Determining the efficacy of Agrigold as a post-harvest treatment to improve shelf life of potato
Dr Mieke Daneel
ARC-Institute for Tropical and Subtropical Crops,
Private Bag X11208, Nelspruit 1200
February 2012
BlueGold Water and Chemicals
Fairland
2195
AIM
To conduct a trial in the potato pack house at SIS Farming, Bethal, Mpumalanga Province, to determine the efficacy of Agrigold as a post-harvest treatment for the improvement of shelf life in potato.
INTRODUCTION
In a pack store, water is an essential part of the pack line as the potato needs to be cleaned of soil, debris, bacteria and spores brought in from the field. Often water used is untreated implicating that bacteria are present. However, even when water used is treated, the amount of potatoes packed during the day and the amount of soil and organic material on the potato and harvesting equipment have a direct influence on the water quality resulting in poorer quality of potatoes packed and a shortened shelf life. Therefore it is necessary to use a sanitizing agent in the water. This agent must kill bacteria building up in the water and will prolong the usage of the water and ensure a better shelf life of the vegetables packed. Agrigold is such a sanitizing agent.
EXPERIMENTAL PROTOCOL
The trial was executed on the 14th of December 2011 at SIS Farming, Bethal, Mpumalanga Province.
Replicates: 6
TREATMENTS AND DOSAGE RATES
Table 1 Treatments, dosages and pH (water) for the different treatments
| Treatments | Agrigold dosage | Sporekill | pH |
| 1 | – | – | – |
| 2 | 1/5000 | – | 6.86 |
| 3 | 1/2500 | – | 6.70 |
| 4 | – | 1.5 l/2000 l water | 7.05 |
*Sporekill is the standard sanitizing agent used in the potato pack line; water temperatures was 19.4oC; Treatment 1 was not put through the pack line
Application rates
Agrigold®
| Treatment no | Application rate |
| 2 | 20 ml/100l water |
| 3 | 40 ml/100l water |
Sporekill®
| Treatment no | Application rate |
| 4 | 75 ml/100 l water |
Test substances
Formulation Trade Name: Agrigold®
Active ingredient: Copper (<6%)
AI content: 52.87 g/l
Formulation type: Soluble liquid
Supplier: Blue Gold Water and Chemicals Pty (Ltd)
Registration number:
Batch number: 10811
Manufacturing date: 10 August 2011
Expiry date: 10 August 2016
Formulation Trade Name: Sporekill®
Active ingredient: dimethyl didecyl ammonium chloride
AI Content: 120 g/l
Formulation Type: SL
Supplier: ICA International Chemicals Pty (Ltd)
Registration number: L 7115
EXPERIMENTAL DESIGN
Complete randomised design
LOCATION
The trial was conducted in the pack house of SIS Farming, Bethal, Mpumalanga Province.
TEST SYSTEM
The test system was a potato cultivar ‘Mondial’.
TIME PERIOD
The trial was started on the 14th of December 2011 and continued until the 10th of February 2012.
Applications were done once as a post-harvest treatment in the pack store.
APPLICATION METHOD
The product was dissolved in a water bath and potatoes were sprayed with this water as usual in the potato pack store. The potatoes move through this washing/spraying system for about 2 minutes. Thereafter potatoes are dried, sorted and packed. Treated potatoes were taken and put into bags. Treatment 1 received no treatment in the pack store. Potatoes were taken from the bins before entering the pack store and were packed in bags.
Potatoes were taken to the ARC-ITSC for evaluation. Potatoes were kept at room temperature at 25oC in paper bags for regular evaluations. Twenty five potatoes per bag replicated six times were evaluated.
ASSESSMENT
- Phytotoxicity of the treatments
- Determining number of rotting fruit
ASSESSMENT PERIOD
From 15th of December until the 10th of February.
DATA INFORMATION
Phytotoxicity
No phytotoxicity was observed in any of the treatments with single (1/5000) or double dosage (1/2500) of Agrigold.
Rotting of potatoes
Table 2 shows the development of rotting (i.e. Erwinia) for the different treatments from 15th of December until the 10th of February 2012. The potatoes were of good quality and took more than 4 weeks before any rotting was observed except for two potatoes that were probably rotten before the trial started. From than onwards (week 5) the rotting was significantly different for the UTC compared to the other treatments as can be seen in Table 2.
From week 5, rotting was observed in the other treatments but always at a much lower rate. At week 9, 65 out of 150 potatoes were rotten in the UTC compared to 45/150 in Sporekill, 37/150 in Agrigold 1x and 14/150 Agrigold 2x.
The incidence of Erwinia was significantly lower in the Agrigold treatments than in the untreated control from week 5 until termination of the trial in week 9. The 1/2500 dosage did seem to perform considerably better than the 1/5000 dosage especially at week 8 and 9.
Both treatments showed less rotting than the Sporekill treatment which is the standard method. The 1/2500 dosage differed significantly from the standard method at week 8 and 9.
Table 2 Percentage potatoes developing Erwinia after post-harvest treatment for the different treatments over time
| Week 2-4 | Week 5 | Week 6 | Week 7 | Week 8 | Week9 | |
| Untreated Control | 0 a | 6 a | 10.7 a | 10.7 a | 30.0 a | 43.3 a |
| AG 1x | 0.7 a | 0.7 b | 1.3 b | 2.7 b | 18.6 ab | 24.7 bc |
| AG 2x | 0 a | 0 b | 0.7 b | 1.3 b | 6.0 b | 9.3 c |
| Sporekill | 0.7 a | 0.7 b | 3.3 b | 3.3 b | 25.3 a | 30.0 ab |
| F pr | – | 0.003 | 0.002 | 0.007 | 0.023 | 0.003 |
| Lsd | – | 3.261 | 5.091 | 5.368 | 15.45 | 16.07 |
| CV% | – | 147.7 | 105.7 | 99.0 | 64.1 | 49.7 |
Means within a column followed by the same letter are not different (P< 0.05) according to Fisher’s Protected Least Significant Difference test
DISCUSSION AND RECOMMENDATION
Agrigold is a sanitizing agent that is effective in enhancing shelf life of potato against the recommended dosage of 1/5000. Shelf life was extended in comparison with the untreated control and the standard method (Sporekill).
It might however be considered in the potato industry to use the 1/2500 dosage as the standard dosage because of the significantly better results with this dosage.
No phytotoxicity was observed in any of the treatments with Agrigold.