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.