Potato growers are being urged to should make strategic soil sampling a priority before lifting harvest to improve long-term control of potato cyst nematode (PCN) in the following crop.
PCN remains one of the most damaging pests affecting UK potato production. Effective control depends on integrated pest management (IPM), with soil testing providing the foundation for informed decisions on variety choice, rotations and crop protection.
Simon Alexander, an independent agronomist and member of the Nematicide Stewardship Programme (NSP) group, said growers should focus on understanding what lies beneath the surface rather than relying on assumptions.
Sampling accuracy
“Soil testing gives you the information needed to make informed decisions, but it is important not to interpret PCN figures too literally,” says Mr Alexander.
Laboratory reports usually provide cyst numbers per 100g of soil and egg numbers per gramme of soil. It is important to understand the difference. Egg counts indicate the current pest burden. Cyst numbers reflect historical PCN activity.
Mr Alexander also warns against treating a laboratory result of “none found” as evidence that PCN is absent. “A 200g sample per hectare is only a handful of soil, so the overall chance of missing eggs or a PCN hotspot is significant,” he says.
More detailed sampling improves confidence in the results. Reducing the sampling area from one hectare to half a hectare doubles the number of sampling points and provides a clearer picture of pest distribution.
“The more detailed your sampling, the better your understanding of how PCN is distributed and the more information you have to shape your management plan.”
He also recommends testing fields two years before potatoes are due to be planted. That gives growers more time to adapt rotations, select suitable varieties and consider additional control measures. Identifying the PCN species is becoming increasingly important. Knowing whether Globodera pallida or Globodera rostochiensis is present can influence variety selection and wider IPM planning because resistance varies between species.
Once results have been assessed, growers can decide whether cultural measures such as trap crops or biofumigation are appropriate. They can also assess whether granular nematicides containing fosthiazate, including Syngenta’s Nemathorin, have a role within the overall strategy.
Where PCN pressure is low, resistant varieties may provide sufficient protection without the need for granular nematicides. However, soil type, field history and expected variety performance should also be considered.
“If PCN levels are very high, it is worth asking whether potatoes should be grown in that area at all,” adds Mr Alexander.
Practical guidance
Where nematicides are used, growers should seek advice from a BASIS-qualified agronomist to ensure products are used appropriately and as part of an integrated programme.
“Understanding your PCN pressure has never been more important. PCN control is not simply a planting-season decision. It starts with knowing what is in the soil today and using that information to build a more resilient plan for the years ahead.”
Updated guidance on the safe and effective application of granular nematicides is available through the stewardship programme to help maximise product performance and support responsible PCN management. The NSP is also encouraging growers to review the latest Code of Good Practice before planting crops. It can be found on the NSP Stewardship website at nspstewardship.co.uk.