Plan blight control to reduce resistance risk

Potato growers are urged to plan their anti-resistance strategies for blight following the failure of a major control product.

Total control failure in potato blight management product mandipropamid (Revus) was confirmed in Europe last December – prompting warnings that British farmers must revise their own strategies too.

The resistant blight genotype (EU43) is yet to be identified in the UK – but growers were told to act now to protect potato crops because blight strains that start in Europe inevitably make their way over here, says Geoff Hailstone, potato lead at UPL UK.

“Farmers need to plan their blight control programmes carefully,” he warns. Resistance was confirmed in a joint study by leading agri-chemical companies and researchers from Aarhus University, Denmark.

While a concern, blight resistance to fungicidal products is not a novel situation for UK growers. Lessons have been learnt as a result of previous fungicide resistance issues, says Mr Hailstone.

Responsible approach

“The UK has a robust blight monitoring programme and a responsible approach to control. British producers still have plenty of options to choose from, but solo product applications must be avoided.”

Instead, growers should consult their agronomists about product mixing. “The advice should be to mix blight control products with at least one active ingredient from another group. And with each application, mixes need to be alternated.”

Growers should be mindful that all carboxylic acid amide (CAA) group fungicides, of which mandipropamid is one, could  pose a threat because there is a cross-resistance risk between CAA products.

CAA group products contain dimethomorph, benthiovalicarb, or mandipropamid, says Mr Hailstone. “We need to monitor these fungicides, as there may be additional losses from this product group.”

A prudent approach would be to consider mixing single-site products like mandipropamid with a multi-site product like Manzate 75 WG (mancozeb) or using Proxanil (propamocarb + cymoxanil) which contain actives from low-resistance-risk groups.

Later in the season, Proxanil + Ranman Top (cyazofamid) are rated most effective on the Euroblight table to control tuber blight and avoid issues in storage.