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Weather the storm of blight pressure

Agronomy Issues
25.06.2019
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Potato blight risk under dark skies

Potato blight pressure has reached high levels for large parts of the country. Combined with the incredibly wet conditions making heavy weather of spraying opportunities, maintaining control has been extremely challenging through a ‘perfect storm’ of infection periods.

This season’s AHDB testing of blight samples has revealed a high proportion of the 36_A2 strain. However, testing has highlighted no resistance and no concerns of insensitivity with any blight products in field situations.

David Cooke - James Hutton Institute

There is no evidence of resistance to any active tested against the 36_A2 blight strain, said Dr David Cooke of JHI

The James Hutton Institute, which undertook a major evaluation of blight strain sensitivity last year, reported: “No evidence of resistance to any active ingredient tested in genotype 36_A2," according to Dr David Cooke (above).

“However, there is a consistent pattern of genotype 36_A2 isolates forming slightly larger lesions than other genotypes across very low doses of all active ingredients tested.”

His advice to growers and agronomists is to maintain current best practice of spray intervals and application rates, utilising a full range of products to follow FRAC Guidelines.

“We would urge more growers and agronomists to register on AHDB’s Fight Against Blight programme and send in blight samples for testing. It will build up an accurate picture of changing populations, to see what is occurring and where,” he advocated.

Syngenta Technical Manager, Michael Tait, added: “All the data currently available shows that REVUS  controls all the known genotypes of late blight.

“Spray intervals have proved a significant challenge with the recent weather conditions, but growers should aim to maintain applications as close as possible according to risk and where spray window opportunities permit,” he urged. "The rapid rainfastness of REVUS will provide reassurance for growers in these situations."

Michael (below) highlighted that for late blight prevention, REVUS should always be applied at the recommended label rate.      

Michael Tait

“Best practice is to alternate or mix REVUS with other effective fungicides from different chemical groups to the CAAs – this advice, for alternation rather than blocking, is relevant to all late blight fungicides.” 

FRAC advice is to use no more than three consecutive products from the Carboxylic Acid Amide (CAA) group, and that they should make up no more than 50% of the overall blight spray programme.  

Registering for BlightCast will give local five-day forecasts of impending blight pressure and spray windows, to enable better proactive decisions on product selection and application timing,” he advised.