As featured in Arable Farming Magazine
Seeking new ways to protect potatoes
by Arable Farming Feb 2021 Issue
The loss of a number of key actives from potato growers’ armoury has seen on-farm innovators looking at new ways to tackle pests and diseases. Alice Dyer takes a look at some of the latest developments.
Diquat and pencycuron are among the key actives the potato sector has had to wave goodbye to in the last year and now the future of mancozeb also hangs in the balance.
Following an EU decision against reapproval last autumn, the fungicide has gained a temporary reprieve here as a result of post-Brexit legislation, which rules that active substances due to expire in the EU within three years of December 31, 2020, will be granted a three-year extension under the new GB regime.
Mancozeb’s multisite activity has been essential in ensuring growers are able to implement a robust spray programme containing alternating modes of action and without it building a cost-effective disease control programme is going to be a problem many growers face going forward, believes seed potato grower Tom Cargill, who farms in north east Scotland.
Mr Cargill’s farm, which sits between Aberdeen and Dundee, exports around 70% of its seed potatoes to countries outside the EU, including Iraq, Egypt and Thailand.
And while alternaria, which is controlled by mancozeb, is not much of a problem in Scotland, some varieties suited to export are susceptible, he told the BCPC Disease Review.
“We grow Atlantic, which is susceptible [to alternaria], for the Thai market, so it will be interesting to see if we can still grow it without mancozeb.
Burndown periods
As well as facing challenges with aggressive blight strains and access to only two aphicides to protect potatoes against virus, burndown periods are also causing problems with the crop’s marketability.
“Countries we are exporting to generally want the product earlier and earlier, so rapid burndown is important.
The products available now are not as effective in comparison to diquat, so we’re using a flail and then using a PPO inhibitor like Spotlight, which requires sunlight.
During August we can get very dull days which reduces the [product’s] efficacy and the crop stays greener for longer, which means more problems with aphids and virus.
The flail is also problematic in a wet season and [delays getting on the field mean] potatoes get bigger and become unmarketable.” At the end of December 2020, the Emergency Authorisation (EA) for nematicide, Vydate (oxamyl) which has been rolled over on an annual basis in recent years, expired and has not been renewed.
As things stand, growers will have until February 28, 2021, to store and dispose of stocks unless the new EA applications submitted by AHDB are approved.
Vydate has been an important tool for growers of potatoes, sugar beet, onions, carrots and other field vegetables to control pests, including potato cyst nematode (PCN), but some are now exploring alternative approaches – including cultural control.
Ten years ago, Wantisden Hall Farm, Suffolk, was experiencing very high PCN counts, but since introducing pigs to the rotation, the pest population has fallen to virtually nothing.
Around 55 hectares of the farm, which grows potatoes, sugar beet, veg and cereals, are now let out to a local pig producer.
Speaking during a Cereals Live Q&A webinar, farm manager Tim Pratt said the biggest benefit associated with the pigs was clearing up volunteer potatoes.
“PCN is probably one of the biggest problems in potatoes and there are resistant varieties out there, but realistically we need to get them to market.
“We had some quite high [PCN] levels and going for the second year with pigs in the field, we could basically reduce PCN levels to nothing.
Structure
“It works very well for us. Working behind farrowing fields is nice. They are quite level and haven’t made a mess of the field.
Dry sow fields have high [stock] volumes so can make a bit of a mess.
We try to move dry sucklers every year to limit damage done to the field.
“[In 2020] we had a wet autumn like a lot of people and they do make a bit of a mess, but a couple of days after all the pig huts and fences have gone we can level it off, subsoil and get a bit of structure back and create a decent crop after it.” As well as clearing up groundkeepers, there are also fertility benefits, Mr Pratt added, with soil P and K levels typically increasing by an index of 1 after pigs.
“We’re getting paid to put nutrients back in the soil, but site selection is very important.
You’ve got to have nice light, level and sheltered land.” There are some issues with pigs, he added, including erosion and fertility hotspots.
“We also have to be careful what we follow in the next crop.
We usually follow with maize and sugar beet because they’re good scavengers of fertility and we spent quite a lot of time levelling hotspots off where the huts had been.
“We’ve got to a position where we don’t see those hotspots now,” said Mr Pratt.
