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Sprout Suppression 2020

23 April 2015

Effective sprout suppression is fundamental to managing stored potato quality.  In April over 65 potato industry movers and shakers including regulators and approval holders, gathered in York for AHDB Potatoes Sprout Suppression 2020 forum to debate the future.

For more than fifty years Great Britain has been heavily reliant on chlorpropham (CIPC), as a cost effective and efficient potato storage treatment.
It is still used in over 90 per cent of all post-harvest sprout suppressant applications, but there has been a recent increase in the availability of alternatives to spread the risk and to find treatments that can replace or complement the stalwart product.  Delegates at Sprout Suppression 2020 passionately debated the way forward with the aim of defining and steering best practice for the use of sprout suppressants over the next 5 years.
The regulatory landscape 
CIPC stewardship has reached a very high standard, evolving from the Potato Industry CIPC Stewardship Group into ‘Be CIPC Compliant’ (
The current position with CIPC has been well publicised.  “Today there’s real danger of severe constraints or CIPC withdrawal if every member of the industry doesn’t follow stewardship guidelines and Be CIPC Compliant,” stated AHDB Potatoes head of R&D, Mike Storey.  “It’s serious.  A further MRL exceedance could trigger CIPC’s withdrawal from use.”
“A reality we have to face is that in the future we will have fewer pesticides available,” noted legislation expert Ian Finlayson of Practical Solutions International (pictured right).  “CIPC comes up for renewal of its registration in 2017 and the data package is already submitted.”
The industry is making good inroads.  “Total usage of CIPC is down by 51 per cent compared with surveys carried out in 2002 and 2006,” said Adrian Cunnington, head of Sutton Bridge Crop Storage Research (SBCSR).  “However, as an industry we have to go further.”
“This season’s market situation makes reinvestment a challenge.  But many of our growers may have to accept that their stores are no longer compliant with CIPC best practice, which ultimately may mean having to invest in modifications to improve airflow and, in some cases, positive ventilation.”
Pace of change
“Our potato industry is centred around an annual crop.  It means you can only make one change each year,” said Steve Billings, chairman of the Potato Processors’ Association (PPA) technical committee.  “So, if you want to try something new in field or store, you have to make a small change and then monitor the impact for the whole season.
“You might need to hold this small change for a number of seasons until you feel you have covered all variations that the seasons can throw at you.“
Sharing findings from overseas is one way of gaining knowledge faster.
A view from the US
Idaho grows 120,000 hectares of potatoes, a similar area to Great Britain.  The lion’s share of the plantings is for the processing sector, but fresh ware and seed is also grown.
Potato storage expert Professor Nora Olsen, from the University of Idaho (pictured right) gave a unique insight from the States, where the US CIPC Maximum Residue Level (MRL) is set at 30mg/kg ppm, a level three times higher than afforded in the UK.
“We consider ourselves as almost a sister research facility to Sutton Bridge Crop Storage Research and we’re constantly sharing information,” noted Professor Olsen.  “This is especially important for new products we have regulated and have experience of, that will soon become available in the UK.”
“We applaud the ‘Be CIPC Compliant’ campaign; CIPC stewardship is an absolute global priority.”
The typical Idaho store holds 7,000 tonnes in bulk at 6 metres deep.  Therefore the stakes are high, which makes management, airflow and sprout suppression distribution in store front of mind — just as it should be in the UK.
The major sprout control options available in the US:
  • Chlorpropham (CIPC)
  • Maleic hydrazide (MH) – Field applied and also aids volunteer control and crop uniformity
  • Mint or other essential oils
  • Clove oil (Biox C; Sprout Torch) – Not suitable for UK market
  • Diisopropylnaphthalene (DIPN; Amplify™)
The major US sprout control options soon to be available in the UK market, which can be used in an integrated programme with CIPC:
Dimethylnaphthalene (DMN; 1-4Sight™) – Registration expected in the UK in 2015.
DMN is effective in both pre-pack and processing stores.  It is a reversible sprout suppressant and can be used to control growth in seed crops (1,4 SEED™).  Seed treatments are reported to result in changes to progeny tuber size distributions.
It is a volatile, oily liquid and is likely to be applied by contractor as a hot-fog.  In Europe, it is a DormFresh product that will be marketed by BASF.
3-decen-2-one (SmartBlock™) – Registration expected in the UK in 2016.
3-decen-2-one was identified in research at Washington State University and is being commercialised by Amvac.  It was already approved as a food additive and received US registration as a sprout suppressant (SmartBlock™) in February 2013.  It is exempted from an MRL (Maximum Residue Level) in the USA.  It is a volatile, oily liquid and is likely to be applied by contractor as a hot-fog.  It will be marketed in the Europe by Certis.
