The objective of the harvesting operation is to lift the crop with the minimum of damage to the tubers prior to storage, and with the minimum amount of clay, dirt, stones etc.
The first stage in harvesting potatoes is to desiccate or “burn-off” the foliage (haulms). This is particularly important in crops for storage. In the case of crops which are being graded and sold immediately it is less critical. Crops lifted with immature or blighted foliage carry a high risk of rotting in storage.
Potato foliage and stalks need to be removed before harvesting to prevent blight infection of the tubers and to facilitate the passage of the harvester. Burning off also removes any weeds which would interfere with the working of the harvester.
Desiccation is the application of a special agrochemical designed to kill off the green foliage. The desiccant should be applied when the tubers have reached the desired size. Dig up tubers in different locations in the field to assess their size and make a decision. Allow a period of two to three weeks from the time of application of the desiccant to the start of harvesting.
This allows the tuber skins to mature and therefore be less prone to damage and disease at harvest time and in the store. Aim to harvest crops by mid - October, so that the operation can take place in relatively warm (7oc or greater) soils. Harvesting potatoes in cold wet soils will initially lead to a greater number of diseased and rotten tubers.
There are a range of chemical products on the market available for use as desiccants. A number of the most popular products are based on the chemical Diquat, which works by contact and has limited translocation in the plant.
Warning: Haulm desiccants can damage tubers if applied during or shortly after dry periods. A “dry period” definition varies with soil and crop type, so read the product label carefully before use. Some varieties may also be susceptible to a particular chemical.
Lifting and Harvesting
Healthy potatoes in the soil at harvest time are in perfect condition.
Damage to the tubers is caused by:
- Late harvesting in November and December
- Wide tyres encroaching on the ridges resulting in bruised and damaged tubers and the creation of clods.
- Setting of the digging share either below or above the bed of tubers and excessive agitation of the webs of the harvester.
- Worn and sharp edges on machinery parts.
- Allowing potatoes to drop in height in excess of 20cm, thereby causing damage.
As much as 20% of tubers are damaged at harvest time. So it pays to follow the correct procedure to ensure losses are kept to a minimum.