Two years ago sweet potatoes were added to the inflation ‘basket’ operated by the Office of National Statistics. The reasoning? They had become ‘popular in the nation’s kitchens’. They were accompanied into the basket by protein powder and e-cigarettes, ousting yoghurt drinks and sat navs. SALLY SMITH reports
The onward march of the sweet potato continues, and with each one that is eaten another ‘real’ potato is likely to lose ground. So will other staples, of course; there’s a limit to the quantity of starch which can accompany any meal, but the preferred alternative to regular potatoes does appear to be the sweet option.
In this there is ‘healthy’ backup – despite the current campaign to reduce sugars. The Food Standards Agency includes them as one of the five, (now ten), a day as it classes them as a ‘vegetable’. Alas, potatoes are not accorded the same sacred status. Numerous weight reducing plans advocate their inclusion though calorifically they are very far from being ‘slimming’, containing, as they do, such quantities of the latest horror, sugar.
Thus the perception has grown that not only are sweet potatoes the healthy alternative but the slimming one too. In an informal Potato Review survey of people ranging from pensioners to teenagers, over and again the fact that they were ‘less fattening and more healthy’ was produced as reasoning for consumption; one fashion-conscious young woman even stated that she ‘never ate regular potatoes at all now’.
Kantor Worldpanel – the consumer research organisation – has figures for consumers switching from regular to sweet potatoes to the year ending May 2016 (the latest annual estimate will be published later this month) which show a net 34% growth in the switch with volume rising to 30,000 tonnes. This contrasts with a further reduction in consumption of regular potatoes.
Explains Jimmy Phillips, senior marcoms manager for AHDB Potatoes: ‘Sweet potatoes are seen as a healthy alternative when consumers fancy something different or look for variety in their diet.’ He cited the Kantor survey in which the highest proportion/number put health benefits way out in front of the other reasons for the choice which include: to get a portion of vegetable (this one running a close second); to provide a varied diet; more natural/less processed and lower in fat/salt/sugar.
With their overwhelmingly sweet taste, it seems inexplicable that anyone should conclude these tubers are all these things, but they do. In our – admittedly unscientific – survey, enthusiasm did follow age, decreasing as the years of those questioned rose.
Cover crops: the benefits and the pitfalls
Cover crops are often promoted as a panacea, improving soil conditions and building fertility to help in the battle to keep inputs to a minimum without compromising quality or yield. This leads to high expectations from farmers who may then be disappointed when they try them out. Heather Briggs considers the potential advantages as well as advice on when not to use them.
Growing cover crops can be a complex operation and may create potential problems if strategies are not well thought through, warns Eric Anderson of Scottish Agronomy. He suggests, for example, that green bridge transfer can occur which could lead to an increase in pests and diseases.
‘In potatoes, having a cover crop planted over the preceding winter has the potential to provide a green bridge for the peach potato aphid (Myzus persicae) which could then infect crops of seed with virus and processing potatoes with aphids,’ he says, adding that if the insects survive the winter in a cover crop they are then well placed to move through to the canopy of newly emerging plants – including cereals and vegetables, in addition to potatoes.
The most important viruses transmitted by aphids to potatoes include potato leaf roll virus (PLRV), potato virus Y (PVYO and PVYN (veinal necrosis)) and potato virus A (PVA). In the field, a low PVYn incidence does not always results in yield reduction because the poor growth of infected plants can be compensated for by neighbouring healthy plants but, typically, secondary infection rates of 15% can turn into yield losses of between 2.5% and 16%, depending on the variety.
High populations of aphids can cause direct feeding damage to potato plants, giving rise to false leaf roll where insect numbers increase rapidly on the upper parts of the plant of varieties such as Desirée. They can also raise reducing sugar levels, thereby adversely affecting fry colours in processing crops.
Growers looking for biofumigant properties to help reduce levels of pests such as PCN also need to think again if brassicas (particularly oilseed rape or veg brassica) are grown in the same rotation, as growing mustards may result in an increase in club root, warns Mr Anderson.
For many growers, one of the main reasons for introducing cover crops – sometimes known as green manures – is to help build soil organic matter (OM). Applying farmyard manures, chopping straw or adding grass leys into the rotation all contribute although this is a very slow process. Moreover, the benefits may not be directly proportional to the OM content.
Mr Anderson explains: ‘Soil organic matter is made up of both living and non-living components, including carbon and carbohydrates. Carbon, of course, is inert but adding soil amendments containing carbohydrates to the land affects soil properties, biological turnover and functionality. There is a growing body of evidence that the “active” fraction of OM is more important to soil properties than the total. This fraction consists mainly of recent additions from crop residues and organic manures.’
DuPont strikes gold with Zorvec
Anyone who has visited John Keer’s annual blight fungicide trials near Holbeach in Lincolnshire over the past four years or so will have seen plots treated with a novel ‘wonder’ product. David Mossman has been talking to the manufacturer ahead of a launch planned for next year
DuPont has been very quiet during the development and introduction of the chemistry behind its latest blight fungicide but now there are plans for a UK launch in 2018, subject to regulatory approval. Ahead of this there will be a limited release of the new fungicide and its partner product for demonstration trials in Britain and Ireland this summer. The active substance, oxathiapiprolin, forms the basis for a family of fungicide formulations which are already sold in a number of countries globally under the trademark Zorvec. The active substance was granted European Commission approval in March this year, paving the way for a UK authorisation in 2018.
According to DuPont, Zorvec offers ‘an unmatched combination of consistency and long-lasting control of downy mildew and late blight, even under challenging environmental conditions’. On potato crops it is said to give three to four days of additional protection when compared with current market leading fungicides. ‘This is one of the most exciting products we have developed in decades,’ said fungicide technical director Bernard Straebler.
UK Country Manager Robert Bird explained why Zorvec had raised so much enthusiasm among DuPont development chemists and sales staff alike.
‘In a market which looks at blight products in terms of seven-day intervals this one is a very solid ten day treatment, being much more robust than current standards. Potato growers face a wide range of challenges, many of which differ from other farmers; they will have potatoes in the shed from last year, a crop going into the ground now and they are already looking for land for next season.
‘The big factors which affect potato production, such as the weather, they can do nothing about. We asked a group of growers what they would want from a new blight fungicide and number one on the list was longer spray intervals. They would still like a systemic product, but they also want fewer applications, fewer hours spraying and a reduction in crop damage as they go through the field less often with the sprayer.
‘When you start speaking to the packers and processors there are other considerations that come out, such as showing a reduction in carbon footprint to meet market protocols and using less active ingredient per hectare – there is a perception that they need to reduce the loading on the potato crop.
‘When we quantify what farmers want from a new product, persistence is high on the list but then they also want curative activity. The seven-day programme is a relatively new development driven by the late blight pathogen and available chemistry. The reality is that growers will happily work with longer intervals. Give them up to an extra two days free from spraying for blight and they see a cost saving on machinery and they gain time to do something else on the farm. Reducing the number of blight treatments and the total amount of chemical applied is very much front of mind for potato growers.’
DuPont points out that Zorvec is active at the very low rates and has an excellent toxicological profile. The label recommendation is likely to be for up to four applications per season.