Background and questions
The potato cyst nematodes Globodera pallida [EPPO code: HETDPA] and Globodera rostochiensis [EPPO code: HETDRO] are regulated in the EU as union quarantine pests and listed as known to occur in the union territory ((EU) 2019/2072).  A new commission implementing regulation sets out the requirements and measures established to eradicate and prevent the spread of G. pallida and G. rostochiensis in the EU ((EU) 2022/1192). In terms of eradication, specific requirements and measures are imposed on infested production sites depending on their intended use. In the case of infected productions sites used for producing potato tubers not intended for planting, the sites shall be subject to an official control programme to prevent further spread of the nematodes ((EU) 2022/1192, Article 8, Point 2). Each Member State can develop their own official control programme but shall, as applicable, take into account a set of elements. One of the listed elements refer to “other agronomic options for pest suppression, as mentioned in point 1 of Annex III to Directive 2009/128/EC”, which in turn contains a list of management options such as crop rotation, use of adequate cultivation techniques (e.g. stale seedbed technique and sowing dates) and use, where appropriate, of resistant/tolerant cultivars.

According to the EU regulation, official re-sampling to revoke the requirement of measures can be done after a minimum period of six years counting from the last potato crop (or last detection of the pest). This period may be reduced to three years if effective (and officially approved) measures have been implemented.

In the context of the general management options listed in Directive 2009/128/EC, the following specific questions were raised by the Swedish Board of Agriculture in relation to potato cyst nematodes:

Q1: How many years without growing potato is required to reduce the nematode population levels significantly?

Q2: Are there any other crops that can increase the efficiency of the crop rotation?

Q3: Is there any data showing how efficient the option of a trap crop is?

Q4: How short should the cultivation cycle for potatoes be, to achieve suppression of the nematode population and to prevent development of vital cysts?

Q5: What strategy should be used when selecting resistant cultivars in the crop rotation in order to decrease the likelihood of developing resistance-breaking populations?

Q6: Several sources state that if a potato cultivar is resistant against the G. rostochiensis pathotype Ro1 it is also resistant against pathotype Ro4. Can this be used in the recommendations for selection of potato cultivars in the Swedish control programme?

Q7: Can it be assumed that a potato cultivar resistant against Ro2 and Ro3 is also resistant to some degree against Ro5, or is specific testing required to decide whether a potato cultivar is resistant against Ro5?

Q8: According to EPPO PM 9/26 the G. pallida pathotype Pa1 is only found on the British Isles in the EPPO region. Is this still correct?

The SLU Risk Assessment of Plant Pests was requested by the Swedish Board of Agriculture to review and analyse the scientific evidence available and provide a summary of the current knowledge in relation to these questions. The report aim to contribute with information relevant for the development of an official control programme of potato cyst nematodes in Sweden.