Tuesday, August 20, 2019

Active recirculation key to good potato storage

October 31, 2017 by  
Filed under Crops

In-store applications of sprout suppressant Chlorpropham (CIPC) must now be made using active recirculation, growers are reminded.

Active recirculation refers to industry-agreed guidelines that describe the re-circulation by fans of air containing CIPC fog to optimise the efficacy of European lower maximum dose rates, says Mike Storey, chairman of the Potato Industry CIPC Stewardship Group.

About 4m tonnes of the UK’s 5.5m tonne annual potato crop are stored each year, with much production kept in store for as long as it is in the ground. About half the UK industry uses CIPC as a sprout suppressant.

As potatoes need to be stored at a relatively warm 6-13ºC to maintain frying quality, sprouts will grow very easily. Usually applied to stores by dedicated fogging contractors, CIPC can maintain high quality potato tubers for up to a year.

To reduce weight loss and dehydration, however, stores must have strong airflow across and around the crop. Ventilation equipment should have up-to-date temperature control, and efficient refrigeration to reduce drying the time to dry and cure a wet crop.


All potato store owners must comply with new legislation stating that CIPC applications must not exceed the maximum total dose rate of 36g/tonne for potatoes produced for processing and 24g/tonne for those sent to the fresh market.

Alternative sprout suppressants available in the UK include ethylene. Applied as a gas using in-store equipment, it has relatively high loss from the store but provides completely effective sprout control at low temperatures.

Spearmint oil (active ingredient R-carvone) received full UK registration in 2012 and is used in some pre-pack supply chains. But it can be costly for processing stores. Oil can rapidly burn back existing sprouts and it has been used for recovering commercial packing crops in this way.

Maleic hydrazide is a systemic growth regulator applied to crop foliage in the field. Able to control volunteers, uptake depends on field conditions but effective applications can replace or reduce the need for CIPC. Not acceptable in all markets, it is controlled by a 50ppm Maximum Residue Level.

The AHDB storage research centre at Sutton Bridge has also researched products used in the USA, the Netherlands, Belgium and Austria. They include 1,4-dimethylnapthalene (DMN), 3-decen-2-one, caraway oil (active ingredient S-carvone) and clove oil (active ingredient eugenol).

Research has also included how to best achieve the active recirculation of CIPC in box stores, partly because so many are fitted with passive rather than positive ventilation.

One Lincolnshire farm supplying the chipping sector has fitted out a new lateral suction store with fans and inverters to ensure consistent applications of sprout suppressant, said Sutton Bridge manager Adrian Cunnington at the AHDB’s recent post-harvest event.

CIPC is applied in each unit as a fog directed by the fan system along the store and drawn through the boxes towards a covered suction void. A sheet is placed over the space between the boxes to create this void and ensure air is sucked uniformly through each box before it is re-circulated.

Inconsistent airflow

But problems remain with overhead throw box stores, which are prone to inconsistent airflow caused by short circuiting in different places. Such stores are no longer deemed suitable for CIPC as they are not capable of active air re-circulation without being modified.

Tests aimed at evaluating a number of scenarios for improved airflow distribution have been made possible by the construction of a small-scale model store at Sutton Bridge. The researchers have found a good deal of variation said Mr Cunnington.

“We found that just 31% of the air reached the front of the store in a standard set-up while adding a curtain or plenum gave us an instant step change in getting more air around the store, increasing the figure to 79%. Variability of airflow was also halved.”

Inviting new thinking from store managers, Mr Cunnington added: “Airflow is proving more challenging than we expected but thanks to the new modelling system we’ve been collecting date on a range of options to evaluate what works best.”