Blight fungicides that tick all the boxes are like a Holy Grail for potato growers, especially given that new blight strains and late blight are making life difficult for absolute control.

And it’s a long season. Growers need to protect crops from emergence right up to harvest and must also protect tubers from tuber blight, starting from tuber initiation onwards, which is more of an issue as fewer fungicides are able to do this.

Blight strains in the UK have changed radically recently and Dr David Cooke, of the James Hutton Institute, in Dundee, has identified newer strains which are more aggressive, produce more spores from larger lesions and have a faster life cycle. Consequently, effective blight control has become more challenging.

His analysis of late blight samples showed that the most widespread genotype in 2019 was the Strain 6_A1, accounting for 36% of all samples. This declined from 47% in 2018. In 2011, it dominated the UK population with nearly 80% of all samples.

The next most widespread strain last year was 36_A2 which increased from 17% in 2018 to 27% in 2019. The genotype 37_A2 which entered the UK in 2016 is of concern as it is insensitive to fluazinam, which was one of the most widely used fungicides, particularly for tuber blight at the end of the programme.

The phenotype 37_A2 is found mostly in the east of the country, less so in the north or west but has declined from 16% in 2018 to 6% in 2019, perhaps mirroring the drastic reduction in the use of fluazinam and reduction in selection pressure.

The Pesticide Usage Survey in 2014 showed that more than 360,000ha were sprayed with fluazinam, but in 2018 this had gone down to 78,000ha, leaving a significant gap to fill, pointed out Paul Goddard, a potato expert with BASF.

He explained that dimethomorph in both BASF’s Percos and Invader had systemic activity which protected new growth and its translaminar activity which protected the upper and lower surfaces of the leaves.

“Dimethomorph is also well known for its strong antisporulant activity, important in today’s blight market. Percos (dimethomorph and ametoctradin) has tuber blight control on its label, an acknowledgement to its zoospore activity. Having two actives with different modes of action gives Percos and Invader a strong anti-resistance strategy.

“Invader is a combination of dimethomorph and a full rate mancozeb, so you get a strong protectant element, in built anti-resistance strategy plus alternaria (early blight) reduction thrown in for free.”

He added that every year high inoculum from potato dumps or groundkeepers will infect emerging crops.

“Effective systemic fungicides are needed to protect rapidly growing crops from the start. Invader and Percos are able to hit blight at every stage of its life cycle and to control all known blight strains. They are two of the most complete blight fungicides you can get, ticking all the boxes growers are looking for,” said Mr Goddard.

“The active, ametoctradin, has a unique mode of action with no cross resistance and is an ideal anti resistance partner. It also is a non-CAA or QiI/QoI fungicide, giving more flexibility in a programme.

In a sneak preview of what’s coming soon, he said: “In support of our stated strategies, we are developing a number of products for potatoes. We have a new fungicide, coded BAS657, which is a co-formulation with a new multisite active for potatoes. This product out performed all the other products we trialled across the Eurofins and SRUC trials in 2019.

“Its effectiveness has been brought about through careful, advanced formulation chemistry truly enabling the actives to be synergistic. We are anticipating approval in 2021.”

“We also are developing a herbicide for grass and broad-leaved weed control. Growers need a herbicide which is safe to the crop across all soil types and on all varieties. This product is likely to be approved later in 2021, ready for the 2022 crop.”