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How to get the best out of maleic hydrazide

With chlorpropham (CIPC) no longer available for use in potato stores, many will look to foliar applied maleic hydrazide (MH) for early insurance against sprouting. Potato Review gets some expert advice on how to maximise its efficacy.

two processes inspect store potatoes
Fokke Smit, Certis NL

The potato industry will soon be embarking on its first storage season without CIPC, which has been the go-to means of sprout suppression in store for decades.

One of CIPC’s advantages was its low volatility. Once applied as a hot fog, it settled on tubers and persisted for a considerable time before reapplication was required.

This was the case even where stores were regularly ventilated with ambient air, either for cooling or flushing out CO2.

Now it is no longer available, there are just two approved options for use in the UK: spearmint oil product Biox-M and ethylene gas.

There is also hope that DormFresh’s dimethylnaphalene (DMN) product 1,4Sight will be authorised in time for the 2020 storage season.

AHDB’s Sutton Bridge Crop Storage Research sprout suppression expert Adrian Briddon says that while these substances undoubtably have a role to play in sprout control, they are all eminently volatile.

“That means whenever we ventilate with ambient air, we are extracting the chemical or storage treatment from the store and hastening the need for reapplication.

“This will have implications for storage costs and untended, could have implications for sprout control efficacy, too.”

Key role

Work carried out at Sutton Bridge suggests that MH has a key role to play in dealing with the potential issues of compromised efficacy and increased cost of these volatile compounds in the early stages of storage.

But growers must get the application of MH just right if they are to reap the full range of benefits it offers including more cost-effective sprout suppression in store.

The foliar applied plant growth regulator – which is applied to a growing crop ahead of desiccation – is absorbed by the crop canopy and moves into the tubers.

Mr Briddon has been conducting trials for the past two years looking at MH use followed by a range of in-store treatments – Biox-M, ethylene, DMN and CIPC as the benchmark – on five varieties.

“We’ve seen that maleic hydrazide is a reasonable sprout suppressant in its own right and it can certainly give sprout control for a matter of months, but more importantly than that, it delays or reduces the need for other treatments,” explains Mr Briddon.

A dose of MH costs less than £2/t which is just 80 pence more than CIPC (see Sprout control product costs).

Any reduction in the use of the more costly alternatives will help to keep the cost of storage under control.

Volunteer control

There are other benefits from MH including volunteer control. Certis trials in the Netherlands suggest an average of 70-90% of treated tubers left behind after harvest are unviable.

With volunteers propagating soil borne diseases, late blight, virus and potato cyst nematode (PCN), this will assist IPM around the rotation.

MH also reduces secondary growth, is the only treatment to control internal sprouting – where a sprout turns inwards beneath the eye and grows through the inside of the tuber – and limits chain tuberisation.

The latter can reduce dry matter content in tuber samples and MH negates this.

Mr Briddon says there is a concern that users may not be fully reaping the sprout control benefits of MH, as he sees some variability in efficacy and sees application timing as the biggest factor.

There is a risk of a yield penalty when the product is applied too early, but Mr Briddon feels this has been overstated, resulting in some growers applying too late and compromising uptake into tubers.

Difficult job

“However, it has to be acknowledged that unlike treating potatoes in store, where conditions are fairly constant, out in the field there are many variables which makes it much more difficult to get right.”

Simon Alexander, an independent potato specialist advising across East Anglia, believes many growers won’t miss the opportunity to use MH this season and get some peace of mind that dormancy break will be delayed once crops go into store.

Like Mr Briddon his experience of MH has been variable with some crops showing little response and others still dormant the following April.

“I think that’s largely down to application timing and conditions and my concern is that there hasn’t been a significant amount of UK research into MH use in recent years.

“But with an increased focus on the importance of MH now CIPC has gone, I think our application will improve and that variability should reduce. We should get what we need out of the product,” he adds.

Application is king

While there haven’t been extensive MH trials carried out in the UK, Crown MH marketing company Certis Europe’s technical specialist Fokke Smit has been working with the active in the Netherlands since 2010.

He estimates 60 to 70 per cent of Dutch growers use it each season and this is only set to increase as they are forced to live without CIPC.

In his experience, application timing is the overriding success factor because of the way the active works. It must be applied to a fully functioning plant and given time to be taken up by the leaves and translocated to the tubers.

This means that a plant must not be suffering stress from heat, drought or disease and the product must be applied long before the planned date of desiccation to optimise uptake into the tubers.

“You should apply between three and five weeks before desiccation, with the optimum being five weeks,” advises Mr Smit.

Independent potato consultant Martyn Cox agrees that timing trumps all other factors in getting the most out of MH and emphasises that conditions at application must be within the recommended environmental parameters.

Relative humidity

With uptake intrinsically linked to relative humidity, he says making sure the product is sprayed when RH is above 75% and not likely to fall for a considerable period afterwards is critical to avoid compromising uptake.

It should also be applied below 25C when no rain is forecast, or irrigation scheduled for at least 24 hours after spraying.

