Course: Potato management | Last Updates: 14th December 2015
Why have new limits on CIPC applications been introduced?
In 2007 a maximum residue limit (MRL) of 10 mg/kg was introduced across Europe for chlorpropham (CIPC), which the Advisory Committee on Pesticides (ACP) 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 Approval for use of CIPC came close to being withdrawn.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 limits agreed with ACP to ensure treated crops stay below the MRL. No more than 30g/t of CIPC can now be applied over a season to potatoes destined for the fresh market. The maximum dose for processed potatoes, including those used for peeling, is 50g/t.
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. 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.
- If you usually use a formulation that keeps you from applying early, and have experienced sprouting problems early in storage, consider switching formulations.
- 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 wel 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.
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?
The most efficient way of using CIPC is in a bulk store fitted with a variable frequency drive (VFD), or inverter, to lower the fan speed and recirculate the fog. Crops with the greatest CIPC requirement are best kept in such a store.
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.
What steps can be taken to improve distribution in box stores?
Box stores can present a challenge. Using CIPC in an overhead-throw box store is where it is hardest to achieve even distribution. Without remedial action, there is a tendency for fog to collect in the roof space and then settle on to the top of the crop below.
Distribution can be enhanced by effectively limiting the amount of fog entering the headspace using a plenum (see diagram 1).
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.
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 8-10 boxes deep for effective drying. Suction wall systems are more suited to stores with more than 10 boxes per row. CIPC is also best applied via the letterbox, but don’t use fans unless their speed can be reduced.
Three Golden Rules for CIPC best practice
- Timing – Don’t delay, always apply first application before ‘eyes open’ stage.
- Dry, clean crop – remove as much mud as possible and ensure crop is dry before applying CIPC.
- Airflow – Stack or load store to ensure an even distribution of fog. In bulk stores, low speed recirculation improves distribution and reduces CIPC requirement.
Potato Council publications
- AHDB Potatoes store managers’ guide
- AHDB Potatoes improving the use of CIPC in bulk stores
- PICSG CIPC application checklist
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