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SPot Farm West Results Day signposts better PCN management

Publication Date: 
15 March 2018
Author/Contact :
Author/Contact: 
Dr Anne Stone

Practical and applied management strategies for the PCN species, Globodera pallida, were discussed at the AHDB SPot Farm West (Heal Farms) Results Day. Over the season, growers had been able to follow the progression of modified treatments, and the final results were awaited with eager anticipation.

Complementing an application 30kg/ha of the nematicide Nemathorin (fosthiazate) with a mycorrhizal inoculation, resulted  yields topping 40t/ha, ahead of the 32t/ha when the nematicide was used on its own, revealed Anne Stone Knowledge Transfer Manager at AHDB Potatoes.

Dr Stone said: “This is in line with other research showing synergy between mycorrhizal inoculation and organophosphate nematicides.”

However, she cautioned, the work with mycorrhizae was not a scientific trial as it was undertaken in a separate un-replicated demonstration, so it would need further work.

Varietal  tolerance levels, which show the ability to produce tubers despite PCN infestation, were variable, she reported.

There were noticeable differences in tolerance compared with results at the SPot Farm East, Elveden Estate, the variety Arsenal was more tolerant  at Heal Farm than Elveden, whereas Performer, which was tolerant to G. Pallida in the east, was intolerant.

This led to lively discussions from the very knowledgeable audience of growers and agronomists reflecting whether tolerance is in the gene or the root, any influence of determinate and indeterminate varieties and whether the irrigation system makes any difference.

Bill Watts of Harper Adams noted that the ability of the plant to produce and move sufficient quantities of photosynthate (sugar from photosynthesis) around its system despite the PCN invasion to be able to produce a canopy and tuber yield is one of the primary characteristics of a tolerant variety.

“The speed of emergence and root production is also important, and the overall quality of the roots produced are also important. Environmental factors such as soil type play a key role too, building up a complex picture.“

Dr Stone said: “Since tolerance depends on the interaction of varietal characteristics with soil type, irrigation system and weather; categorisation relies on several trials.”

Dr Matthew Back, reader in nematology at Harper Adams, who led the PCN trials and demonstrations, emphasised the importance of the rise of the PCN species G. pallida because of its complexity, which means that while some varieties have been bred to have partial resistance, none so far have been proven to be totally resistant to this pest, although a high level of resistance can be achieved.

Dr Back said: “G. rostochiensis is managed effectively with varietal resistance from the H1 gene, present in a number of popular varieties including Maris Piper. Unfortunately, with  G. pallida there is only partial resistance.”

G. pallida has a longer hatching period and can continue to infect potato roots after the normal working period of a granular nematicide  (3-28 days), he pointed out. Moreover, this species is active in soil with temperatures of just  6 deg. C.

Dr Back said: “As more growers become aware of this threat, we are seeing more calls for better information to help them set up an integrated control strategy.”

The potential of PCN trap crops were also explored on the farm.  These are wild solanaceous species, which have similar root exudates to potatoes and can therefore stimulate PCN. However, once PCN have invaded their roots, the pest is unable to establish feeding sites and consequently development ceases.

Trap crops grown on at Heal Farms included Solanum nigrum (black nightshade), Kenyan Broad-Leaf also known as Garden Huckleberry  (Solanum melanocerasum), Solanum sisymbriifolium, which has been available for use against PCN in the UK for more than a decade, and another Solanum species known as ‘Azo’.

Dr Back said: “Pot based experiments conducted by ADAS showed that Garden Huckleberry could reduce PCN populations by  45-65 per cent, and a separate project in Kenya has demonstrated that African nightshade could reduce PCN by as much as 85 per cent. With a 34 per cent reduction in ADAS experiments, Solanum sisymbriifolium appears to be less effective.”

New SDHI nematicide trialled at SPot Farm

Demonstration plots showed the paces of the first SDHI nematicide, currently known as AR83685 as yields increased from 22.8t/ha (untreated)  to 36/1t/ha (treated). However,  its real benefits come from being used in combination with  one of the current leaders, Vydate or Nemathorin, revealed Gareth Bubb, commercial technical manager at Bayer.

