Why we should be worried about PCN

Potato cyst nematodes or PCN are a major pest of potatoes. These small parasitic roundworms feed and reproduce on potato roots which can lead to yield losses in excess of 80%, according to SASA. PCN are spread via contaminated soil, water, tubers, people (boots), and farm machinery and are widely controlled by nematicides.

There are two species of PCN in the UK, Globodera pallida and Globodera rostochiensis. The Future Threat of PCN in Scotland Report, which was produced in 2020, highlighted that the area of land infested with G. pallida (then 6200ha) is doubling every 7 years in Scotland. This is a serious cause for concern for the Scottish and UK potato industry because certified seed potatoes (of which in the UK, approximately 70% are grown in Scotland) and bulbs (worth £7million to the economy) can only be grown on land where the soil has been tested and found to have no PCN cysts present by SASA. More land is infested with G. rostochiensis (around 14500ha in 2020), but the area is not increasing as quickly.

If the soil is found to have PCN, it is recorded as infested (‘Scheduled’) meaning no seed potatoes can be grown, and if ware crops are to be grown, an approved control programme which suppresses PCN is required for that area of land. This impacts land owners who may lose out on rental income for PCN-infested potato land as seed can’t be grown, forcing seed growers to move to new production areas. For ware, the impact of decreased yields, the expense of nematicides and rising costs of other inputs could make production unsustainable. PCN will also impact retailers because if less seed can be grown, the ware industry will be affected. Furthermore, the varieties retailers and their customers currently prefer might not be readily available in future, especially if the nematicides needed to protect their yield are removed from the market. Nematicides do not reduce the PCN population so should not be solely relied on to manage PCN.

An integrated pest management system is an effective way to manage PCN. The soil should be sampled to find out if PCN is present or not, and depending what species is found, a resistant variety should be grown to reduce the PCN population. There are currently fewer G. pallida resistant varieties and those that are available, have yet to be fully embraced commercially. Extending the interval between potato crops to 6 years should be considered, or longer, if possible, as this will reduce the PCN burden in soil. However, this has a financial implication for several stakeholders, and the effectiveness of rotations can be reduced by groundkeepers (volunteer potato plants), which also need controlling to manage PCN.

There is little doubt that PCN is a concern throughout the potato industry. Thanks mainly to a working group of industry, government and academic members, the Scottish Government have stepped in and are funding a 5-year project of scientific research and knowledge exchange with the aim of delivering a sustainable potato and bulb industry for Scotland through the management of PCN. Several organisations are working to further develop important areas including integrated pest management, decision support, groundkeeper control and genetic markers.

Jane Brisbane, SAC Consulting