Survey reveals threat from potato soil pest problems
Potato Cyst Nematode (PCN) remains by far the most serious pest that is challenging profitable and sustainable potato cropping across the UK. The most serious soil pest now questions the viability of potato production on 17% of UK potato farms, although 69% say they have the populations in check or getting better.
In the wide-reaching potato soil pest survey of growers and agronomists, responsible for around 20% of the GB potato area, PCN was deemed the most serious soil pest problem on 65% of farms, with 14% of respondents stating Free Living Nematode (FLN) is the most serious and wireworm the biggest problem for 20% of growers.
The Syngenta Soil Pest Survey revealed 81% of respondents reported PCN issues on their farms – with 17% of the total saying it was a problem across all their farm and 64% on part of the area; for those with only partially affected farms the average area of PCN infected land was 35% of the land.
The on-line survey involved 70 growers and agronomists, covering over 20,000 hectares of potato cropping, with an average area of 290 ha. Responses were received from every region of the country, with a bias of 45% from the east of England and included 15% from the south west and 16% from Scotland.
Commenting on the survey results, Syngenta Potato Technical Manager, Douglas Dyas, said: “This is the first time the survey has looked at the complex interaction of all key soil pests and the matrix of agronomy options for their control. It also addressed growers’ opinions on the effects on profitability and long-term viability of the business.”
Given the long-term implications of soil pests, the survey also asked about the changes seen over the past 15 years. For PCN, only 3% of respondents have said problems were getting worse and out of control, although for 27% whilst it is still getting worse, they do now feel they have the tools and knowledge to get it back in control.
The biggest group, 30 of the 70 growers, had seen no significant change in PCN populations, with 17 believing that it’s getting better and they have a handle on control. Just one grower reported a significant improvement in the situation.
“Growers and agronomists are clearly adopting a variety of Integrated Crop Management techniques to evaluate what works best on their farms and how they can be utilised alongside nematicides to manage risk and pest populations,” commented Douglas Dyas.
“It is apparent that all of the techniques have some merit. However, there is no one single option that stands out as being universally successful. For most, it has just been holding where they are,” he added, “but there are encouraging signs that if all the options can be used, growers believe they can make steps to improve the situation.”
In terms of agronomic techniques to manage PCN, the most effective options were, unsurprisingly, still seen as seeking out clean land, or taking worst affected fields out of the rotation. However, growers clearly recognised that availability of clean land is an issue – with nearly 25% unable to use the option.
Extending the rotation was the most widely used option, adopted by 95% of the respondents. Of these, 17% reported the results had been extremely effective and 45% good results. Everyone had seen some effect from using the technique, although for 8% it had been variable.
Nearly 50 of the 70 respondents had tried PCN resistant and tolerant varieties. Growing resistant varieties had proven more successful, with half of resistant variety growers seeing good or extremely effective results for managing PCN populations. However, only a third were achieving such success with tolerant varieties to protect yields. Some 16% had seen variable results with both options.
The move to treating fields at lower PCN counts with nematicide to prevent populations from building up had been practised by over 80% of growers and agronomists, with 81% of them reporting positive effects – 7% of which were extremely effective. A move to a more effective nematicide had seen a 30% good or extremely effective result.
Half the respondents had utilised bio-fumigants, and a similar number trap crops as further PCN management tools. Results with bio-fumigants appeared more successful than trap crops, with four respondents finding bio-fumigants extremely effective and two-thirds stating some or good effects. Half of grower who had used trap crops had seen some effects, but a quarter reported no effect. Variable results with these techniques were reported by 9% who used trap cropping and 11% with bio-fumigants.
Syngenta Soil Pest Survey 2017 – Growers’ comments on PCN control strategies:
“A combination of cultural, bio-controls and pesticides appear to be slowly bringing populations down.”
“The distribution (of PCN) is widening. There are control options available and that work (particularly variety choice) however, once the pest is present I have not experienced its elimination.”
“Resistant varieties, longer rotations, strategic cover crops and better utilisation of Nemathorin through improved application all help. Keeping on top of things like groundsel help the battle with FLN too.”
“Six year rotation between potato crops; using bio-fumigation methods as and when required; acquisition of clean certified seed; regular equipment wash downs.”
“Bio-fumigants, extended rotation and nematicides all help minimise damage.”
“Now grow potatoes one year in 7/8 - it has increased yields and improved quality.”
