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Potato storage

Course: Potato management | Last Updates: 1st June 2017

 
Adrian Briddon
Technologist
Sutton Bridge Crop Storage Research
Biography >>
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Why have new limits on CIPC applications been introduced?

In 2007 a maximum residue level (MRL) of 10 mg/kg was introduced across Europe for chlorpropham (CIPC), which the Advisory Committee on Pesticides (ACP), now the Expert Committee on Pesticides, identified as there being a risk of exceeding. Approval for use of CIPC came close to being withdrawn.

The message is clear: Use the sprout suppressant more responsibly or risk losing it altogether.

In response, a new Potato Industry CIPC Stewardship Group has implemented a series of reductions since 2012, agreed with ACP, to ensure treated crops stay below the MRL.

The ultimate aim is to bring the total dose down to 36g/t for the 2017-18 season. For the 2016-17 season, the new statutory total doses for CIPC are:

Fresh market: 24g/t of potatoes

At a store temperature of 5C or less, only a single application, up to 16g/t, should be made, before the temperature is reduced below 7C

Processing market: 42g/t of potatoes

 

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Why are residues such a concern with CIPC?

The vapours from microscopic particles of solid CIPC, applied as a fog, suppress sprouts and keep the crop in good condition. But because treatment is post-harvest residues will always be detectable.

While washing and peeling removes 90% of any residues that may remain on the crop, it is essential to ensure they are as low as possible to start with.

Fogging means distribution around the store and effectiveness varies, depending on crop condition, airflow, store design and climatic conditions at the time of application.

If good practice is not followed, in terms of both store management and application, some of the crop within a store can potentially receive a higher dose of CIPC than anticipated. Repeat applications could lead to an MRL being exceeded.

Extra care is needed because there are no alternatives for CIPC – the processing sector in particular relies on its use.

What can be done to minimise residues?

Don’t make first application too late. The ideal time is before the ‘eyes open’ stage. If sprouting has started when the first application is made, rates will likely need increasing as you play catch-up. In long-term stores, the crop could then easily reach maximum total dose before it is due to be unloaded.

Plan CIPC programmes as the store is filled and book contractors in advance. Crops stored for processing should have cured and be ready for first application after just two or three weeks. Forget the six week adage – in processing crops dormancy may well have broken by then.

Don’t delay first application until temperature pull down is complete, especially in ambient stores. It is more important to apply CIPC to a dormant crop than a cool crop, whatever the contractor thinks. Delaying may increase application rates.

Check crop condition regularly through the season and prepare well in advance for following applications.

What steps should be taken to prepare the store and crop?

Aim first for a clean, dry crop. Soil acts as a barrier to the CIPC vapour, allowing sprouts to grow, while a wet crop can suffer from scorch. Load the store quickly to ensure the last of the crop to come in will have cured before CIPC needs to go on.

A common problem is sprouting starting in the first loaded crop, driving the CIPC timing. If the back corner of the store is usually where most sprouting problems are found, this is not necessarily a CIPC distribution problem. It’s a management problem and needs attention.

fogger-final

In future, focus loading activity to a single store or, perhaps, only load crops treated with maleic hydrazide first. If there are no alternatives, concede that the store is too big for your operation and aim to get the building sub-divided into manageable units where CIPC can be applied more effectively.

Another point to consider is whether the potatoes are suitable for long-term storage. A marketing strategy rethink may be necessary.

Cooling equipment should always be switched off well before application, but keep fans running to even out the store temperature and reduce the risk of condensation.

Finally, make sure the store is well sealed and apply on a calm day. Any product lost from the store is a waste, and means less effective application and possible sprouting problems later in the season.

What roles do airflow and ventilation play?

Air recirculation has a key role to play in reducing the risk of exceedances by preventing hot spots. With this in mind, from 2017-18 crop, any store requiring a CIPC application must have an appropriate fan system installed to facilitate the active recirculation of air within the store.

Effectively this means that unmodified overhead throw stores will not be acceptable for 2017 or beyond. In a bulk store, this consists of active recirculation of airflow through the stack. Reducing airflow velocity (compared with normal ventilation) is recommended when applying CIPC and can be achieved by using variable-frequency drives (or inverters) or other suitable means.

When recirculating fog in bulk stores, it is important to balance the airflow by adjusting the inlets to lateral ducts. Don’t recirculate CIPC fog with fans running at full-speed as this could lead to heavy deposits on the fan blades, not on the crop.

monitor crop

What steps can be taken to improve distribution in box stores?

Box stores can present a challenge and will need to be modified if intending to use CIPC on 2017 crop and beyond. That’s because without remedial action, there is a tendency for fog to collect in the roof space and then settle on the top of the crop.

Fog in the roof space can be limited by applying into a plenum, (see diagram 1), but from 2017, an active recirculation system will also become a requirement.

It is vital to consider airflow when loading a box store. Ensure pallet slots are aligned to encourage fog movement into blocks (see letterbox duct illustration (diagram 2)).

If you have a history of poor sprout control in the centre of blocks, sub-division of the block will be worthwhile, by inserting corridors across the airflow direction. Note that CIPC gains access to blocks of boxes through the pallet apertures.

Box-clever distribution solutions

Plenum – A fogging port is installed to align with an inspection corridor, through blocks of boxes. The area between blocks is then sheeted over, from ground level, over the top and back down the opposite side, leaving a gap into which CIPC is fogged. Ensure health and safety regulations are complied with during installation, and where access to top boxes is required.

cipc plenum illo

Letterbox – Air will always try to take the path of least resistance, so letterbox ducts, lined up with pallet slots, can be used to force airflow through the crop.

Limit such systems to 7 or 8 boxes deep. Suction wall systems are more suited to stores with more boxes than this. CIPC is best applied via the letterbox, with fans at reduced speed.

potato

Three Golden Rules for CIPC best practice

  1. Timing – Don’t delay, always apply first application before ‘eyes open’ stage.
  2. Dry, clean crop – remove as much soil as possible and ensure crop is dry before applying CIPC.
  3. Airflow – Stack or load store to ensure an even distribution of fog. In bulk stores, low speed recirculation improves distribution and reduces CIPC requirement.

AHDB Potatoes publications

AHDB Potatoes Store Managers’ Guide

Best Practice Guidelines for the use of CIPC PICSG Store Checklist

Download at www.cipccompliant.co.uk or order by calling 08000 282 111.

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