Archive for the ‘Potato’ Category

Potatoes: Seeds and storage cause problems

Wednesday, September 12th, 2012



Seed potatoes in a Diffused Light Store (DLS) (above). The more the sprouts in a potato seed tuber (below), the higher the yield.

Potato farmers could earn good income if they had good seed and proper storage facilities in their farms.


Potatoes play an important role in Kenya’s food security; they might even become more important with regard of the devastating maize disease. It is hard to understand why the potato industry has been neglected for a long time. The sector experiences two mayor challenges: Lack of good seed and poor storage facilities.


More certified seed needed




Lack of certified seed has forced farmers to recycle seed planted the previous season, spreading diseases such as bacterial wilt and other viral infections.  More than 95.6 per cent of all potato seed planted by farmers in Kenya are transferred from the previous season.  Out of the 60,000 metric tonnes of certified seed required to meet the country’s demand, research institutions and certified seed producers can only produce 2,640 metric tonnes of quality seed. It is therefore very difficult for farmers in most parts of the country to get good quality seed for planting. What makes the problem worse: Although 90 per cent of farmers store their own seed, only four per cent of them have received training on seed storage.


Poor sprouting causes poor growth




What farmers are forced to do in most cases is that at the time of planting, they use the available potatoes in their seed store, regardless of whether they are well-sprouted or not. Such poor potatoes will only produce one or two stems, which lead to poor yields. Moreover, climate change has led to reduced rains in most potato growing areas. It is only well-sprouted potato seeds that can do well in reduced rainfall amounts.


Lack of knowledge on the benefit of well-sprouted seed on potato productivity has led to poor potato yields on many farms.  But this will change soon.  A training programme has been launched where farmers will be trained on how to build suitable stores for potato seed storage on their own farms.


How to store potato seed




Farmers in the project areas are taught selection of seed, and how to prolong their storage period such that they have well-sprouted seed potatoes within 8-9 months, that means until the time of planting. For example, when the potatoes are harvested in January or February, they should have sprouted well for planting by September the same year if stored under the right conditions.


Farmers can benefit from increased yields if they can practice the following tips for seed storage:

• Two weeks before harvest, cut off the stems at the base; this allows the potatoes to harden and reduce moisture loss.

• Sort potatoes immediately after harvest. Only potatoes the size of a chicken egg or smaller are suitable for seed.

• Remove all bruised potatoes to prevent entry of disease causing agents and rotting. Do not wash potatoes meant for seed; the water may be contaminated.

• Do not store potatoes in direct light; they turn green and cannot be used as seed or even for consumption.

• Place the potatoes in a raised platform or a dry floor. The store should be rat-proofed.

• Do not use synthetic bags for potato storage; sisal bags are ideal as they allow air circulation. Alternatively, store them in net bags, which allow light and ventilation.

• Storage stores should face the East-West direction; this reduces the amount of light getting into the store (Diffused Light Stores).

• If using an ordinary store, cover your seed potatoes with grass to help them sprout and prevent the amount of light getting into the potatoes.

• Good seed potatoes should be well sprouted; there should be a uniform sprout in all eyes.

• Potato sprouts should be at least 2 cm in length before planting.


Storage is the big problem




Potatoes are perishable; this makes it very difficult for farmers to store them for a long time after they are harvested.  They have to be marketed immediately.  If the market is flooded with the commodity, prices go down, exposing farmers to losses. In the developed countries, potatoes are stored in huge silos with refrigeration. The lack of this infrastructure in the developing world forces small-scale farmers to use other methods.


In any way, after being dug out, the tubers should be well dried. Make sure your potatoes are not exposed to sun, rain or wind. By the end of two weeks, they’ll have thickened skins and any nicks will have healed. All damaged tubers should be rejected and the sound, healthy ones can then be kept in the store.


Whether the potatoes are placed in bins, bags or boxes, the main consideration is air circulation.  For this reason, a slatted box is usually best. The storage atmosphere should be well moistened (90 per cent relative humidity).  Exposure to light hastens sprouting and produces a green colour or sunburn; hence potatoes should be covered or shaded from light. As the storage season advances, potatoes should be examined from time to time and when sprouting is evident, remove the sprouts and reject the damaged or diseased tubers.


Using sawdust



Githenya Kariuki prepares potatoes for storage using saw dust.

Some farmers in potato-growing areas have discovered how to preserve potatoes using sawdust. The potatoes are sorted for storage by removing the bruised, those with tuber moth holes and the rotting ones. The farmers then spread a thick layer of dry sawdust across the clean floor of the store.  They then spread the potatoes on the sawdust and add another top layer of sawdust to cover the potatoes. Githenya Kariuki, a farmer in Kinungi area in Naivasha has used this method for the last five years.  He says that he has managed to extend the shelf-life of his commercial potatoes for up to 5 months without any sign of damage. This method may benefit farmers to store their surplus potatoes until the market prices are favourable.  It also helps improve the household food security because the farmers can store potatoes all year round for home consumption or even sprout them for replanting.