Tackling virus with natural predators
With a reputation for excellent plant health underpinning markets for Scottish seed potatoes, growers are looking for new ways to combat aphids amid falling insecticide efficacy and availability.
Trials are being carried out to assess the effectiveness of growing flower strips in tramlines and headlands to promote natural predator populations and reduce aphid-transmitted viruses in potatoes.
Eric Anderson, senior agronomist and potato specialist at Scottish Agronomy, is leading the trials with grower and AHDB Strategic Potato farm host Jim Reid, of Milton of Mathers Farm, who produces 80 hectares of seed potatoes.
The virus incidence in 2019 seed potatoes crops hit a 20-year high and 2020 inspections gave a similar impression.
Mr Anderson says: “The main culprit is Potyvirus, PVY, principally the PVYN strain, but PLRV has also increased, albeit from a very low base.
PVYN is causing the greatest concern.” Low growing plants During the trial, Mr Anderson identified low growing plants which measure the same height as potato crops, including cornflower, common vetch and yarrow, as highly effective in attracting natural enemies of aphids.
At Milton of Mathers Farm, three-metre wide strips of this mix were drilled between the tramlines, creating floral food resources and a refuge habitat attractive to hoverflies, lacewings and ladybirds.
Mr Anderson says: “This created corridors closer to the crop, increasing biodiversity in a move away from a monoculture system with its high reliance of chemical controls and creating greater impact as the predators are closer to the pests.
We are still refining, to assess whether the species sown and sowing dates have an impact on the value of the strips and whether they support the types of natural enemies needed to control potato pests and to deliver them to the crop when needed.”
Challenges
However, one of the challenges of relying on biocontrols is the lag period because natural enemies take time to build their numbers, Mr Anderson adds.
“It has long been recognised that aphids are preferentially attracted to light reflected from soil in blank beds and the contrasting neighbouring plants.
Sowing wildflower mixes or alternatively spreading straw mulch in these blank beds are practical mitigation techniques for early generation – FG2 and FG3 – seed growers, with a disproportionately higher number of separation zones between the numerous seed stocks.” The effectiveness of the strips in boosting pest control strongly depends on their botanical composition.
“Often non-crop elements that are designed for bird or pollinator conservation do not simultaneously make resources available to biological control agents,” Mr Anderson says.
Similar research in Switzerland is said to have shown that of the three natural aphid enemies, hoverflies increased the most in the strips compared to surrounding potatoes, while the populations of lacewings and ladybirds also rose significantly
Biological solution to late blight on the horizon
A biopesticide derived from the broad-leaved weed common mugwort is being developed after a grower saw markedly lower disease and pest instances in crops where the weed was present.
Yorkshire veg grower M.H. Poskitt has teamed up with sustainable crop protection product developers Eden Research to create and trial the new biofungicide product designed to protect and improve the quality of root vegetables.
It is hoped the project could eventually provide farmers with a naturally-based, chemical-free product to protect against late blight in potatoes.
Sean Smith, chief executive officer at Eden Research, says: “It’s actually not that unique a situation.
Poskitt’s farm manager James Bramley had been walking field boundaries and happened to notice in an area a fairly common weed was present, crops looked more vigorous and generally healthier with lower incidence of disease.
He noticed this across a couple of crop groups including potatoes, carrots and parsnips.” Poskitt’s growers and agronomists then undertook their own experiments, turning the weed, common mugwort, into tea and applying it to plants, where the impact was quite clear, Mr Smith adds.
Conclusive
“On late blight they saw some pretty conclusive results, much stronger than what they would have anticipated, so they started speaking to regulatory consultants to find out about product development.” Over the next two years, Poskitt and Eden Research will develop and commercialise the product.
“We think it’s a class of compounds broadly referred to Biological solution to late blight on the horizon as terpenes that is having such good activity against late blight.
We are now working to create a product that is efficient and gives consistent results.” And while some might consider bioproducts a compromise in comparison with chemical controls, Mr Smith says they have the potential to replace less sustainable inputs, with some products already showing better efficacy than their chemical comparators.
“We have always had this view that we need to go out there with efficacy that is comparable to conventional chemistry.
“IPM is the future and the way we see Eden fitting into this is replacing the chemical component of an IPM programme where possible.
For example, when we are looking to prevent or cure botrytis on grapes, we have products that perform at least as well as active ingredients so we’re going head-to-head with chemical products.
