AI steps in to save Scottish potatoes

And it looks like it’s becoming increasingly exclusive – with a mixture of some hellish harvesting seasons, a run of poor prices, and the increasing threats from pests and diseases alongside a shrinking armoury of effective control measures, topped off by sky-rocketing machinery and equipment costs all combining to see a lot of growers quitting the market.

Scotland, with a worldwide reputation for growing high health status seed tatties – due in part to our cooler climate but also to the highly successful inspection and regulation of the sector – has always had a focus on this area, with both the home market and exports to many countries playing an important role.

While a global reputation sees Scottish seed spuds reach many different countries, the debacle which has seen Scottish seed pretty much excluded from sale to EU countries in the wake of the Brexit settlement has probably been partly responsible for the change in the balance of production – with the seed area falling to around 10,000ha while ware production has shifted upwards to around 18,000ha.

That apart, though, the overall farmgate value of production from both seed and ware in Scotland still stands only slightly behind that of what most would consider our main crop, barley – and well in advance of wheat – so despite all its troubles and against a background of falling consumption, you would still have to admit that the sector’s more than just small potatoes.

But the story which The Scottish Farmer broke a week or two back about the compulsory burn-down orders levelled on a number of ware producers due to high level of virus infection has probably added a new chapter to the sector’s troubles – and likely done little to encourage the industry-wide collaboration which is being called for to ensure the industry’s future.

Affected growers – many of whom face not only the loss of their crops but also the heavy additional costs of fulfilling their contracted tonnages from a febrile market fuelled by the lack of free to trade potatoes – have been left facing losses of hundreds of thousands of pounds. And you maybe can’t blame them for feeling that they are paying the price of protecting the reputation of Scotland’s seed sector. Some have suggested that, through no real fault of their own, they have found themselves on the wrong side of what could be a much larger issue.

For despite the country’s reputation for low levels of potato viruses, even the scientists at last week’s event were admitting that the incidence of virus diseases – especially Potato Leaf Roll Virus (PLRV) – in Scottish seed and ware crops appeared to have been increasing over the past five years, a pretty major concern for the future of the industry.

As the disease is spread within and between crops by aphids, climate change has been identified as likely to have played a role in the current situation. Despite the fact that back in the good old days when we had cold winters and could rely on some good hard frosts in Scotland to thin the wee blighters out a bit, the milder winters are more than likely to have contributed to an increased aphid survival rate which would further drive virus spread.

The ban on the use of neonicotinoids back in 2018, which was used to control the aphids, was also likely to have played a part, with the few remaining pesticides already coming under pressure from the insect’s ability to develop immunity to any control measure which is used too frequently.

Crucially for the sector, however, is the fact that infected tubers can harbour and spread the disease from one year to the next, meaning that if the mother crop (of either certified seed or one year farm saved seed) was infected when growing, subsequent crops grown from that seed the following year will also be stricken by the disease – hence the reason why it’s so important to keep the virus out of the crop in the first place.

However, with a continually shrinking armoury of products to halt the spread of aphids between crops, the roguing out of diseased plants from growing crops has played an increasingly important role.

The efficiency of roguing does, however, ultimately depend on the accuracy of identifying symptoms – the development and degree of which are affected by several factors including, it would appear, virus strain and potato cultivar. Indeed, research displayed at Potatoes in Practice showed that variants of the virus exist which cause little or no obvious symptoms to be expressed in the mother crop and scientists have found that leaf roll virus is genetically diverse on a global scale. They’ve also been investigating if and when the dominant strains have changed in Scotland – and how this might alter the symptoms which are exhibited by the plants.

And while many old hands have questioned if modern-day roguers are as good as they used to be, roguing a crop is also undoubtedly an expensive business – costing in the region of £150 a hectare – so no-one wants to spend any more than they have to in order to get through the inspections.

Some agronomists, however, have argued that a change in the main strain of the virus could mean even although plants could be infected with the virus, the lack of normal symptoms at inspection time could be masking both the presence and extent of infection within seed crops. Others have even postulated that regrowth after defoliation could be another possible source of infection which would not be picked up by the normal field checks.

Early results of genetic testing have indicated there has indeed been a change in the dominant strain of PLRV – and that this is now distinct from the ones which were most common only a few years ago. In addition, they are also most closely related to strains first isolated a dozen years ago in Germany which were noted for showing a reduced severity of the main recognisable symptoms, effectively leading to a degree of silent infection.

All of which means that it’s likely to be much more difficult to recognise infected plants – and therefore to control the virus by roguing. On top of this, tests on different varieties of potatoes have found that rather than an across-the-board similarity of symptoms with plants showing the tell-tale discolouration of the leaf edges and leaf rolling, some varieties of potato show virtually none of these symptoms, despite reasonably heavy infection levels.

Models to forecast if and when aphids are around in large numbers and on the move have been developed but researchers at PiP admitted that while the current model has been fairly successful for predicting the pattern and severity of the spread of the Potato Virus Y (PVY) which was formerly the main concern, this hasn’t been the case for the more recent increase in the prevalence of the leaf roll virus. Scientists are investigating other factors, including crop differences, management approaches and classification techniques, to forecast if the disease burden will be greater than in a normal year – and when the threat will be at its most intense.

So far, existing models to forecast the risk of these viruses have not been able to accurately predict the recent patterns with sufficient accuracy, therefore there is a need to develop new models to inform data-driven decision-making.

It is hoped that AI-driven machine learning could be harnessed to develop new national scale warning systems and also to deliver more localised regional warnings.

So, a tough time for tatties –and that’s even before other issues such as the advance of Potato Cyst Nematode (PCN) across some of the prime seed-growing areas and the threat of late blight varieties which are resistant to just about all the main fungicides are added to the ‘one year in 10’ chance of hitting it lucky on the price front which fuels the Las Vegas reputation of growing the humble spud.