Storage and marketing projects started


The twin problem of potato storage, both for seed and market may come to an end if two projects started recently prove successful. In the first project, farmers will be trained on proper selection and storage of seed on their farms.  The National Council for Science and Technology is funding the three-year pilot through Mount Kenya University in collaboration with KARI and the Ministry of Agriculture. Already seven farmers from seven districts in potato growing areas have been trained on on-farm potato seed storage under the project.


To stop exploitation by middlemen and improve potato marketing, a programme, Small Holder Marketing Project (SHOMAP) wwill help farmers deliver their potatoes to collection centres. Potato processors, supermarkets, hotels and other buyers will buy potatoes from these centres at the prevailing market prices.


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Bacterial wilt a big threat to potato growing

Monday, May 28th, 2012


Adoption of crop rotation is the main solution in the fight against the destructive potato disease.


Although it continues to destroy potatoes countrywide, very many farmers are yet to understand what bacterial wilt is, how it is spread and how to control it. Most farmers have stopped growing potatoes altogether because their soils are already contaminated.  Farmers are opening up new fields in an attempt to control the disease but only end up spreading it further because the seeds they use are already infected. The best way to stop bacterial wilt in your shamba is to know what it is, how it is spread and how to control it.


Causes of the disease

A potato plant infected by bacterial wilt


Bacterial wilt is caused by a bacterium called Ralstonia solanacearum. The disease is mainly spread in two ways: When infected seed is planted in healthy soil or when clean seed is planted on soil that is already infected. The major source of seed for many Kenyan farmers is usually seed that was planted the previous season. If the potatoes are infected, they spread the disease.


Other farmers buy potato seed from their neighbours; if the seeds are infected, the disease is introduced into their farms. The disease can also spread if infected crop residue is transferred into an area with healthy soil. If contaminated water from surface run-off flows into an uninfected farm, it can spread the disease. The water used for irrigation can also introduce the disease to a farm, if it is contaminated with the disease causing bacteria. Farm tools such as jembes or forks can transmit the disease when contaminated soil attaches itself to the tools. Soil pests such as nematodes and insects can also spread the disease from one area to another.


How to identify the disease

Diseased potato root and tuber


Any signs of drying or wilting of one or more potatoes in your shamba is an indication that your potato crop could be infected with bacterial wilt. All a farmer needs to do is to dig up potatoes from such plants. If the potato tuber has a black ring with white spots, then it is a clear sign that it is infected with bacterial wilt. Potato leaves that turn yellow may also be having the disease. Stunted potatoes or sections of a potato plant drying may also be a sign that bacterial wilt is present.


How to control bacterial wilt


Crop rotation: Bacterial wilt has no known cure, but farmers can control it by practising crop rotation. One of the biggest problems facing the control of many diseases including bacterial wilt is that farmers are unable to practice crop rotation mainly due to lack of knowledge on its benefits. Farmers in Kinangop region have successfully managed to control bacterial wilt through crop rotation especially with cabbages, recording increased potato yields.


Cabbages planted in rotation with potatoes eradicates bacterial wilt from the soil

Farmers should never rotate potatoes with any other plants in the potato family such as tomatoes, bananas, eggplants, capsicums, chillies or groundnuts.  Suitable crops that can be rotated with potatoes include cabbages, beans, peas, onions, carrots or grass. Crop rotation has other benefits such as pest control and even maintaining soil fertility.


Buy certified seed: Farmers should never buy potatoes meant for planting from their neighbours, if the potatoes are infected, the disease is transferred to your shamba. It is important to buy certified seed or from reputable potato growers who know more about bacterial wilt. New potato seeds should be planted in a field that has not been planted with potatoes the previous season.


Uproot diseased plants: All diseased plants should be uprooted together with the surrounding soil. The affected plants and tubers should be buried far away from the potato field or even burnt. Do not put diseased plants in a compost heap. Instead, you should burn them.


Select a good planting field: Potatoes should never be planted in low-lying or waterlogged areas. Upper sections of the farm where drainage is good are ideal for potato planting.


Remove volunteer potatoes: Potatoes that grow on their own after the previous crop are carriers of bacterial wilt and even pests. Such potatoes should be uprooted, burnt or buried far away from the shamba.


Proper weeding: Many weeds serve as hosts to bacterial wilt. Regular and proper weeding is important to prevent such weeds.


KARI now adopts sangi potato variety


Peter Gitau, a farmer from Karati area in Kinangop, introduced sangi potato variety into Kenya from Tanzania seven years ago. The government, however, classified it as a potato variety of “unkown”origin. The classification meant that research institutions including the Kenya Plant Health Inspection Service (KEPHIS), could not touch it.


Sangi has become the most popular potato variety with farmers due to its high yielding quality and resistance to some viral diseases, forcing the government to rethink its earlier view. But sangi cannot resist bacterial wilt. It is now the main carrier of the disease in the country because every farmer wants it.


The Kenya Agricultural Research Institute (KARI) is producing clean seed and selling it to farmers. However, the cleaning process for this variety is tedious and only a few bags have reached farmers this year.


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