WITH the evolution of more aggressive genotypes of potato late blight, comes an added need for more robust anti-resistance strategies – with all applications – according to Syngenta’s technical manager, Michael Tait.

A Eurofins trial, in Derbyshire, last year, tested the fungicide activity of blight products in inoculated and irrigated plots, which were also shown to be infected with the aggressive EU36_A2 genotype. This showed that mandipropamid with a drift retardant to be the most effective fungicide against all the blight isolates in the trial.

Mr Tait highlighted oxathiapiprolin was not included in the trial, to fulfil industry commitments to avoid its expose to resistance pressure with season-long intrinsic activity trials.

“The trial results showed that Revus is inherently active on all blight genotypes present, including EU36_A2,” he reported. “The priority to learn from the evolution of more aggressive new isolates is that robust treatments can help protect the efficacy of every application in the programme for season-long control.”

Mr Tait added that whilst the trial had been inoculated with Pink 6_A1; Blue 13_A2 and Green 37_A2, subsequent analysis by James Hutton Institute showed that EU36_A2, which infected naturally, was the dominant late blight genotype in infected plots.

The incidence of EU_36 A2 increased exponentially last season, to 27% of all blight genotypes identified in overall analysis of UK monitoring. That was up from 17% in 2018 and less than 2% when first found in 2017.

“It is now recognised that mixing blight fungicides with different modes of action in with Revus – like mancozeb and other partner fungicides – would provide a technically sound and cost effective option for growers and agronomists, he advocated. The mix also ensures growers can make best use of available CAA fungicide group applications under FRAC guidelines.”

He reminded growers that where CAA fungicides are applied as a mixture, they can be used for up to 50% of the total number of applications per season, to a maximum of six applications.


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