“Sisymbriifolium crops (Nightshade trap cropping) work better out of a potato rotation. Caliente mustards work well but timing is crucial. Improving soil bacterial and fungi biodiversity helps bio-controls to be more effective.”
Growers who had their soil samples speciated for PCN type (44% of the respondents), reported 100% now included G. palida, with 66% showing mixed populations that included G rostochiensis. “That is a significant shift over previous assessments,” pointed out Douglas.
“It highlights the challenge facing growers from the more aggressive PCN species. The prolonged hatching of pallida cysts over the season can cause greater crop damage and, if a shorter duration nematicide has been used or application inconsistent, result in greater build-up of populations at the end of the season," he advised.
“There are fewer varietal options for resistance or tolerance with pallida, and its cysts also remain viable in the soil for significantly longer, compared to rostochiensis; growers will need to leave longer rotational gaps between crops for any significant natural decline.”
The survey revealed that still relatively few growers and agronomists - less than 5% - are taking both pre- and post-crop soil samples from fields, to assess the effectiveness of PCN control programmes. Of those who undertook pf:pi testing, the typical aim was to at least hold populations, and preferably see a 10 to 20% decline in populations through the crop season.
Growers’ comments did throw up that using bio-controls appeared to have highly variable pf:pi results, with population reduction ranging from 75% to no effect year-on-year.
“In terms of the implications of PCN on business profitability, around one in five of survey respondents said the pest was making the viability of continued growth questionable, with a quarter saying the effect was very serious ,” pointed out Douglas Dyas (above). “Less than 10% of respondents said PCN had no effect on the business profitability, which has highlighted the importance of tackling this key area of concern.”
With FLN, over half the growers and agronomists reported the pest was a problem on some fields, with 10% seeing issues across the farm. Some 38% reported FLN caused no concern for their potato cropping. Of those with some problem FLN fields, it averaged a quarter of their available potato land, however, as noted by one grower: “We’re not sure really as we only occasionally test for FLN, but this is an area we should look to develop.”
The financial implications of FLN on business profitability were also seen as far less serious for most. A third reported no effect, with some effect seen by over 30%; however, FLN has had a very serious effect or question the viability of future potato growing for fewer than 10 growers out of the 70 respondents.
“Of the effects FLN causes, spraing was seen as having a very serious effect by 21% of respondents and, for three respondents, serious enough to question the viability of continued growing,” said Douglas. “Other effects seen by growers and agronomists highlighted significant or very serious effects for inconsistent tuber size reported by 37% of respondents and 35% for inconsistent tuber maturity.
“Other issues were pinpointed around slow emergence and damage to rooting. Over 40% reported some physical tuber skin damage, but as a significantly lower issue compared to other effects of FLN,” he added.
The vast majority of survey respondents (72%) reported no significant change in FLN populations over the past 10 years. However, for nearly 10% they saw the issue as getting worse and out of control, whilst a further 10% were also seeing it getting worse – but with the belief that they had the tools and knowledge to redress the problem.
“When asked specifically about spraing incidence in the 2016 season, when many growers switched to Nemathorin because of lack of Vydate availability, the survey revealed better results for 26% of those it applied seeing significantly less incidence than normal," reported Douglas.
"A further 21% seeing less than normal signs of infection,” he commented. "It was an average season for around half of growers and agronomists, with only six respondents reporting more spraing than normal."
Growers’ feedback on management options for FLN highlighted the need for longer rotations and the search for spraing resistant varieties that could be strategically used in the rotation on known affected fields. The potential for break crops and the importance of weed control, such as groundsel, to reduce populations was pointed out, however that was being hampered by overwinter stubble regulations.
Wireworm was reported as a problem on just over half of farms, but more typically as a sporadic pest - with an average 22% of fields on affected farms showing problems.
“When it comes to the overall costs of soil pests on farm profitability, the implication of lost yields is seen as the biggest factor that threatens the viability of potato production,” said Douglas. “11 of the 70 respondents cited that as the highest ranked risk.”
“The survey showed that the cost of nematicide is a major concern for growers, which makes it all the more important to get the best possible performance from every application,” he added, “particularly where reduced tuber quality is seen as a very serious effect or making viability questionable for nearly a third of growers.
"There are clear indications that growers and agronomists believe soil pests, particularly PCN, can be managed with the full portfolio of control options available, but they are still a major hurdle to many potato businesses to remain profitable in the future.”
“The results of this survey will further help to focus the industry on key areas of soil pest issues and control that need to be redressed," he added.