Integrating alternative sprout suppressants for the fresh market

For many decades there was significant reliance on the use of CIPC as a sprout suppressant for fresh market potatoes, even in refrigerated stores. The withdrawal of approval for CIPC (last use in 2020) required independent information on the relative efficacy of a range of alternatives for use either alone or in combination to provide sprout suppression for the fresh market sector. At the time the research was conducted, there were several alternatives to CIPC, either already on the market or un-approved, ‘near market’ options. The former included the field-applied maleic hydrazide (MH).

The project compared the comparative efficacy (+/- maleic hydrazide) of a range of sprout suppression treatments: ethylene, spearmint oil (BIOX-M), orange oil (ARGOS) and 1,4-dimethylnaphthalene (DMN) on a range of important pre-pack varieties. 

Methods

Assessment of the comparative efficacy of the sprout suppression treatments was carried out over three trial seasons. The comparison between with- and without-MH treatments was direct as the treatments were carried out in the same crops.  Four mainstream pre-packing varieties were studied: Maris Piper, Nectar, Melody  and King Edward. They were subjected to the various treatments and product combinations and assessed for sprout control over a 9 month storage period. Additionally 4 salad varieties:  Angelique, Juliette, Leontine and Maris Peer were included in the second and third years of the trial. They were assessed for their response to some of the sprout suppressants. The store temperature was 4.5ֻ°C, warmer than typical but which provided a greater sprouting pressure against which to test the various sprout control treatments. 

Results

MH treatment alone had a very pronounced effect on sprout control and subsequent shelf-life. Control was good at all residue values found in the trial with the lowest value 7.6 mg/kg providing an approx. 80 % reduction in sprout weight compared with the untreated crop. MH was effective alone for longer dormant varieties or in combination with another suppressant for shorter dormant varieties. The presence of MH with a store-applied treatment improved the overall efficacy of sprout control. After 9 months storage MH still provided effective residual sprout control during shelf-life, during which the effects of the volatile store-applied treatments dissipated.

Both spearmint oil and DMN were highly effective treatments applied in store, suitable for both short and long dormant varieties, with or without MH. Ethylene and orange oil treatments provided some control on longer dormant varieties and, in combination with MH, could provide acceptable results for pre-pack storage of some varieties.

There were no direct effects of any treatment on weight loss or on post-storage appearance of the tubers.