The Nematicide Stewardship Programme (NSP) is urging UK potato growers to consider pre-harvest residue testing of tubers in response to unusually dry weather conditions that may have impacted the degradation of granular nematicides applied at planting.

Low soil moisture levels this season, particularly during spring and early summer, could have reduced the breakdown rate of products such as Nemathorin 10G (fosthiazate), potentially resulting in elevated residue levels in the soil later into the growing season. The risk is particularly acute for growers without access to irrigation or those who limited water use to conserve supplies earlier in the year.

“The NSP has a long history in promoting best practice use and handling of granular nematicides,” said Patrick Mitton, Chair of the Nematicide Stewardship Programme. “The advice being offered for this extremely dry season helps to guide the end-of-season actions of growers in their collective support for the continued use into the future of granular nematicides, such as Nemathorin 10G.”

According to the product label for Nemathorin 10G, adequate soil moisture—either from rainfall or irrigation—is essential at the tuber initiation stage to activate its nematicidal and wireworm control properties effectively. The label further specifies a mandatory minimum interval of 119 days (17 weeks) between application and either haulm destruction or harvest. This interval must be observed regardless of residue test results.

The combination of hot, dry weather and restricted water use could also lead to early senescence or suboptimal tuber bulking, further complicating harvest timing decisions.

“Growers should take a representative sample from the treated area, selecting tubers from multiple plants across the field in a ‘W’ shaped pattern; a sample of at least 2.5kg of tubers should be submitted for testing,” explained independent agronomist Simon Alexander.

Several ISO17025-accredited laboratories in the UK offer residue testing services compliant with Red Tractor Fresh Produce and other assurance schemes. Growers are advised to consult with their agronomists or nematicide suppliers to identify suitable laboratories.

The NSP recommends residue testing in any situation where there is concern over insufficient rainfall or compromised crop growth. The initiative forms part of the industry’s wider efforts to safeguard the long-term use of granular nematicides through adherence to stewardship protocols and regulatory compliance.