Potato Review

32 POTATO REVIEW MAY/JUNE 2020 BLIGHT A s reported previously in Potato Review, blight control has become more challenging owing to changes in strains, with Dr David Cooke of the James Hutton Institute in Dundee identifying newer strains which are more aggressive, produce more spores from larger lesions and have a faster life cycle. Controlling late blight (Phytophthora infestans) in potatoes has become much more complicated. Growers and agronomists have to think about many factors - Paul Goddard, potato expert fromBASF, stressed that the fungicidemode of action, its movement within the plant, and its curative and protectant activities all need careful consideration, at each growth stage of the crop. Paul said that dimethomorph in Percos and Invader, both BASF products, has systemic activity which protects new growth and its translaminar activity, which protects the upper and lower surfaces of the leaves. “Dimethomorph is also well known for its strong antisporulant activity, important in today’s blight market,” he said. Having two actives with di erent modes of action provides a strong anti- Having two actives proves strong anti-resistance strategy BASF is working on developing a number of new products for potatoes to provide protection from emergence to harvest, and has issued new advice on late blight control. resistance strategy in Paul’s view, pointing out that Percos contains dimethomorph and ametoctradin while Invader is a combination of dimethomorph and a full rate mancozeb. Dr Cooke’s analysis of late blight samples showed that the most widespread genotype in 2019 was the Strain 6_A1, accounting for 36% of all samples. is declined from 47% in 2018. In 2011 it dominated the UK population with nearly 80% of all samples. e next most widespread strain last year was 36_A2 which increased from 17% in 2018 to 27% in 2019. e genotype 37_A2 which entered the UK in 2016 is of concern as it is insensitive to uazinam, which was one of the most widely used fungicides, particularly for tuber blight at the end of the programme. e 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 uazinam and reduction in selection pressure. Paul says that every year high inoculum from potato dumps or groundkeepers will infect emerging crops. “E ective systemic fungicides are needed to protect rapidly growing crops from the start of the programme. Invader and Percos are able to hit blight at every stage of its life cycle and to control all known blight strains. ey are two of themost complete blight fungicides you can get, ticking all the boxes growers are looking for,” said Paul. “ e active ametoctradin has a uniquemode of actionwith no cross resistance and is an ideal anti resistance partner. It also is a non CAA or QiI/QoI fungicide givingmore exibility in a programme. BASF’s focus on new products has included a new fungicide, coded BAS657, which is a co-formulation with a new multisite active for potatoes. Paul said the product out- performed all the other products trialled across the Euro ns and SRUC trials in 2019. “Its e ectiveness has been brought about through careful, advanced formulation chemistry truly enabling the actives to be synergistic. We are anticipating approval in 2021,” he said. “We are also 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. is product is likely to be approved later in 2021, ready for the 2022 crop.” The crop treated with the new blight product beside the untreated which has been devastated by blight. This photo was taken by Dr Ruairdh Bain at SRUC last year. “The active ametoctradin has a unique mode of action with no cross resistance and is an ideal anti resistance partner.”