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Going Dutch: Potato store managers in Britain will need to split the sprout suppression load next year

Store managers may need to consider beyond the direct costs of the remaining approved sprout suppressants and towards adjusting store management strategies to keep the number of applications to a minimum,  and therefore helping to keep costs down, according to a recent news release issued by AHDB in the UK.

As sprout suppressant chlorpropham (CIPC) will not have its licence renewed in the EU, the hunt is on for cost-effective alternatives, AHDB says.

Spearmint, marketed as Biox-M, and dimethyl naphthalene (DMN, marketed as 1,4 SIGHT) are both approved for use in the Netherlands, but both are more expensive.

Spearmint oil is one of the recent additions to the sprout suppression tool box, having received full UK registration in 2012. The active ingredient is the naturally-occurring substance R-carvone, a terpenoid, and is applied as a hot fog to burn back existing sprouts. DMN, is approved for use in the Netherlands and is likely to be submitted to the UK’s Chemical Regulations Directorate (CRD) for approval later this year.

Dutch perspective

However, while it can deliver robust sprout control, costs of using it can be as much as seven times higher than CIPC in application costs for each treatment, warns Jeroen van Kappel of Netherlands-based Mooij Agro, who has been trialling both spearmint and DMN across multiple sites. 

Moreover, as spearmint oil is relatively volatile,  stores need to be closed for 48-72 hours after application as otherwise it could be lost as a vapour, resulting in lower efficacy.  

Application is recommended with an electrical fogger, although other approved equipment may also be used. Circulation fan speed needs to be at 100 per cent for best results, the ongoing trials have found.

Jeroen says: “When it is applied stores have to be closed for 48 hours or more, ideally with no natural ventilation.

During fogging, the supplier recommends running fans on forced internal ventilation. Because of the closure it is not possible to avoid the crop temperature rising as it is important not to  run refrigeration units during the period of store closure.

Fry colour and CO2 

“The problem with closing stores is that levels of carbon dioxide (CO2) can rise significantly. If this is for a short time, it seems like the fry colour remains acceptable, but if closure is for too long , it could become be an issue.”

Further research will be undertaken on the effects of the rise in CO2, and from 2020 the trial stores will have a new CO2 sensor capable of measuring 0-10.000 PPM. The effects of longer closure on weight loss and fry colour are also being explored.

 “So far, fry colour has been acceptable, although only the one variety, Fontane, has been used in our trials to date. The decision to just use one variety was taken to keep the number of variables down and ensure comparable data,” explains Jeroen, adding that the fry quality work has been cross-referenced by specialists Lamb Weston.

Weight losses measured in February were around 2.1 per cent,  and in June, they varied between 4.2 and 6.2 per cent; this variation may have been due to one of the farmers using only cooling, whereas the others used both cooling and outside air.

DMN is also applied as a fog, and the temperature  of the tubers needs to be above 5 deg.C. For best results, fan speed needs to be reduced to 50 per cent, similar to the way it was for CIPC, he emphasises. As with spearmint, an electrical fogger is recommended but other hot fog equipment may be used. After application, stores need to be closed for 48 hours, although internal ventilation is permitted. Applications need to be made every four to six weeks.

Jeroen says: “It is important that stores are at least 40 per cent filled with potatoes for the use of DMN or Biox-M (air ducts and plenum needs to be included in the calculation). This could be a problem for growers with large stores in years with poor yields , so it would be better over time to move towards using smaller stores that allow more flexibility.”   

Investing in fans which are capable of working at different air speeds on application may also prove crucial. “If you do not have the ability to slow fans down to 50 per cent, then your sprout suppressant will not be as effective, and may end up costing you more if further applications are necessary.”

Moving on to talk about storage of the future, he highlights the importance of stable temperature and the need for refrigeration to achieve it.

 “One of the challenges is that all the alternatives to CIPC are relatively new, so there is still a lack of information on how often they need to be applied, and the best store management strategy to deal with them.  We have found that the more efficient the store, the fewer applications that are needed.”