Alternatives currently available in the UK
Ethylene has been available for a few years under a commodity approval, and companies Restrain and BioFresh currently supply equipment for ethylene control.  Ethylene is a gas, so losses from store can be relatively high and equipment has to be installed to introduce or generate the gas in store.  Sprout control is completely effective in low-temperature stores, with a head-space concentration maintained at around 10ppm.  There is little residual effect and sprout control is lost soon after removal from store.
Its application in processing storage is subject to on-going research at SBCSR, primarily to overcome any unwanted effect on fry colour.  Sprout control by ethylene is reversible and it is used as a commercial seed treatment for increasing stem numbers in susceptible varieties.
Spearmint oil (active substance R-carvone) received full UK registration (Biox-M, MAPP 16021) in 2012.  Its use is increasing in pre-pack stores but, in processing stores, is likely to be cost-prohibitive except for niche markets.
As well as being an effective sprout suppressant, spearmint oil can rapidly burn back existing sprouts.  It is a volatile, oily liquid which is applied by a contractor as a hot-fog, using a proprietary electric fogger.  Sprout control is reversible, with growth resuming when residue levels decline below a critical threshold.
Getting the best from new options
“New products require a different store management approach and a specific understanding of their application,” said Adrian Briddon from SBCSR.  ”CIPC is a solid with long-lived residues.  However, the new generation of sprout suppressants tend to be either gases or volatile liquids, which gives far more flexibility in building use.
“In stores where CIPC has been previously used, this restricts subsequent use for seed tubers and all other crops.  The volatile liquids in the new generation of sprout suppressants will dissipate from store fabrics relatively quickly.  Therefore allowing more flexibility and alternative uses of the building after the stored crop has been used.”
Sprout suppression by the new products tends to be reversible, with growth resuming as residue levels drop off.
Because of a loss of apical dominance, some treatments may have a modifying effect on stem numbers and are being used successfully in seed management.  Some of the essential oils available are also reported to control some pathogens.
Many of the new sprout suppressants need longer store closure periods after application to ensure complete ‘uptake’ of products from the vapour phase.  In many cases, store closure for 24 hours is likely to be a minimum label requirement, so for processing storage, different equipment and application strategies are likely to be needed.
Customers and the cool chain
Professor Olsen demonstrated the need for sprout control post-storage.  In Idaho, potatoes can take up to 20 days to reach their market by rail and then spend a further 7 days being distributed to retail stores.
Great Britain has one of the shortest cool chains in the world.  But sprout control is still important when fresh potatoes are transported, at point of sale and ultimately in the hands of the consumer.  
“Storage is a critical component of the potato production process,” noted Mr Billings.  “Some crops spend longer in store than they do in the ground.”
“A tuber is very much living and respiring and reacts to store conditions.  It follows therefore, that potatoes in stores should be afforded a similar level of management input as might be applied to a growing crop.”
Storage type 
The meeting heard that there has been considerable progress in best practice for CIPC applications in stores.  “Particularly in bulk storage, this has enabled us to move a long way forward to improve efficacy and the evenness of application, and to significantly reduce our total applications of CIPC” said Dr Storey.
“Box storage is more challenging because there is far greater variation in store design, box layout and the design of the boxes themselves.  Box storage is more common in the fresh supply chain, but with a number of fresh growers switching to supply the processing sector, this is a cross-industry issue.”
The challenge 
The forum concluded by collating the views of the delegates during the afternoon workshops, to feed into decision-making which will dictate the shape of sprout suppressant research, development and stewardship.
“Is the efficacy of the new chemicals as good as CIPC?,” questioned Mr Billings. “PPA members are taking part in different research projects investigating alternatives, so the industry is open to the potential of other suppressants.
“There is however a need to research new protocols to get the best from them, and, in our ever challenging environment, how do we adopt these new chemical options without adding cost to our supply chain and ultimately our products?” he challenged.
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