Blight advice from Frontier specialist

“In the short term, crops that are green top lifted may well have a place for fluazinam, but in crops intended for storage where tuber blight has a big impact, its use needs substituting. The use of fluazinam will become more limited overall this year," he predicted.

“As advisors we need to plan how we can effectively substitute for fluazinam and in my view the most important decision comes at the end of the programme where fluazinam was widely used in the past. I think the BASF fungicide, Percos (ametoctradin and dimethomorph), fits well as the last two sprays, as it is compatible with diquat, whereas Raman Top's (cyazofamid) use with diquat needs careful thought. Infinito is another option, but its use can be restricted by end users."

He added: "Percos is one of the few fungicides that has tuber blight on its approved label. If you look carefully at blight fungicide labels, what do they actually say about tuber blight protection. None claim control of tuber blight, though they give advice on reduction of tuber blight.

“We are looking to replace fluazinam use in blight programmes and in trials Percos demonstrated tuber blight reduction equivalent to fluazinam, hence the label claim,” said Dr Morris.

“Percos has tuber blight reduction on its approved label so this is my choice for the last sprays during desiccation with diquat.”

The loss of up to 10 applications of fluazinam from blight programmes means careful planning is now required.

“Percos contains the CAA fungicide dimethomorph and there are restrictions on how many you can use in a programme – up to six in total and no more than three consecutively. So, we have to look backwards to plan our overall strategy.

"For example, if we used two Valbons (benthiavalicarb + mancozeb) and two Presidiums (zoxamide and dimethomorph) and finally two Percos applications during desiccation, that would be the maximum CAAs we are able to use,” he pointed out.

“I would also consider the introduction of the new Corteva Agriscience fungicide, Zorvec Enicade (oxathiapiprolin), from early rapid canopy to help replace the loss of fluazinam. This new product is supplied in a co-pack with Gachinko (amisulbrom) as a resistance strategy for oxathiapiprolin single-site active ingredient.

“The tank-mix of Zorvec Eincade and Gachinko adds different forms of activity against zoospores,” he said. “This is important because trials have shown we must not ignore tuber blight control during rapid canopy as tubers are present from within a few weeks after emergence.”

The UK blight population has changed a lot over recent years. The two dominant aggressive strains 13_A2, resistant to metalaxyl-m, and 6_A1 have now been joined with 37_A2 which is tolerant to fluazinam. “Blight control is a continuing challenge. We need to be aware of resistance management. Sustainable resistance management advises use of sequences of at least four different effective modes of action.

"Percos provides an additional mode of action that is effective against tuber blight," said Dr Morris.

He added that the cold wet winter and late spring had delayed planting, meaning more blight is possible during the establishment phase.

At the other end of the crop’s life, if the crop struggled to reach 100% ground cover, there may be a temptation to keep it in the ground for longer to bulk up. "But this means more tuber blight risk, especially as conditions are more likely to be poor in late lifted crops,” he said.

Paul Goddard, BASF’s potato expert, said that Percos has two actives with different modes of action, which gives it built-in resistance management.

“It is one of the most complete blight fungicides you can get, being able to hit blight at all stages of its life cycle,” added Mr Goddard. “I think growers will find appropriate places in the blight programme at the beginning, in the middle and at the end. But bear in mind it can only be used four times in a programme.”