Integrating alternative sprout suppressants for the processing market

Effective sprout control is critical to the year-round supply of ware potatoes and the industry had largely become reliant on chlorpropham (CIPC) for this. In official figures from 2016, CIPC accounted for 82% of treatments to stored potatoes, while ethylene and spearmint oil accounted for 15% and 3%, respectively. The potato processing industry especially is dependent on the availability of growth regulators because storage at lower temperature (c. 3-6°C) cannot be used because of its effect on processing quality.

The aim of this project was to investigate whether sprout suppressants other than CIPC could provide effective sprout control. Products containing one of the three registered active substances (ethylene, maleic hydrazide and spearmint oil) were studied. They are generally considered less effective than CIPC, may have adverse effects on other qualities of the stored crop and, in all cases, are more costly. However, due to changes in pesticide approvals, the last use of CIPC as a sprout suppressant was in 2020, and as a result alternative options needed to be adopted. In addition to the three UK registered alternative sprout suppressants, application of 1,4-dimethylnaphthalene (marketed as 1,4-SIGHT) was also assessed. At the time this was available in several EU member states, but has not received full registration in the UK. Application of 3-decen-2-one was also assessed. It is marketed as SmartBlock® in the USA and other countries.

This study focussed on the assessment of potatoes stored for processing, a similar study was carried out for potatoes stored for the fresh-pack market.

Results 2019-2020

• Pre-treatment with MH resulted in satisfactory (≤10mm) control of sprouting in samples by all post-harvest applied sprout suppressants after long-term storage at 9^oC
• In MH-treated samples, sprout control was very good following use of DMN and SmartBlock®
• Post-harvest treatment with ethylene or spearmint oil (Biox-M) & ethylene was not associated with deterioration in processing quality
• Long store closure periods, following chemical applications, in combination with high store carbon dioxide levels (1%) did not give rise to darker fry colour compared with a standard 48 hour closure period and control at 0.3% carbon dioxide

Results 2020-2021

• In samples treated with MH, residue levels were higher in 2020-21 than in 2019-20 (average of all cultivars approx. 23ppm in 2020-21, compared with approx. 11ppm in 2019-20)
• In MH-treated samples good sprout control (<5mm) was achieved by all post-harvest treatments after long-term storage at 9^oC
• Sprout control was virtually complete following use of DMN and SmartBlock® in MH-treated samples
• In MH-untreated samples good sprout control (<5mm) was only achieved using DMN
• DMN resulted in good sprout control irrespective of cultivar and MH pre-treatment
• None of the sprout suppressants affected fry colour
• Processing quality following treatment with ethylene was the same as other post-harvest treatments
• Allowing store carbon dioxide concentration to achieve 1%, compared with a conventionally managed store where concentration was managed to not exceed 0.3%, did not give rise to differences in processing quality

11140061 Spearmint oil efficacy trial on crisping varieties

The report from a separate trial (2019-2020) is also provided. The work was conducted in collaboration with the Potato Processors’ Association and was carried out to evaluate the relative performance of crisping stocks when treated with spearmint oil.

At intake, crops were generally of acceptable quality. However, by sampling occasion 1, after 15 weeks’ storage, sprout control varied widely. Fry colour was generally good but there were several varieties with poor defect levels.

At the second sampling occasion, after almost seven months’ storage, only five varieties had adequate sprout control (longest sprout <10mm). These were Verdi, Markies, Taurus, Lorimer and VR808; only the latter was controlled without MH. The spearmint oil and MH combination worked well as a sprout control combination. However, fry defects were only below a 5% threshold in two of the 12 stocks. This may have been a consequence of the sprout control treatments, but the relatively late loading date and the use of a single storage temperature may also have been factors.