Alternative Sprout Suppressants

Globally, CIPC has been the sprout suppressant of choice for over fifty years. Research has been on-going however, looking for alternatives. This effort is bearing fruit, with a range of compounds identified and now at various stages in the regulatory process.

CIPC is a solid at room temperature – this is why residues, on potatoes and in stores, are so long-lived. Most of the new alternative sprout suppressants are volatile, oily liquids and one is a gas. These compounds will require a different store management approach and a specific understanding of the application conditions required.

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, treatments can have a modifying effect on stem numbers and some are being used successfully in seed management. In addition, some of the essential oils are also reported to control some pathogens.

In Great Britain CIPC is applied as a hot-fog, usually with combustion of a fossil fuel (petrol or LPG) used as the energy source. During the process, ethylene and carbon dioxide are produced from combustion of fuel. This causes deterioration in processing quality and therefore stores are flushed with fresh air as soon as fog has settled (6-8 hours), to mitigate against any negative impact on fry colour. Because they form vapour in store, many of the new sprout suppressants need longer store closure periods after application, to ensure complete ‘uptake’ of products. In many cases 24 hours is likely to be a minimum label requirement, so for processing stores, different types of equipment are likely to be used. The new products tend to be more dynamic compounds, being gases and vapours. This may mean applications need to be more frequent, but buildings can subsequently be used for storage of other commodities and seed potatoes. This is not the case with CIPC, where a risk of cross-contamination persists for many years.

Alternatives available in the UK

Ethylene has been available for a few years. It is a gas, so losses from store are 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 AHDB supported research at SBCSR, primarily to establish varietal sensitivity and 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.

Maleic hydrazide is a systemic growth regulator applied to foliage of crop in-field. It is useful for ‘volunteer’ control, but uptake is dependent on field conditions. Effective applications can replace or reduce CIPC requirement. It is not acceptable in all markets and is controlled by a Maximum Residue Level (50ppm).

Spearmint oil (active ingredient R-carvone) received full UK registration (BIOX-M, MAPP 16021) in 2012. Spearmint oil is being used successfully in some pre-pack supply chains but, in processing stores, is likely to be cost-prohibitive.

Spearmint oil can rapidly burn back existing sprouts. Spearmint oil has been reported to have been used successfully for ‘recovering’ commercial packing crops in this way.

In the pipeline

1,4-dimethylnapthalene (DMN) (1,4-SIGHT™) has been available in the United States of America for many years. DMN is EU Annex 1 listed and has received national registrations in The Netherlands, Belgium, Germany, France and Austria. UK registration has yet to be approved.

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.

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 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. It 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. In the Netherlands, 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.

Orange oil was EU 'Annex 1' listed in 2014. It is being developed as a sprout suppressant by Arysta Lifesciences . Arysta also have approvals for CIPC and maleic hydrazide. The active substance in orange oil is limonene and it is anticipated to be available in the UK in 2019. It is a volatile, oily liquid and likely to be applied by contractor as a hot-fog.

To understand more about the new generation of sprout suppressants call Sutton Bridge Crop Storage Research on: 0800 02 82 111.