Why growers need to use sprout suppressant early this season
A combination of the high summer temperatures and growers being unable to apply maleic hydrazide means potatoes coming into stores this season will be under increased sprouting pressure.
That’s why growers are being advised to act early and treat crops with a new sprout suppressant.
And for the first time this season, they can take advantage of 1,4SIGHT (1,4-Dimethylnaphthalene or DMN), since its recent approval by the Chemicals Regulation Division of the Health and Safety Executive.
See also: Are no-till potatoes a pipe-dream?
DMN is a proven product with commercial use beginning in the US as early as 1996. It is now being used in other countries, including some in Europe, and users have reported good efficacy.
High-pressure season
The product arrives in what experts predict will be a high sprouting pressure season and say early treatment may be key.
Adrian Cunnington, an independent storage consultant at Potato Storage Insight, highlights that there have been reports of sprouting in the field. This early dormancy break is due to the accumulation of heat.
Ajay Jina, technical manager at DormFresh, which developed DMN, adds that this summer’s extreme conditions also meant many maleic hydrazide applications didn’t go on crops.
Maleic hydrazide is a growth regulator that can give residual background suppression of sprouting, similar to CIPC.
MH is ideally applied three-to-five weeks prior to haulm destruction – and back then, temperatures were too high. For example, Fazor or Crown MH, should have been applied when temperatures were below 25C.
In addition, it is applied when 80% of tubers are 20mm or greater, but many crops were not at that size, so didn’t receive it.
Therefore, both experts agree that, with less residual control, sprout management could be tricky this storage season and early treatment will be key when using DMN.
In active potatoes, Mr Jina says growers should aim to apply DMN as soon as potatoes have dried and cured.
They need to be dry to absorb the product through the skin and good uptake is essential in having high enough concentration in tubers to work efficiently.”
He explains that leaving it later could see growers having to apply more and at shorter intervals to manage sprouting, especially in high pressure situations.
He recommends:
- First application: early, even for crops that have received maleic hydrazide
- Second application: at first signs of fresh sprouting.
Mr Cunnington adds that if growers get DMN on early enough, it should do the job well.
DMN use – key questions answered
The arrival of 1,4-Dimethylnaphthalene or DMN means growers have a choice of four post-harvest sprout suppressants this season.
These are:
- Ethylene
- Mint oil
- Orange Oil
- DMN
What is DMN and how does it work?
Independent storage expert Adrian Cunnington says that the first thing growers need to consider is that DMN, like the others, is not CIPC.
CIPC was unique with an unusual mode of action. It stopped cell division and was applied as a true fog (a suspension). The particles on a potato acted as a reservoir that volatilised over time, so kept topping up levels in any sprouts, giving what that all-important “residual control”.
In contrast, DMN is a dormancy enhancer. It is a compound naturally present in potatoes. It was first worked on in the 1980s by Harry Duncan of the University of Glasgow.
The compound being sold by DormFresh is a synthetically identical version of the natural compound.
How do you get hold of it?
DMN is applied as a hot fog into stores and for this year, DormFresh’s Ajay Jina says it is available through contractors.
Mr Jina says that it may become more widely available in subsequent years and some major growers are showing interest in applying the product.
What is the typical dose?
While the label specifies a maximum of six, 20ml applications, experience in Europe is that growers don’t need that much, says Mr Jina.
Although it can vary depending on season, whether it’s for fresh or processing markets, the type of store and so on, DormFresh is finding that growers typically need 60ml/t in three to four applications.
However, the company points out that optimisation of storage practices and matching application doses to crop requirements have allowed users to reduce rates to as little as 30ml/t for long term storage (more than seven months).
Is there a residue limit?
DMN is subject to a maximum residue limit of 15mg/kg (15ppm). And there is a 30-day harvest interval, which means growers have less flexibility when unloading stores.
Mr Jina says that DormFresh is working to get this brought down by supplying additional data to the authorities.
Until then, Mr Cunnington says if things don’t go to plan, such as delays at the factory, or if sprouting pressure is high close to unloading, growers may have to go with one of the alternatives with a shorter harvest interval.
Both mint oil and orange oil are suitable for this. For example, orange oil only has a 48-hour period.
What about air management?
Some use of fans is needed to provide circulation of the product, and stores must be closed for 24 to 48 hours after fogging to allow uptake by the potatoes.
Mr Jina adds that DMN is very volatile, so distributes throughout the store very well. However, having good airflow in store helps ensure maximum efficiency.
Mr Cunnington says applying sprout suppressants is relatively easy with bulk stores, as the air has to go through potatoes, but there is a need to avoid condensation problems. In a wet season, growers would need to remove loose soil.
Box stores are more tricky as they tend to have poorer air circulation systems. They may need to be managed carefully to avoid problems such as short circuiting and cold spots, which leads to poor chemical distribution, says Mr Cunnington.
How much does it cost?
Cost wise, Mr Cunnington says DMN is expected to be somewhere between mint and orange oil which are about £4.50/t and £3/t, respectively.
How did DMN perform in Sutton Bridge crop storage research trials?
Mr Cunnington, who managed the research, recalls trials comparing CIPC with alternatives including orange oil, mint oil, ethylene, and DMN (see graphs).
“Overall, it gave the best response in trials at Sutton Bridge, including warmer temperature processing potato stores, where sprout suppressants are used the most.”
Finally, what about Northern Ireland?
DMN is only approved for Great Britain, so Northern Irish potato growers can’t use it says Mr Jina. An emergency authorisation is being applied for and may be granted later this year.
How breeding could help in the longer term
Independent potato storage expert Adrian Cunnington believes the days of storing potatoes above 10C are gone.
CIPC was used to successfully store potatoes at 11 or 12C, says Mr Cunnington. But sprouting pressure is highest at these higher temperatures, resulting in a greater reliance on chemical control.
He believes there is a need for more processing varieties that can be stored at lower temperatures.
“At colder temperatures, you can get more sugars which leads to brown crisps.” But some varieties are less susceptible to this browning.
For example, crisping variety Claire can be stored cool, but Taurus has to be stored warm to get the required quality.
“We should be aiming more towards modest temperatures like sixes and sevens for longer storage.
He says growers would still need to use sprout suppressants at these cooler temperatures, but fewer applications would be needed.
Therefore, breeders have a role in bringing varieties to the market that can be stored cooler and acceptable for eating quality.
