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POTATO NEWS
With no single alternative to the withdrawn CIPC, a combination of techniques will be needed for crops going into long-term storage this season
Words by: Spence Gunn
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The start of this year’s storage season marks a sea-change for potato growers. Withdrawal of approval for CIPC means the industry has to adapt to a different way of suppressing sprouts.
Growers of processing potatoes will, of course, be most affected because of the length of time their crop is in store – and they have relied on CIPC for decades.
“There’s no other product that’s a straight replacement,” says Adrian Cunnington, head of AHDB Potatoes’ Sutton Bridge storage research unit. “It’s a question of changing the management approach and using a combination of techniques.”
There is one new sprout suppressant, however, that many in the industry feel does come close to the performance and practicality of CIPC.
DMN (1,4-dimethylnapthalene) is widely used in the USA and already approved at EU level. It has been available to Dutch growers since 2015 and was registered in Germany, France, Poland and Ireland two years ago – but UK growers are still waiting.
DormFresh, which markets DMN in Europe, is seeking full UK authorisation, but the process is unlikely to be complete until next year.
The company, meanwhile, has been working with AHDB, the NFU and other industry bodies on an emergency approval so that DMN can be available at least to some growers this season.
“The first submission, earlier in the summer, wasn’t acceptable because it was asking for too high a proportion of the national crop to be included for treatment,” says NFU horticulture and potatoes adviser Rupert Weaver.
“This has put the industry in an awkward position of deciding who should and should not have access to DMN, and whether we should prioritise certain processing supply chains, such as crisping or chips, or particularly sprout-susceptible varieties within the processing sector.
“The difficulty is finding a solution that’s fair to growers and acceptable to the Chemicals Regulation Division.”
The latest application for emergency authorisation was submitted at the beginning of August, as this edition of Horticulture went to press. Mr Weaver hopes a decision might be made in time for growers to start treatments as crops begin to arrive into stores.
THE ALTERNATIVES
Should some form of emergency authorisation be granted for DMN this year, it will still be out of reach of most growers. For them, sprout control will depend on the three alternative treatments currently available in the UK so far – in-field application of
WHAT IS DMN?
DMN is a synthetic copy of a volatile compound that occurs naturally in potato tubers.
It inhibits sprouting by maintaining the tuber in a dormant state and has already become an important part of store management for growers in Europe.
maleic hydrazide, and in-store treatment with ethylene gas or spearmint oil – although each has its own drawbacks, including cost.
“Maleic hydrazide is definitely part of where we will be going, but we still need a better understanding of the best way to use it in the field to get tubers off to a good start in storage,” says agronomist and NFU Potato Forum member Andy Alexander.
“Managing the application is critical. It’s about attention to detail, making sure you apply it when the crop isn’t under stress, and using it early enough – applications should have gone on at least six weeks before desiccation. It’s also important to make sure your buyers are comfortable with it.”
He says treatment is most effective
AHDB RUNS THE RULE
AHDB has been running trials on storability of both processing and fresh market varieties treated with either spearmint oil or ethylene, and in each case, with or without a growing-season application of maleic hydrazide.
So far in the trial on fresh market varieties, maleic hydrazide alone has looked helpful in controlling sprouting in sproutprone King Edwards and Maris Piper and helped significantly with the less ‘sprouty’ varieties Melody and Nectar.
In the absence of maleic hydrazide, spearmint oil and DMN resulted in sprout-free Maris Piper after nine months’ storage at 4.5°C, though Sutton Bridge senior scientist Glyn Harper says DMN performed best overall, while ethylene treatment cut sprout length to less than 5mm compared with 25mm on untreated tubers.
on an overcast day, at temperatures below 26°C, ahead of a 24-hour period when the spray can dry. Early morning or late afternoon or evening are the best timings. “Application needs to be at full rate,” he adds. “But the 400-to450 litres per ha required can be a challenge when you may be busy with, for example, cereal harvest.”
For growers who aren’t routinely testing for residues – applications are subject to an maximum residue level (MRL) – Adrian Cunnington says it’s worth it on tubers going into store. An effective application should result in at least 12mg per kg in the tuber, which will suppress sprouting up to Christmas or into January, depending on the variety, storage temperature and store management techniques.
TRIALS AND TEMPERATURE
Growers for the fresh market have more leeway to use low-temperature storage to control sprouting, says Mr Alexander. To avoid the need completely for a sprout suppressant, however, temperatures must be lower than 3°C, levels at which sugars can build up, affecting aspects of quality such flavour, texture and roasting colour.
Growers might also need to work with customers on variety choice to maintain supply through the storage season. AHDB trials compared the storage life of 40 varieties at 15°C, finding a difference of more than three months between the quickest, King Edwards, and slowest, Desiree, to sprout. There was a difference of around 60 days between processing varieties – the quickest to sprout was Royal, the slowest was Markies.
Longer term, the industry would benefit from more cold-tolerant varieties, as well as varieties that are inherently dormant for a longer period.
Store performance itself also has a part to play so checking insulation and preventing air leaks that could result in escape of volatile sprout suppressants will all contribute. P
