Controlling late blight (Phytophthora infestans) in potatoes has become much more complicated. Growers and agronomists have to think about many factors, including disease pressure, blight strains, growth stage of the crop, weather conditions, fungicide mode of action, movement of the fungicide within the plant, resistance management, and many more.
Growers need to protect their crops from emergence right up to harvest. They must also protect tubers from tuber blight, starting from tuber initiation onwards, 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 over 360,000 hectares of fluazinam were sprayed. In 2018 this has gone down to 78,000 hectares, leaving a significant gap to fill in the programme, says Paul Goddard, potato expert from BASF.
Paul explains that dimethomorph in both Percos and Invader 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. Percos (dimethomorph and ametoctradin) has tuber blight control on its label, an acknowledgement to its zoospore activity. Having 2 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.” Paul says 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 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. They are two of the most complete blight fungicides you can get, ticking all the boxes growers are looking for,” says Paul.
“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 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.“
For further information:
Paul Goddard of BASF on 07468 700590
PR contact Jo Palmer on 01760 724469
Photo: Taken by Dr. Ruairdh Bain at SRUC last year