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CIPC in cold stores: time to re-assess

24 September 2012

The advantage of an effective sprout suppressant like CIPC is that it works under most conditions at an affordable price and with minimal impact on the crop’s marketability. This means it has been a universal solution for control of sprouting in potato storage – even when the crop has been held at very cold temperatures – and could be easily applied and re-applied should the need arise. 

Until now.

 
CIPC, as many readers will know, has been under Stewardship for the last 4½ years. This was because the Advisory Committee on Pesticides alerted the industry to a concern about residue exceedances. CIPC has a Maximum Residue Level (MRL) of 10 mg/kg and, whilst the vast majority of potatoes have residues well below this threshold, five samples taken under statutory monitoring over the past three years have exceeded this limit.
 
A huge amount of work has gone into the Stewardship programme since 2008 to introduce new control measures for CIPC application and Best Practice has changed markedly, but the bottom line is that exceedances are still being found. This puts our whole industry under threat that the chemical could be withdrawn.
 
Follow up assessments where exceedances have occurred have identified cold stores as a concern. The need for CIPC in these potato stores should be small given that the level of sprout growth at temperatures below 4°C is normally very limited. The challenge arises when the distribution is too uneven as areas of the store with poor airflow tend to be deficient in CIPC and start to show some eye movement. This is taken as a need to re-treat but the reality is that there is more than enough CIPC in the store to control sprouting – it’s just in the wrong place. Moving it is difficult as the airflow is poor and, at low temperature, its volatility – the ability to move into the gas phase – is much reduced. 
 
The risk with re-treatment is that more CIPC goes to the areas of the store which are not deficient in CIPC and they could then exceed the MRL. So making more applications is not the answer. The solution is to sort out the distribution problem. Research has indicated that this is best achieved by moving to positive ventilation systems such as suction wall or letterbox stores. But, where this is not possible, action can still be taken to improve distribution.
 
Current best practice recommendations for cold stores are:
  • Go to the CIPC Stewardship website at www.potato.org.uk/cipc to access these Best Practice Guidelines.
  • Determine the need to apply CIPC in relation to variety, season, other chemical use and intended storage term.
  • Assess the suitability of the store using the Red Tractor Store Checklist. Copies can be downloaded from the website above.
  • At store loading, stack boxes evenly across the store blocking off any areas where short circuiting of airflow might occur. Use any form of positive ventilation (ideally with slow speed fans) to apply CIPC if available. Alternatively, create a plenum (a covered gap) within large blocks of boxes so that CIPC can be applied to this plenum and the fog moves directly into the pallet slots of the boxes. 
  • If treatment is deemed necessary, apply early. Do not use a dose higher than 14 g/t. Ideally, treat the store during pull-down when crops are cured but are still a little warmer than their ultimate holding temperature (7-10°C). Preliminary research results indicate that this optimises the application process and the availability of CIPC to the crop may be enhanced.
  • Don’t re-treat crops without considering the risk of exceeding the MRL very carefully. If in doubt, take samples for testing and consult with an NAAC-accredited CIPC applicator.
  • In general terms, avoid late treatments which could lead to higher residues on crops moving into the marketplace. 

Specialists at Sutton Bridge CSR are on hand to answer your queries on CIPC use on the AHDB Potatoes Storage Advice Line – call free on 0800 02 82 111.

 
Grower Gateway - Issue 7, 2012
 
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