Maleic hydrazide is gaining a following among potato store managers to reinforce or even replace under pressure chlorpropham (CIPC) to control early dormancy break in potatoes.

Although best known as a foliar treatment for ware potatoes to control volunteers in following crops, the active can also help suppress sprouting in stored tubers.

The processing sector in particular has relied heavily on CIPC to prevent dormancy break, as tubers for crisping and chipping markets have to be stored at higher temperatures to minimise the production of reducing sugars that can adversely affect fry colour.

This makes them more prone to sprouting.

However, CIPC has been subject to significant regulatory scrutiny in recent years, resulting in the total dose coming down from 63.5g/t to 36g/t a season for processing tubers in 2017.

See also: Potato growers told to get ‘more mileage’ out of CIPC sprout suppressant

While that rate is fine for top-notch stores, it could leave tubers stored for long periods in less efficient stores, where uniform CIPC coverage is difficult to achieve, more vulnerable, says Adrian Briddon of AHDB Sutton Bridge Crop Storage Research.

He believes maleic hydrazide is most likely to find favour as an addition to CIPC, rather than replacing it.

Adrian Briddon

“There are relatively few potato storage scenarios where maleic hydrazide will succeed as a sole treatment.

“The exception might be on varieties susceptible to early dormancy break, such as King Edward,” he explains.

“I think the most likely use is where varieties with different dormancies are stored together, where CIPC is timed to protect the most susceptible varieties.

“If these susceptible varieties were sprayed with maleic hydrazide it might be possible to avoid CIPC entirely.”

Short-term storage

Maleic hydrazide may also be useful for short-term storage where CIPC cannot be used, such as those shared with other crops, or stores without active recirculation – likely to be a statutory CIPC label requirement from 2017.

It is relatively expensive compared with CIPC, but significantly cheaper than a number of alternatives, some of which are not easily suited for processing potatoes, he adds.

Some store managers are using maleic hydrazide with considerable success, says Mr Briddon.

“Efficacy is dependent on foliar uptake and translocation to the tuber, so good spray coverage will be needed on plants that are growing well.

“Applying maleic hydrazide to stressed plants increases the chance of uneven uptake as plants do not divert resource to all tubers equally.”

Cutting CIPC

Reduction in CIPC doses is driving renewed interest in maleic hydrazide use, says Frontier’s potato technical manager Reuben Morris.

He adds that growers have used it for many years to control volunteers, and it has a useful spin-off in terms of dormancy control.

“Some processing operators are only just coping at sub-36g/t levels and are worried about what could happen in a bad year.

“While we will hopefully have the new active 1,4-dimethylnaphthalene available next season, it will take time to get to know how to get the best from this. Understandably some growers are looking at maleic hydrazide with renewed interest.”

While there is plenty of literature on what results growers can expect from older varieties, however, little or no work has been carried on newer ones, he points out.

“It can work well on some varieties and not on others – really the only way to find out is by experience, or asking someone else who may have the answer.”

Yield penalty

Some growers are concerned about a potential yield penalty, he adds, but suspects those that stick closely to label advice are achieving the best results, avoiding times when crops are stressed.

“They should use plenty of water to get the active into the crop to ensure all tubers get as even a dose as possible.”

Maleic hydrazide is systemic, so residue can be found within the tuber, rather than on or near the surface as with CIPC, which can be removed by peeling.

However, its use is now widely accepted by processor end-users and by supermarkets for pre-packs, Mr Morris adds.

“Use drifted away when supermarkets introduced tighter protocols on residues, but they have since relaxed their stance.”

Spot-on application crucial

© Tim Scrivener

Growers must assess the suitability of maleic hydrazide on a case-by-case basis, says Don Pendergrast, product development manager for Arysta, the approval holder for maleic hydrazide product Fazor.

“You can expect four months of good control, but this will vary according to variety and store conditions.

“To optimise efficacy, correct application is key and must be carried out in accordance with the product label.”

The product should be applied to healthy foliage at 5kg/ha in 350-500 litres/ha of water as a medium-quality spray, says Mr Pendergrast.

“Spraying should not take place in temperatures exceeding 25C when plants are likely to be stressed, or during periods of drought.”

Correct timing is vital, he adds. “The product should be applied when marketable tubers are 25mm in diameter – when cell division is complete. This is typically three to five weeks before harvest.

“If application is too late the active ingredient will not translocate in the required concentrations to developing tubers and efficacy will be reduced.”

Although more expensive than CIPC, he reports increased interest from growers looking to augment CIPC or avoid it altogether due to application problems and consequential maximum residue level exceedances, or to end-user pressure.

“Fazor can be incorporated into the blight programme, which helps to offset the extra cost,” says Mr Pendergrast.

“No specialist equipment or additional operation is required and growers also get additional volunteer control and protection from secondary growth.”