The Future of Effective Sprout Control

Chlorpropham (CIPC) is long established as the major global sprout suppressant, but whilst EU regulations tighten, the team at Sutton Bridge Crop Storage Research (SBCSR) has been evaluating new alternatives.

Effective sprout suppression is a fundamental component of managing stored potato quality. Great Britain is heavily reliant on Chlorpropham (CIPC), which has been available for over fifty years and was in place even before refrigeration/temperature controlled storage was an option to growers.

CIPC is used in approximately 94 per cent of all post-harvest sprout suppressant applications in GB and inhibits sprout development by interfering with cell division. The maximum application rate is currently 36g/t for fresh market and 63.75g/t for processing potatoes, which is expected to reduce over the next few years.

In recent years alternative treatments have been made commercially available that can replace or complement CIPC. The team at Sutton Bridge Crop Storage Research (SBCSR) has been at the forefront of evaluating these.

Speaking at AHDB Potatoes 2013 storage forums, SBCSR’s Adrian Briddon and Ajay Jina discussed new treatments and their potential for use in place of, or in combination with CIPC.

“The aim is to understand how store managers can gain enhanced control, whilst reducing associated residues,” explained Mr Briddon. “There are some very interesting alternatives coming through at different stages in the pesticide registration approval process.

“The new products require a different store management approach and a specific understanding of their application. CIPC is a solid with long-lived residues, added Mr Briddon.  “The new generation of sprout suppressants tend to be either gases or volatile liquids, which gives far more flexibility in building use.” 

Stores where CIPC has been previously used, restrict the 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 it allows 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.

In Great Britain, CIPC is applied as a hot-fog with a fossil fuel (petrol or LPG) used as the energy source. During the process, ethylene and carbon dioxide are produced from combustion of fuel, which can cause deterioration in processing quality. Therefore, after 6-8 hours when the CIPC fog has settled, fresh air is circulated into the stores to mitigate against any negative impact on fry colour.

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 twenty four hours is likely to be a minimum label requirement, so for processing store different types of equipment are likely to be used.

Alternatives currently available in the UK

Ethylene has been available for a few years and the 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 ingredient 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. Spearmint oil has been reported to have been used successfully on commercial packing crops in this way.

Biox-M 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.

Alternatives that may become available in the UK

1,4-Dimethylnapthalene (DMN) (1,4-SIGHT™) has been available in the United States of America for many years. Registration in the EU is currently being sought and it will probably be registered in the Netherlands first, hopefully in 2013/14, and the UK thereafter.

DMN is effective in both pre-pack and processing stores, with potential to replace CIPC. 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.

3-decen-2-one was identified in research at the University of Washington and is being commercialised by Amvac. It was already approved as a food additive and has just received US registration as a sprout suppressant (SmartBlock™) in February 2013. It is exempted from an MRL (Maximum Residue Level) in the USA. EU registration trials are currently underway.  3-decen-2-one is a volatile, oily liquid and is likely to be applied by contractor as a hot-fog.

Caraway oil (active ingredient S-carvone) is available for sprout control of seed crops in the Netherlands as Talent. It is an effective suppressant and an EU registration, for seed and ware crops, is being developed by Makhteshim Agan. Low volume applications may be carried out weekly using equipment installed in-store and operated by the store control system.

Clove oil (active ingredient eugenol) has several registrations in the USA for use as a sprout suppressant and as a remedial treatment for crops where sprout control was incomplete. Plans for potato storage treatments, using clove oil, in the UK are not known.

To understand more about the new generation of sprout suppressants call the free storage advice service at SBCSR on 0800 02 82 111. For further information on CIPC, visit the CIPC Stewardship Group Website at: www.potato.org.uk/cipc.

CIPC application rates have been revised since this article was first published - for the current rates visit www.cipccompliant.co.uk