PSI Bulletin: September 2025
No. 09/25 SUBSCRIBER EDITION
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Dear Subscriber,
Welcome to the latest Synopsis bulletin for September from Potato Storage Insight for all our regular subscribers.
In this month's edition, we have news of:
A report on our latest training output from PSI
Best practice: Current 'state of play' for harvest and store loading
Technical insight on Rubbery Rot (Geotrichum candidum)
Save the date for Strategic Potato Storage Day 2026
News of a new potato storage publication due out in November
Approval updates on the use of cylinder ethylene
PSI Activity
One-day potato store managers' training course
Eleven delegates joined us for our latest training output, a one-day, intensive course on potato storage management delivered ahead of the 2025 harvest. The event was held at the Greetham Valley Lakeside Conference Centre in Rutland.
Further training activity is planned for the first half of 2026. This will include our annual two-day residential course in March for which further details will follow soon. Discussions are also taking place for further regional training and, potentially, another round of BASIS Stored Potatoes courses.
Please get in touch if you have training needs and would like to be added to our waiting lists - email adrian@potatostorageinsight.com.
PSI will be exhibiting at the forthcoming BP2025 event being held on 19/20 November at Harrogate.
Best practice
Store loading
Harvesting has finally got underway in earnest as growers look to capitalise on September weather with ambient temperatures dropping away in recent days for the most part.
Progress with store loading has been very dependent on localised conditions; some crops went into store well at the start of this month whilst others had difficulties with bruising. This has meant some growers have had to hold back harvest until there is more rain, unless they have had irrigation available to put water on before lifting (below).
In other areas, particularly in the west, rainfall has been more intense so it's been a case of waiting until field conditions are suitable.
Best practice, as ever, requires close inspection of the crop before it goes anywhere near a store, especially given a significant number of reports of fungal rots (see Technical Insight). Consider ‘hot boxing’ some samples before store filling begins to make sure there are no hidden surprises awaiting you.
Generally, given the season, most crops are burnt down, skins are setting well and they're waiting to be lifted.
The downside of this is that extended periods in the ridge after senescence, especially if it's wet, can encourage the spread of black dot from the stems to the tubers. This can be a significant problem in fresh market varieties and warrants a fast pull-down of temperature to try to arrest the expression of the symptoms in storage.
In all crops, a plentiful supply of air will be needed to dry, cool and stabilise freshly-lifted material. If possible, get the fans on at night to do this. Use positive ventilation wherever you can.
Make sure you minimise temperature differences – such as the difference between what’s already in the store and what is being loaded - to avoid the risk of condensation. Remember! Warm moist air blown on to cooler potatoes risks re-wetting the crop you have already dried.
Take care if you are forced to suspend harvest due to bad weather. Keep air moving through the crop already in store but don’t cool it too much if warmer crop is going to be coming in from the field. Try to limit temperature differences to less than 4°C.
Don’t risk the integrity of your store by including any ‘rained on’ crop in the pile. Store wet potatoes separately, dry them as best you can using positive ventilation and don’t plan to keep them.
It goes without saying that it’s essential to keep damage to a minimum when harvesting. And any ‘minor’ nicks or scuffs will still need to be cured or there is a risk of infection. Diseases such as dry rot or skin spot will exploit any breach of the tuber skin but often won't be visible for several weeks to come.
For specific advice, call Adrian on 07970 072260.
Technical insight
Rubbery rot
Reports have been received of this relatively unusual disease affecting crops during this year's early start to the harvest.
Rubbery rot is caused by the fungus Geotrichum candidum. It is most commonly found inearly crops. Tuber symptoms are such that the potatoes are damp and feel rubbery when squeezed. The skin of affected tubers may have tufts of grey or white mycelial growth.
Often the whole tuber is affected but where the tuber is partially infected the skin shows irregular brown patches with characteristic dark margins. If freshly cut, the tubers exude water and may have a vinegary, sour milk smell; the flesh has a rubbery texture and can turn a dirty pink or, more often, grey colour after a few hours. Advanced rots may have cavities. There are no haulm symptoms.
