As featured in Arable Farming Magazine March 2021
How CIPC is being replaced in processing potato stores
by Arable Farming
One season in, how have potato growers, especially in the processing sector, coped without CIPC in potato stores? Mike Abram reports.
Losing CIPC to suppress sprouting in store has created possibly the biggest agronomic challenge for potato growers from all the product withdrawals in recent seasons.
The processing sector has been hardest hit, where the crop is typically stored at higher temperatures and other products are largely untested, says Adrian Cunnington, head of crop storage research for AHDB Potatoes at Sutton Bridge.
“We’re in completely uncharted territory,” he says.
Initial feedback from potato store managers is the new solutions are working ‘okay’, he says.
“But the challenge of getting good sprout control is no longer straightforward.” Use of maleic hydrazide (MH), which helps delay the early dormancy break in potatoes, has dramatically increased from about 15-20% of the stored crop being treated to an estimated 80-85% this season.
“MH has provided the foundation of sprout suppression for a lot of growers.
It’s been important as it gives some residual control, which is the big difference with the new generation of sprout suppressants, which have much less residual effect than CIPC.
Efficacy from MH has been good through growers understanding how important it was likely to be to overall success, paying attention to application technique, erring on the side of uptake rather than yield and applying a little earlier, he suggests.
Most processing growers have then followed with spearmint oil applications, after 1,4-dimethylnaphthalene (DMN) only gained an emergency approval for a limited use.
The other alternative, ethylene, is technically challenging to use in the processing sector as it has been shown to have a negative effect on fry colours.
“For some varieties, growers have been applying mint oil since November, while others only from January,” says Mr Cunnington.
Timing those applications has been a learning curve, he adds.
“Advice from the approval holder is to go in just when the crop is starting to peep or show small sprouts.
“The difficulty is some people have perhaps gone in a little early and burnt off those small sprouts to begin with, but then found that another flush comes quite quickly behind that.
“It’s a balance between not going too early or too late.
The mint oil works by contact action, so it needs some sprout there to burn the growth back in each bud.
“It’s a challenge to achieve and I have heard varying reports about how well people have been able to do that.
“There is quite a lot of industry experience from contractors using mint oil in the fresh market, but the warmer storage temperatures in processing mean you end up having to re-treat more quickly.
“I’m aware of people who have already done several applications by the end of January and that’s starting to get expensive when you’re paying £4/t plus per application.” In the fresh sector, growers are more reliant on refrigeration for sprout control, storing at lower temperatures, supplemented by the use of MH.
“Where they were using CIPC, it was compensating for poor attributes of the store.
“Those issues remain so some will have used mint oil, but it should be possible to store most fresh market crop in the medium term without using too much chemical.
The extra cost of using mint oil is likely to drive further improvements to stores in the next few years, including the addition of more refrigeration.
“It changes the dynamic of the financial calculation,” says Mr Cunnington.
In the field James Fretwell, Monkham Bridge Farm, Doncaster
Storing potatoes long term is crucial for the success of J.and J. Fretwell Farming, which primarily supplies potatoes for the fish and chip shop market allyear-round, with storage utilised from mid-September to July.
The business has around 7,000 tonnes of box and bulk storage split between a number of older stores usually unloaded first, to a relatively new 2,500t box store, which with better airflow and ventilation allows for storing crops into July.
Before CIPC was deauthorised, James Fretwell says the business typically applied maleic hydrazide (MH) to all 150 hectares of potato crop to both suppress sprouting in store and help prevent groundkeepers from growing in a following crop on rented ground.
“We would then use about three applications of CIPC, with the first one applied as soon as temperatures were pulled down in store about a month after harvest, which would see us effectively through a whole season at very little cost – about £1-£1.20/t per application.” This season, without CIPC as an option, MH was applied over a 10- to 14-day period in midJuly, he says.
“It’s not an easy product to use, but as we knew we had lost CIPC we took even more care to apply it in optimum conditions.”
Timing has to be carefully judged as a compromise between yield and getting enough MH into the tubers to be effective.
“Before we apply we sample dig.
It stops any tubers below about 40mm from growing so you don’t want a lot of small tubers as you’ll hit your yields.
You’re trying to predict desiccation and harvest dates and work back three to five weeks from there.” Application is also important.
Mr Fretwell uses a higher water volume of 300-350 litres/ha and scrutinises weather forecasts to make sure there is at least 24 hours of dry weather following application.
“We also try to apply in cooler weather, so early evening into the night when the potato crop is least stressed.
MH can knock the crop back if applied in direct sunlight.” That care has paid dividends, with stored crops only being treated in late-January with spearmint oil in three stores, when the potatoes’ eyes opened.
“The first application has done a reasonable job of burning sprouts off,” Mr Fretwell says.
Applications of mint oil work out around £4-£4.50/t, with repeat applications as and when needed, most likely every five to six weeks, he believes.
“CIPC cost us around £3.60/t for the season, this is more likely to be £17-£26/t.” It is a cost he says will be difficult to pass on to customers, adding to pricing pressures created by lower demand as a result of Covid-19.
Like most in the processing sector he steered clear of the cheaper ethylene alternative over fears of effects on fry colours.
“There’s not been enough research yet but I’m interested to see how those who have been trialling low rates of ethylene get on.
If it doesn’t compromise the fry colour we might have a look at using low rates next year.” Another change Mr Fretwell might make is growing a larger area of varieties which appear to remain dormant for longer than other varieties, such as Markies.
“We’re also looking at reducing store temperatures a little from about 9-9.5degC down to 8degC, again without compromising fry colour, while we’re also considering installing more refrigeration in the older ambient stores so we can control the temperatures more rather than bringing in the outside air.
“You can’t imagine how many changes you need to make from losing one active.
It has had more impact than losing any other product.”
In the field Jamie Chapman, OGE Chapman and Sons, Long Sutton
Three applications of mint oil had already been applied to a small tonnage of Eurostar, one of Jamie Chapman’s three potato varieties in store at Long Sutton, by the end of January.
Like James Fretwell (see panel on p22), he also grows primarily for the fish and chip shop market and stores potatoes into June in three refrigerated box stores with a total capacity of 4,300 tonnes, all built within the last five years.
Mr Chapman says: “The initial applications went on the Eurostar at the end of November and we’re having to reapply every four to five weeks.
It is a particularly lively variety, but we have fared better with the Markies and Agria.
The Markies had their first application at the end of December and the Agria at the end of January.” The lack of residual activity has been a drawback, he says.
“Mint oil seems to have a short shelf life compared with CIPC.” Markies and Agria form the bulk of his 80 hectares of potatoes, with Eurostar only a small proportion, but this has meant some nimble store management has been required to rotate the boxes between stores to time treatments effectively, in conjunction with the other varieties.
“That’s okay on a small scale, but difficult to achieve if we had a larger tonnage of Eurostar.” Prior to going into store, maleic hydrazide (MH) was applied to the entire area as usual and, in common with other growers, he has found it has worked effectively this season.
“Potatoes are more dormant this year than normal.
The MH has worked well.” But he is concerned about years when potatoes experience more stressful conditions in summer and are more likely to sprout, or when MH does not work so well.
“In those years it will be very difficult to control and the cost implications will be painful.
“We desperately need the new chemicals, such as 1,4-dimethylnaphthalene and further down the line SmartBlock [3-decen-2-one], to be approved.
“That’s not to say mint oil doesn’t have a place, but we need more options.”