Chlorpropham (CIPC), the go-to sprout suppressant for the majority of potato growers across Europe, has been banned in the EU.

The Union published the regulation in June that requires member states to withdraw authorization for CIPC-based products by January 8, 2020 and ensure all existing stocks are used up by October 8, 2020.

These dates represent the upper limits of what member states can choose and it is now down to each country to set withdrawal and use-up dates within those limits. The Commission decided to not renew the approval of CIPC because of concerns around dietary risks for consumers eating CIPC-treated potatoes.

While the ban of CIPC in the EU has been in the works for months and was expected within the industry, finding viable alternatives is not easy. Even so, a few options are available, for example, ethylene gas or green mint oil, but each comes with its positives and negatives.

Dirk Garos, director Technical Systems at Restrain, a company which markets ethylene gas-based solutions for potato storage, says that the firm anticipated the CIPC ban and so managed to prepare more efficient production of their equipment. Using 20 years of experience, Restrain came up with the latest design and technology to make the solution even more easy to apply. The company’s machines are now so-called autonomous plug-and-play systems, with installation being no more than five minutes. A system is made up of a Restrain Generation and sensor, which supply a very low concentration of ethylene gas. This dynamic gas weights roughly the same as air. Hence, it can spread all over the potatoes, regardless of whether they are stored in bulk or containers.

When asked what the advantages of using ethylene gas are, over other alternatives like green mint oil, Garos says that ethylene-treated stored potatoes can be processed immediately, without any waiting time. By comparison mint oil-treated potatoes need two to four weeks waiting time before they can be processed.

“What’s more, ethylene gas produced in situ is four to six times cheaper. It’s the safest gas, which leaves no taint or smell. The dynamic gas is continuously kept on a very low concentration, until the end of the storage season. Operators do not require a closed or sealed cold store, as the Restrain equipment is designed for compensation on storage leakage. The daily flushing to keep CO2 levels low is not an issue, since ethylene uptake by receptors in the potatoes keep the spuds dormant for three days,” further explains Garos.

Speaking of which, AHDB has been exploring a more holistic approach to tackle the challenge of storing potatoes. One of its projects aims to determine and increase industry awareness of the dormancy of different potato varieties, in a bid to answer the question: Can the industry use the dormancy of potato varieties for long-term  storage in the post-CIPC era? Currently, information on the expected dormancy period for potato varieties – the period before sprouting begins – is both sparse and conflicting, meaning growers are compelled to use a one-size-fits all approach, when applying sprout suppressants.

“What we are looking to do is improve the efficacy of sprout control and reduce costs by using longer dormant cultivars. Varieties are not all interchangeable, but sectors and customers will have a range, and it’s within this range that we are looking to gain advantages,” said Adrian Briddon, storage senior scientist at Sutton Bridge Crop.

He goes on to say that it isn’t all down to dormancy either. Sprouting pressure and sprout suppressant requirements are also related to storage temperature. When information on low temperature tolerance is available – the ability to hold varieties at lower temperature without accumulating fry color damaging reducing sugars – then will the industry be able to practice integrated control of sprouting and minimize the use of post-harvest treatments.

The project makes use of AHDB’s Strategic Potato (SPot) Farm network: Sutton Bridge is currently overseeing trials at two SPot farms, looking at the dormancy characteristics of up to 40 popular varieties, as well as some new entrants to the market.

In the context of the upcoming CIPC ban, it is also worth noting is that recently, the restriction on the use of products containing Maleic Hydrazide (MH) has been removed, following a review by the Chemicals Regulation Division (CRD) of the HSE. But it is a viable alternative?

AHDB’s own review of MH states that reductions in the permitted treatment rates for CIPC have driven an increase in MH use in recent years. A total of 20,000 acres (15% of all crop) was treated in the UK in 2016 and there was some reversal of previously limited acceptance of MH use within fresh market crops for some markets, notably for short dormant varieties.

In recent trials, combinations containing MH, used in conjunction with other active substances have performed better than single products alone. Combination treatments including MH were also exclusively used in commercial processing stores visited in mainland Europe in spring 2019. This included stores of up to 4,000 tons capacity using BioxM (spearmint oil) or 1-4 Sight (dimethylnaphthalene).

Basically the conclusion was that MH as a stand-alone treatment does not always completely prevent sprouting but, providing it is applied correctly, it gives good control in situations when potatoes are stored for short periods and the risk of sprouting is low.

In conclusion, while registered alternatives are becoming available, there are still industry concerns over efficacy, cost and potential taint issues (a key problem for end product flavor and consumer acceptability). Therefore, the quest for finding the ultimate CIPC replacement continues on.

Update: Following the publishing of this article, Potato Business was contacted by a Juno (Plant Protection) representative, which has been distributing spearmint oil in the UK for the potato market for the last 7 years. The company’s Director Nick Tapp clarified a few points. For example, he stated that Biox-M has no harvest interval, as crop treated with it may be removed from store immediately. The product is safe. However, there is an advisory retention period of up to 12 days in store to allow the naturally occurring odor to dissipate. It should be noted that it would seem wasteful to treat a crop immediately before removal for further processing.

According to Tapp  spearmint oil (marketed as Biox-M) is highly effective in the control of sprouting in potatoes in stores. Crops do not begin to sprout on removal from store following treatment. Moreover, Biox-M has worked well with all varieties treated to date. Normal variety dormancy appears unchanged (very dormant varieties take longer to recommence sprouting).

Lastly, Tapp says that Biox-M is approved for use on organic crops, and is suitable for use in multi-use stores. Crops treated with Biox-M have reduced weight loss in store and unlike CIPC, it leaves no residue in buildings and boxes.