Diseased tubers are frequently overlooked at loading as their distribution can be quite sporadic as often an infected plant has only one or two infected tubers.
The problem is more often noticed in store due a fishy smell and a dark liquid exudate.
Rubbery rot is mostly associated with wet soils and warm conditions approaching harvest.
Control is best tackled in the field as a long-term measure by ensuring adequate soil drainage. If a rubbery rot infection is suspected, take steps to store the crop separately and monitor it closely as secondary breakdown may follow.
SDF/PSI Strategic Potato Day 2026
As mentioned last month, arrangements are being put into place for SDF Agriculture and Potato Storage Insight to run a third Strategic Potato Storage Day in 2026, following successful events in 2024 and 2025.
The date that has been set is Wednesday 20th May. The event will be kindly hosted by Dyson Farming at its Leadenhall Farm site at Holbeach St Marks in south Lincolnshire. Further information will be released shortly.
New Potato Storage Handbook to launch at BP2025
The Potato Store Managers' Guide was first produced by the British Potato Council, under the authorship of Bob Pringle and Adrian Cunnington, back in 2001 with an update following under Potato Council oversight in 2008, reprinted in 2012. Another revision came along under AHDB cover in 2018/19, the third edition.
Now, in this post-levy era, the PSMG is no more, so Adrian at Potato Storage Insight has got together with British Potato Review to bring you a new reference; this is to be known as the Potato Storage Handbook. The new publication will be launched at BP25 at Harrogate in November, where it will be initially available free of charge. Please make a mental note to grab yourself a copy at the show (from the PSI or British Potato Review stands) and watch this space for more news in the coming weeks!
Ethylene clarification
There has been some confusing information circulating in the industry about the use of cylinder-based ethylene systems* in potato storage following some changes to ethylene's clearance status.
Jeremy Barraclough of BioFresh Safestore, who market the system for use in potatoes, has kindly provided the following update:
"This is to provide an update regarding the use of BioFresh SafeStore following the recently announced removal of ethylene as an active substance from the HSE database.
Please be assured that BioFresh SafeStore remains fully operational. This change will not affect this season for the following reasons:
When a substance is removed, there is a 6-month extension period before the end of the authorisation takes place, followed by 12 months to use up any existing stock. This means customers with BioFresh ethylene systems can continue to operate without issue this season.
Additionally, ethylene is covered under commodity chemical status until the 31st August 2027, which guarantees its permitted use until that time. However, it is expected to remain a commodity chemical because of its wide uses within industry. https://www.hse.gov.uk/pesticides/commodity-substances/commodity-substance-99.9percent-ethylene.htm
Looking ahead, BioFresh Safestore is already working to submit the SafeStore system for full approval again, ensuring continued long-term compliance and availability.
If you have any questions or would like to discuss how this applies to your setup, please don’t hesitate to get in touch.
Jeremy Barraclough
Operations Director, BioFresh SafeStore
07872 637328"
*For clarity, ethanol-fuelled catalytic generators are not affected.
Forthcoming events
If you are hosting a potato or agricultural industry event, please send details to admin@potatostorageinsight.com. Key dates for your diary with relevance to the potato sector in the coming months in UK and Europe include:
November
Sun 9 - Sat 15 Agritechnica - major agricultural machinery exhibition in Hannover, Germany https://www.agritechnica.com
Wed 19 - Thu 20 BP2025 - the British Potato Event, Yorkshire Event Centre, Harrogate
Exhibition, seminars and industry awards dinner on the Wednesday evening. Save the dates!
Details from: bpinfo@warnersgroup.co.uk
December
Tue 9 - Wed 10 CUPGRA Conference, Cambridge
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Synopsis is written by Adrian Cunnington and published by Potato Storage Insight Ltd., 45 Main St., Gedney Dyke, Spalding, PE12 0AJ. UK.
© Potato Storage Insight Ltd. 2025
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