Potato growers are being advised to carry out pre-harvest residue testing following this year’s prolonged dry conditions, which may have left higher-than-expected levels of granular nematicide in the soil.
The Nematicide Stewardship Programme (NSP) has issued fresh guidance urging farmers to assess the risk of residue in their crops—particularly where granular nematicides such as Nemathorin 10G (fosthiazate) were applied at planting.
Dry soil conditions during spring and early summer may have hindered the usual breakdown and movement of nematicides through the soil profile.
This is especially relevant for growers with limited irrigation or those who have conserved water earlier in the season.
A lack of rainfall can reduce tuber bulking and lead to early senescence, both of which could impact crop quality and harvest timing.
Dr Alison Warrington, NFU senior plant health adviser, stressed the importance of following label guidelines and managing product use carefully in such seasons.
The Nemathorin 10G label highlights the critical role of soil moisture—whether from rain or irrigation—during tuber initiation.
It also mandates a minimum 119-day interval between application and harvest, which must be observed regardless of any residue test outcomes.
Patrick Mitton, chair of the NSP, backed the move: “The NSP has a long history in promoting best practice use and handling of granular nematicides.
"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.”
Growers concerned about insufficient rainfall or stressed plant development are being advised to conduct a pre-harvest residue test.
Independent agronomist Simon Alexander recommends a thorough sampling approach: “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.”
Testing must be conducted by ISO17025-accredited laboratories to meet requirements under the Red Tractor Fresh Produce scheme and similar assurance standards.
Growers can access further guidance in the NSP best practice guidelines or via Syngenta’s Nemathorin Stewardship Centre.