Update on storage research findings in the UK

“Once CIPC has gone after this season, the first thing we will need to be able us to use our stores is a temporary MRL (tMRL) for CIPC,” says AHDB research scientist, Adrian Briddon.  This is because CIPC residues are still found on crops held in previously-treated stores.

Work at SBCSR has contributed data to a concerted European effort to apply for the tMRL and it is hoped that the European authorities will grant this in early 2020. If granted, a value below 1 ppm is expected. UK trials have measured values up to 0.4 ppm.

Without chlorpropham (CIPC),  achieving effective sprout control on potatoes will become much more difficult, warns Adrian.

Options for the future are currently limited. UK-approved suppressants ethylene and spearmint showed low efficacy levels when used alone;  DMN and orange oil have not yet received regulatory approval.

Tests on sprout suppressants were set up by three seasons ago by AHDB, as soon as it became clear that CIPC renewal was seriously under threat.  This research includes treatments not yet available in the UK, in anticipation of potential future approval and an increased drive to understand the natural dormancy of potatoes on a variety by variety basis. These  included those with a shorter dormancy such as Maris Piper and Royal in addition to longer dormancy varieties Performer and VR 808, reports Adrian.

Another alternative, maleic hydrazide,  featured strongly in the Sutton Bridge work when used alone and in combination with other products. Results for Performer showed low residues, but also low efficacy, whereas Royal, which had 7-9ppm of residue had a better response to maleic hydrazide.

“Some varieties have responded better than others,” he says. “However, with MH, efficacy also depends on timing of application and the uptake of the canopy.”

Ethylene has often been dismissed for the processing sector because it can cause changes in fry colour.

“With experience, industry is getting better at using it, and while the fry colour can be darker, we think this is slight and transient.”

The suppressants BioxM and DMN are already approved in the Netherlands, and work well when crops are also treated with maleic hydrazide (MH).

Adrian says: “Maleic hydrazide will be very important to the future of sprout control.”

The work being undertaken by AHDB is not just on chemistry, and research scientist Dr Glyn Harper is leading experiments on the effect of dormancy.

Glyn says: “While we have information on how some of the older varieties react to different temperatures, the newer varieties are, as yet, relatively unknown.”

Temperatures for storing processing crops are typically 9 – 10 deg. C, but in the  mainland of Europe are moving to values lower than this, so trials are looking at storage at between 6 and 8 deg. C.

Head of Storage Research Adrian Cunnington points out that adjustments in storage will also have to be made; particularly in the older ‘leaky’ stores.

“To achieve optimum efficacy with these alternative sprout suppressants, stores have to go through an extended time of closure following application” says Adrian, adding that those with leaky buildings may need to consider an upgrade such as new louvres to ensure product efficacy.

Minimising the minimum number of applications will be key to margins, as the alternatives are much more costly, he emphasised.

Storage Costs

While the typical cost of an application of CIPC is around £1.20, maleic hydrazide is £2.00, ethylene £3.50, and mint oil £4.50. In-field application of maleic hydrazide before lifting will help keep costs down.

In a recent study tour to the Netherlands and Germany,  examples were seen where the properties of individual varieties were being exploited to aid storage.

“This included choosing varieties both for long dormancy, and for their tolerance to storage at cooler temperatures. We are looking at this ourselves through our dormancy-ranking research – as we aim to reduce our reliance on chemicals whilst maintaining or improving control over sprouting.

“Store control for the long term will need prioritisation of refrigeration over ambient air , and there is a need to establish flushing protocols and settings.

“If ethylene is used, it may  be necessary to link the fans to the generator system so that the system shuts off while ambient air is being ventilated.

“If you would like help with advice on your storage system, you can request a free one-to-one visit from one of our AHDB Storage Network partners.”

Explore the latest sprout suppression research in the storage hub by AHDB Potatoes

CIPC alternatives for the processing sector

CIPC alternatives for the fresh-pack sector

Maleic Hydrazide as a potato sprout suppressant

Source: AHDB here

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