On-label uses will be PCN in potatoes and free living nematodes (FLN) in carrots, but it also has good activity on spraing, said Mr Bubb.  

“It has a low eco-toxicity profile; for example, when it is applied at 625ml/ha there is just 250g of the active ingredient (a.i.).” This means that in the event of reductions in dose recommendations of other nematicides in the future, it could still help growers control PCN levels.

Fully replicated trials are now being done across the country to refine recommendations, some of these will be looking at reducing rates of the other nematicides, such as using a half-rate of Vydate alongside a full rate of AR83685.

The product, which has been approved for a number of countries across the world for some time,  can be applied with whatever set-up the farmer has installed, he added.

Approval is expected for August/September 2018, so a full launch is being planned for the 2019 campaign.

Systems approach to PCN control

Dr Stone  emphasised there is no single strategy for PCN management, and  while rotating varieties partially-resistant to   G. Pallida may help push back against the pest, resistant cultivars should not be relied upon as a management tool in isolation

Dr Back called for  a more ‘systems approach’ to PCN control, with breeders helping growers by specifying the PCN evaluations they have done so there is more precise information on the type of resistance within cultivars, particularly in relation to pathotypes.

“We need broad spectrum resistance, but to get there, research needs to be done on how mitotypes (determined by differences in mitochondrial DNA) relate to the resistance genes within cultivars; a meta-barcoding approach (DNA  high-throughput sequencing) might provide a more rapid characterisation of field populations, so  would be easier to prescribe the right cultivar to grow in a particular location.

Michael Bubb, who  farms around 500 acres of potatoes for processing with his two sons, made two visits to the SPot farm in 2017 and attended the Results Day to follow the development of this year’s trials. He also attended the 2016 SPot Farm West events.

“With the SPot Farm programme, it has been good to see an ongoing progression of learning about an array of topics which are real issues on commercial potato farms,” said Mr Bubb. “I am also able to ask our agronomist more searching questions which come from a deeper understanding of the finer scientific aspects.

“Continuing to be a potato grower means having to make a leap of faith every year to face up to the challenges we encounter.”

He enjoyed the mix of science with practical in-field demonstrations and was particularly interested in  cultural controls for PCN, such as trap cropping, because of the uncertainty around the future availability and efficacy of  chemical controls.

“It is exciting that there is new science out there to help understanding of tolerant and resistant varieties, and biofumigation crops and introduction of fresh active ingredients. Nonetheless, scientists and growers need to work ever closer together to solve the challenges we are setting ourselves.”

He observed that he was pleased to see scientists presenting at the event covered a range of ages and experience, and this demonstrated Harper Adams University to be a centre of excellence on eelworm (PCN)  and associated aspects.  

“These trials and demonstrations show the extent to which AHDB Potatoes is working to enlighten not only the growers but also their customers, about the risks the sector is embracing” he added. 

However, he is surprised that there are not more growers attending these events.

“The concept is good, but for many growers  it can be difficult to get maximum benefit because visits to the in-field plots necessarily take place when everyone is busy with  daily pressures.

“Nevertheless, the practical nature of these events is excellent and the handouts were first-class. AHDB gives honest opinions, going out and meeting the farmers, challenging their way of thinking at the same time that the farmers have the opportunity to have their say.”

Agronomists play a most important role, and making changes based on good science has to be the way forward, he insisted. “As someone else once said, try doing nothing and see what happens.”

Dr Stone said: “The demonstration field proved to be an ideal site  as it has a history of intensive potato cultivation, large numbers of  volunteers, weed seeds which include fat hen and black nightshade, and high levels of PCN type G. pallida.

“This made the land a first-class place to study PCN as part of the SPot West trials.

“It will be interesting to follow the farm through the second year of in-field demonstrations and trials.”

​Further content

SPot West Results Day Presentations

Potato Cyst Nematode (PCN)

 

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