“On warm and dry days, it will be better to spray in the evening when its cooled and ahead of the dew point.

“If you have to wait a bit longer for the correct conditions, that’s the right thing to do, as uptake is the most important factor for efficacy. Don’t blindly stick to the five-week limit.”

Mr Smit says in a normal season hitting the three to five-week pre-desiccation window should be achievable and also advises using higher water volumes with a slow forward speed.

“Where you use less water and travel too fast, deposition is poor, and the solution dries too fast on the leaf and hinders uptake. In trials we see 250-litres/ha as the minimum, but we recommend 300 – 500 L/ha where possible, particularly if the weather is warm and dry.”

Balancing act

Growers should be well-drilled in planning desiccation timing and some will even have a date in mind before planting.

Mr Cox says in these situations, counting back 35 days from the planned desiccation date provides a reasonable guide to MH timing.

However, where it becomes more of a balancing act is on varieties that are highly determinate, such as Innovator.

They can senesce very quickly, particularly on a site with low nutrient status or where the crop is stressed by heat, drought or diseases such as Alternaria spp.

Determinate varieties should be prioritised for inspection about six weeks from the expected burn off date and MH applied when conditions are optimal. Otherwise, growers may get caught out as MH cannot be applied to a senescing crop.

“For indeterminate varieties that go on forever, like Cara or Markies, you cannot be complacent, but you have more breathing space.

“Once flowers have dropped off – if the variety does flower – and you have the majority of tubers close to the desired size fraction (80% greater than 25mm), then you can think about spraying at the next opportunity,” explains Mr Cox.

Standalone product

Blight fungicides can contain adjuvants that help the product stick to the leaf and dry faster but this is counterproductive to maleic hydrazide uptake so it should be applied alone.

“I’m often asked if you can add an adjuvant or sticker to maleic hydrazide in case of rain, but my advice is to only use MH on a day when rain is not expected.

“You should be able to find one in the 2-3-week window and why add the extra cost?” explains Mr Smit.

Ths is backed by Mr Alexander, who adds: “Growers have been thinking about how MH applications fit around blight spraying and irrigation, but I think its increased importance without CIPC will require us to fit the irrigation and blight spray around the MH in order to get the most out of it,” he adds.

Secondary growth

A final consideration for application timing is secondary growth which occurs when crops are stressed.

As temperatures cool and water arrives either through irrigation or rainfall, the crop starts putting energy into producing haulm rather than tubers which can dent yield and reduce dry matter content.

Such conditions can also cause secondary growth below ground, manifested in chain tuberisation.

Mr Smit says there is little growers can do if secondary growth occurs around June, but if it occurs in July an application of MH can help to stop it, but timing is again critical.

“Where applied just one day after a stress period, good results are not always achieved. It’s best to spray two or three days after and it can do a fantastic job of stopping secondary regrowth.”

“In these situations, where rapid regrowth is occurring, a phytotoxic effect is sometimes seen after MH application.

“However, this is not negative phytotoxicity, it is a positive, because it means the product is doing its job. Under normal conditions, you will not see any effect in the crop”

Additional benefit

Mr Smit adds that Certis’ work in the Netherlands has shown MH treatments to significantly reduce weight loss in store.

It could be argued this was irrelevant when growers could still use CIPC. However, in its absence where stores are old and not in the best condition to utilise volatile alternatives, MH can provide a means of slowing any weight loss that may occur.

“When you apply MH, you should get less respiration in store and less water loss and that means more tonnes sold.”

Sprout control costs

Sprout suppressant regime

Sprout suppressant cost (£/t)

Packing (refrigerated @3.5C)

 

CIPC (1 dose)

1.20

Maleic hydrazide

2.00

Spearmint oil (1 dose)

4.50

Ethylene

3.50

Processing (ambient @9C)

 

CIPC (3 doses)

3.60

Maleic hydrazide + spearmint oil (3 doses)

15.50

Maleic hydrazide + ethylene

5.50

Maleic hydrazide + DMN (2 doses)

11.00

(Source: AHDB Potatoes. Based on 8-month storage period)

Getting the most out of maleic hydrazide – key points

  • Maleic hydrazide can play a key role in sprout control programmes and reduce overall storage costs, according to AHDB research
  • Other benefits include reduced secondary growth and volunteer potato control
  • Application timing and quality key in maximising performance

Dos

  • Apply to second early and maincrop potato varieties
  • Treat healthy and actively growing crops
  • Apply 3-5 weeks before desiccation
  • Spray on a cool day (<25C) when RH is >50% and no rain forecast for 24 hours
  • Use a higher water volume – 300-500-litres/ha recommended
  • Reduce forward speed of sprayer to 8-12kph

Don’ts

  • Apply too early (more than five weeks before desiccation risks yield penalty)
  • Apply too late (within 3 weeks of haulm destruction)
  • Apply after the onset of senescence
  • Treat crops showing signs of stress (water/disease/nutrient)
  • Spray in hot or dry conditions
  • Use with blight sprays or adjuvants