Phenylamide blight resistance increases in potatoes

Blight testing that found higher levels of resistance to phenylamide blight fungicides, has resulted in Syngenta temporarily reducing the number of Fubol Gold applications recommended during rapid canopy growth to one.

All of the A2 strains tested by Syngenta from blight samples collected during the British Potato Council‘s “Fight against Blight” campaign were the so-called “blue-13” strain, the firm’s Simon Parker says. “Numbers tested were small but all of them were resistant to phenylamide blight fungicides.”

The blue-13 A2 strain was found to be the dominant blight strain in the UK population by a BPC-funded study last year, when 82% of blight population was the A2 type.

But the Syngenta findings do not necessarily mean all blue-13 A2 blight is resistant, Mr Parker says. “There have been cases in France where blue-13 blight is not resistant.”

The increased level of resistance could have been associated with the sustained blight pressure from early season onwards, says Beth Hall, Syngenta technical manager.

However, results from blight trials suggest Fubol Gold continued to perform well last season, she claims. “But growers must be prepared to adopt further anti-resistance strategies to counter the resistance threat.”

For the coming season Syngenta has reduced the number of Fubol Gold applications to one. But the firm will be attempting to capture the earliest cases of blight on crops emerging from under plastic and other early crops to determine whether the two-spray approach can be reinstated.

Previous research has suggested the proportion of phenylamide-resistant strains declines over winter. “We need to assess the blight population in the early spring this year to identify the level of resistance remaining in the population and the risk to crops. Until then, growers should proceed with caution and ensure Fubol Gold is followed with fungicides with an alternate mode of action.”