Best practice - Box
Effective treatment of potatoes stored in boxes requires a range of approaches depending on the type of storage system being used.
The major factor dictating the way CIPC is applied is whether or not the store has positive ventilation, i.e. whether the ventilating air (and fog) can be forced through the potatoes, rather than simply pass around them.
It is crucial that temperature in any store is as uniform as possible prior to treatment. This requires the air to be recirculated around the store (without cooling) ideally overnight but for a minimum of 6 hours before the application is made. Do not apply CIPC immediately after cooling has been taking place as there is a high risk that deposition will be uneven.
Low temperature stores
Most of the MRL exceedances that have been detected during the period of CIPC stewardship, have been found in low-temperature, fresh market supplies. AHDB funded research indicates this higher risk is associated with the reduced volatility of CIPC at low temperature. This may also explain the relative lack of efficacy of CIPC at low temperature. For the 2016-17 storage season, all CIPC Approval Holders strongly recommend that, where necessary, just one application of CIPC is made to potatoes that are stored at a temperature below 5°C, and this should be applied within three weeks of store loading, before store temperature is reduced below 7°C.
In stores with true positive ventilation (e.g. letterbox and suction wall/Aspire systems), the store ventilation system should be used to recirculate CIPC fog. As with bulk stores, it is recommended that this is done with fans operating at low speed, controlled through an inverter (variable frequency drive) and any refrigeration systems should be by-passed and/or sealed off to eliminate the risk of the coil being blocked. Recirculation should take place for the duration of the application and until the fog has cleared. Fans should be operated at the minimum speed required to prevent fog accumulating in the store headspace.
Non-positive ventilation (overhead throw stores)
Most box stores in GB are of the overhead throw (OHT) type. With this system, air is displaced by fans above the boxes and moves around the crop rather than through it. In this type of store, without corrective action, there can be an increased risk of higher CIPC residue levels occurring on potatoes in top boxes.
Where it is used, CIPC should be applied via a plenum (see Figure 1) to prevent fog rising directly up into the store headspace. This limits the deposition of CIPC on surface boxes, reducing the risk of an MRL exceedance. Penetration of fog into boxes with this system will be less, compared with positively ventilated stores, and efficacy of sprout control may therefore be limiting.
Where the construction of new stores is being considered and it is anticipated these could require application of CIPC, the incorporation of positive ventilation is strongly recommended. It is anticipated that the extent to which CIPC can be used in overhead throw stores may be limited in the future.
Figure 1: CIPC application plenum in an OHT box store made by covering an inspection corridor through a block of boxes.
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 & safety regulations are complied with during installation, and where access to top boxes is required.
USE PLANT PROTECTION PRODUCTS SAFELY. ALWAYS READ THE LABEL AND PRODUCT INFORMATION BEFORE USE.