence current farm performance and are likely to also influence adaptation to future changes. This study analysed the adaptation of farmers and regions in the European Union to prevailing climatic conditions, climate change and climate variability in the last decades (1990–2003) in the context of other conditions and changes. We compared (1) responses in crop yields with responses in farmers’ income, (2) responses to spatial climate variability with responses to temporal climate variability, (3) farm level responses with regional level responses and (4) potential climate impacts (based on crop models) with actual climate impacts (based on farm accountancy data). Results indicated that impacts on crop yields cannot directly be translated to impacts on farmers’ income, as farmers adapt by changing crop rotations and inputs. Secondly, the impacts of climatic conditions on spatial variability in crop yields and farmers’ income, with generally lower yields in warmer climates, is different from the impacts of temporal variability in climate, for which more heterogeneous patterns are observed across regions in Europe. Thirdly, actual impacts of climate change and variability are largely dependent on farm characteristics (e.g. intensity, size, land use), which influence management and adaptation. To accurately understand impacts and adaptation, assessments should consider responses at different levels of organization. As different farm types adapt differently, a larger diversity in farm types reduces impacts of climate variability at regional level, but certain farm types may still be vulnerable. Lastly, we observed that management and adaptation can largely reduce the potential impacts of climate change and climate variability on crop yields and farmers’ income. We conclude that for reliable projections of the impacts of climate change on agriculture, adaptation should not be seen anymore as a last step in a vulnerability assessment, but as integrated part of the models used to simulate crop yields, farmers’ income and other indicators related to agricultural performance.     

The impact of the quality of silage on animal health and food safety: a review

This paper reviews the microbiological aspects of forage preserved by ensilage. The main principles of preservation by ensilage are a rapid achievement of a low pH by lactic acid fermentation and the maintenance of anaerobic conditions. The silage microflora consists of beneficial micro-organisms, i.e. the lactic acid bacteria responsible for the silage fermentation process, and a number of harmful micro-organisms that are involved in anaerobic or aerobic spoilage processes. Micro-organisms that can cause anaerobic spoilage are enterobacteria and clostridia. Clostridium tyrobutyricum is of particular importance because of its ability to use lactic acid as a substrate. Silage-derived spores of C. tyrobutyricum can cause problems in cheese making. Aerobic spoilage of silage is associated with penetration of oxygen into the silage during storage or feeding. Lactate-oxidizing yeasts are generally responsible for the initiation of aerobic spoilage. The secondary aerobic spoilage flora consists of moulds, bacilli, listeria, and enterobacteria. Mycotoxin-producing moulds, Bacillus cereus, and Listeria monocytogenes in aerobically deteriorated silage form a serious risk to the quality and safety of milk and to animal health.     

Interceptions of harmful organisms during import inspections of cut flowers in the Netherlands: an empirical and theoretical analysis of the ‘reduced checks’ system*

As of January 1st 2005, a system of reduced checks for phytosanitary inspections of certain plants and plant products imported into the European Union (EU) is in place. Under this system, plants and plant products satisfying special criteria may be inspected with a reduced frequency. These criteria are based on EU‐wide data on historical volumes of import and interceptions of harmful organisms in particular products. The objective of this paper is two‐fold. Firstly, the paper analyses whether proportions of interceptions of harmful organisms associated with cut flowers imported into the Netherlands – the largest EU importer of cut flowers – support the application of reduced checks for certain genera and trades (commodity‐exporting country combinations) of cut flowers. Secondly, the paper analyses how effective the reduced checks system is in minimizing the expected costs of introduction of harmful organisms in the EU. For that, a theoretically optimal system for allocating inspection effort to commodities is described. Using an illustrative example and stochastic simulations, the expected costs of introduction of harmful organisms under the theoretically optimal system and the current system of reduced checks are compared. Examination of interceptions of harmful organisms supports application of reduced checks for most genera and trades of cut flowers in the Netherlands. The results of stochastic simulations show that reduced checks may not minimize the expected costs of introduction of harmful organisms into the EU. Accounting for possible economic impacts of harmful organisms in determining the frequencies of reduced checks may help optimize the current system.