When your potato crop emerges, you will need to ridge it – that is, cover the tubers with a raised strip of soil. The timing of this is very important. Potato plants must be ridged just as the tubers develop from above the root system. If the tubers are not covered, they will turn green and be vulnerable to insect attack. If you ridge in time, either with a tractor or a hand hoe, you will also kill young weeds between the rows and cover those in the row. Don’t delay; the weeds will soon grow large and strong enough to recover after rain or irrigation.
If you are using a tractor, be careful not to cover the potatoes completely. For the first ridging, use just enough soil to control the weeds. Later, you can move more soil up onto the ridge. Once you have ridged the crop, rainwater will flow down the sides and into the furrow. Be warned: the soil in the ridge dries out fairly quickly, even after a good shower. The ridge may appear to be thoroughly wet, but if you dig into it, you may be surprised at how dry it is.
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There are two reasons for this. Firstly, overwatering will see most of the water settling between the rows. Secondly, the concentrated root system in the ridge will dry out the soil in this area when there are many leaves on the plant. This is different to other crops and most important to understand. To keep the soil in the root zone moist, irrigate frequently and lightly. Any water stress will greatly reduce the size of the tubers and the yield as well as increasing the chances of scab.
Maintaining nitrogen levels
Make sure that the nitrogen level is kept sufficiently high until the tubers have sized up. Check the colour of the leaves; they should always be the same dark, lush green as when they were young. To achieve this, apply at least one side-dressing of LAN.
Pests to watch out for are aphids, caterpillars and potato ladybirds, which eat the leaves. Apart from stressing the crop, aphids can spread viruses. Caterpillars should only be sprayed if their numbers are very high. A few here and there will not present problems. Potato ladybirds, on the other hand, can cause tremendous damage. They usually appear suddenly after the first summer rains and do damage before they are noticed. Fortunately, several insecticides are available to control them.
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Harvesting and planning ahead
The tubers are ready to harvest when the plants start to yellow and die back. Make sure that the skins are firm before lifting the tubers. If the crop was healthy and virus-free, you can keep the smaller-size potatoes for the next planting.
- Potatoes were first cultivated in Peru and Bolivia in South America in about 6 000BC. Spanish explorers introduced the potato to Europe in the second half of the 16th century.
- The word potato comes from the Spanish name for the tuber – patata. This itself is a joining together of two South American names – batata (sweet potato) and papa (potato). For a long time ‘potato’ referred solely to a type of sweet potato.
- About 5 000 potato varieties are grown around the world. According to the UN, the top three producers of potatoes are China (88 million tons), India (42 million tons) and Russia (32 million tons).