Warning of new blight strains for potato growers

Scottish potato growers have been warned to be ready to adjust their blight control programmes in the face of two new strains of the disease which have the potential to overcome normal control measures.

Giving the stark warning to producers at yesterday’s AHDB Strategic Potato open day in Perthshire, crop disease specialist, David Cooke of the Hutton Institute said that the two strains of most concern to the industry were the so-called 36_A2 strain which is highly aggressive and the 37_A2 strain which has reduced sensitivity to fluazinam, one of the most widely used fungicides.

The challenges in managing potato blight – Phytophthora infestans – have always been the main focus of fungicide programmes for potato growers and routine applications to prevent establishment of the disease often take place every seven days.

However Cooke said that while growers were getting used to using the Hutton Criteria forecasts to predict when their crops were most at risk, they should also make sure that they were treating with the right product – and one way to do this was to send samples for DNA testing using the straightforward FTA card system which allows different strains to be identified within a few days.

With the change in weather favouring blight development, Cooke said that although few samples had yet been received from Scottish producers, two thirds of those received from England had been of the aggressive 36-A2 strain – and the resistant 37-A2 strain had been identified as being present in Scotland for the first time last year in a trial crop in Ayrshire:

“With prevention being far favourable to control it is important that growers know that their programmes will be effective – and knowing the strain present in their fields will help them make informed decisions,” said Cooke.

He said that while the normal range of active ingredients could be used to control the 36-A2 strain, knowing that the more aggressive strain was present would allow producers to either use more hard hitting – and hence expensive – treatments or to reduce spray intervals to every five days.

And while there were 13 different actives available for treating potato blight, fluazanim was by far the most widely used and knowing that the insensitive 37-A2 strain was present could allow the use of alternatives which would stop the disease getting a foothold – or becoming silently established and causing huge losses during storage.

The event was the last open day of the Strategic Potato (Spot) initiative with Bruce Farms in Meigle where potato manager, Kerr Howatson outlined his programme for a “golden plot” using the findings from the threeyear project.

These included reduced tillage – with shallower stone separating and no bed tilling – reductions in nitrogen top dressings and soil moisture monitoring – all of which he hoped would add up to a bumper crop at a lower production price:

“Being a Spot farm has helped us to explore many aspects of crop management which are of real interest and benefit to Scottish growers – and has given us the confidence to press ahead with new ideas rather than sticking purely to perceived wisdom,” said Kerr.

• The hunt for a new host is already under way with the AHDB in conversation with seed growers about hosting the next round of the Spot programme.