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Sprout suppressant alternatives sought with CIPC use in the balance

As FG went to press in late February, the future of mainstay potato sprout suppressant product CIPC was in the balance. Dominic Kilburn attended an AHDB Storage Roadshow for an update.

Potato store management is facing a challenging future with CIPC use in the balance.

A decision by the EU to confirm the withdrawal of CIPC from the market is expected following its recommendation in 2018 not to re-approve CIPC for future use. In fact, the decision may already have been announced by the time you read this.

However, ahead of the announcement there remains a possibility that CIPC could get a stay of execution.

According to Sutton Bridge Crop Storage Research (SBCSR) senior scientist, Adrian Briddon, speaking at an AHDB Potatoes roadshow event on the Cambridgeshire/Essex border, whatever the decision made by the EU, it is unlikely that CIPC will be available for use by potato store managers for very much longer. “Regulations are changing,” he began. “We’ve had CIPC for 50 years and with the EU recommending its withdrawal last year, there may only be six months to a year’s use remaining.

“If the EU’s decision is not to re-approve it, then there could be a very short use up period, or it could be up to 18 months. We simply don’t know,” he said.

“Gram for gram, CIPC is the best sprout suppressant we have and if it is the case that we lose it, then there will be a number of growers supplying certain markets in the potato industry that are going to struggle,” stressed Mr Briddon.

AHDB is carrying out storage trials to determine how best to control sprouting with the remaining suppressants, should CIPC not be renewed.

“That said, even if CIPC is returned to the market for continued use, it would do so at very different label rates and maximum residue levels (MRLs) to existing,” he pointed out.

CIPC alternatives?

Mr Briddon suggested that other sprout suppressant products that were currently available could play an increasingly important role in potato store management if CIPC use could not be guaranteed for the future, and he highlighted their advantages and disadvantages.

Maleic hydrazide (MH), which is applied to the growing crop as a liquid, typically 3–5 weeks before haulm desiccation, is very effective as a lone treatment, or as a foundation for other treatments. It’s also widely accepted across sectors, said Mr Briddon.

“We see a large proportion of stored crops well controlled with MH although a small number then break dormancy. A lot of MH-treated crops stored long-term have to be followed by another sprout suppressant, and timing then is critical,” he explained.

Application in the field can be restricted depending on temperatures, he pointed out, and last year’s high temperatures and dry conditions made applications very difficult.

“MH got through the recent EU review process but with a restriction which will prevent treated (waste) potatoes being given to stock as feed.

“We hope that this clause will come off the label soon when more work on this is completed by approval holders,” added Mr Briddon.

Other readily available sprout suppressants for growers to consider at the moment are spearmint oil and ethylene (gas), he continued. “Spearmint oil, which doesn’t have an MRL, is currently widely accepted in the fresh sector but not in processing.”

Ethylene has been widely adopted in the fresh sector too and also has no MRL. “Both Spearmint and ethylene are straightforward from a regulatory point of view but their efficacy is more modest and so will likely be used in combination with other products for the most demanding storage scenarios.”

Mr Briddon said that SBCSR is also evaluating DMN (1,4-dimthylnaphthalene) and SmartBlock (3-decen-2-one) as alternative treatments however neither is yet available for use in the UK.

“DMN is Annex 1 listed and availability has been applied for in the UK but not granted as yet. However with the completion of further study work it is hoped regulatory approval in the UK will be soon.

“It is available, and used, in several European countries,” he said. “We want long periods of residual control and these products give it,” added Mr Briddon.

Trials work carried out at AHDB Sutton Bridge Crop Storage Research in 2017–2018 highlighted that, in the absence of MH in a sprout suppressant programme, both spearmint oil and ethylene sometimes struggled to maintain sprout control over a 6–9 month period at 9ºC. Adding MH into the programme, control was generally much better with spearmint oil and ethylene, although for long-term storage sprouting was only well controlled when using long dormant cultivars.

“To get good sprout control in future with fewer sprout suppressants, we need to take into account other factors such as variety dormancy, low temperature tolerance, as well as the use of MH.”

Mr Briddon pointed out that variety dormancy was poorly understood at the moment but it was an area where sprout control could be improved. “Varieties like King Edward and Maris Piper make sprout control difficult, but we are finding more dormant types, like Taurus, are better. In addition, use of low temperature tolerant varieties (where crop can be stored at lower temperature without damaging fry colour) helps by extending dormancy and reducing the overall sprouting pressure. These will be much more important factors in the future.

“Work is on-going but we will be able to provide more information on established and the latest varieties in terms of their likelihood to sprout more or less than others,” he added.

Application kit

Mr Briddon also suggested that, as other sprout suppressant products became more widely used by store managers, then application equipment would also have to change. “Petrol-driven hot fogging applicators are the key kit for UK sprout suppressant application in stores, however as a by-product of combustion when applying CIPC, ethylene and carbon dioxide are produced which can affect potato fry colour.

“As a consequence stores are normally flushed through with air a few hours after application of CIPC to prevent this, but vapour phase products such as spearmint have to remain within a sealed store for at least 24 hours following application to maintain efficacy.

“Electric-driven or alternatively-powered machines will have to be considered instead of petrol-driven and this will affect contractors in the industry and the time it takes to apply a sprout suppressant to a stored crop,” he said.

Mr Briddon concluded by saying that SBCSR is also gathering data on the residue level of CIPC on potatoes in stores which haven’t had an application of CIPC for one or two years. “If approval for CIPC is not renewed then the MRL for CIPC will revert to 0.01ppm. Our work suggests that contamination from CIPC residue remaining in the store fabric could result in an exceedance of this level.

“Therefore the aim of the work is to provide information that could allow a temporary MRL to be set that wouldn’t interfere with marketing of potatoes in the future.”

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