Second only to maize, "Irish" potatoes play a very big role in the Kenya food security situation. Potatoes can be grown within a growing period of 3 months, produce good yields of highly nutritious food and be stored for some months under the right conditions.
However growing potatoes in mixed cropping systems as currently practised by many small scale farmers where volunteers from previous crops are not weeded out has by now managed to spread serious seed borne plant diseases to most potato growing areas. This has resulted in declining yields and again undermined the possibility of good food security in These areas.

In order to clean up the disease situation and to increase clean side production it is necessary to understand exactly what needs to be done (for more articles on clean seed potato production please also see TOF June 2010

Farmers can also grow their own seed and share with neighbours, if good field hygiene is observed as described in this article.

This involves maximising tuber production per unit area of limited, disease-free land through high-density planting in a seed plot and also separation of seed and ware (larger tubers meant for consumption) potato production. The system uses 50% less land than the ware production to meet on-farm seed tuber requirements

Clean seed tubers can be obtained from KARI centres at Tigoni, Embu, Kitale and Oljoro Orok, identified seed growers who work with Ministry of Agriculture, and from authorised farmers groups who produce quality seed with advisory inspection support from Kenya Plant Health Inspectorate Service (KEPHIS). However, commercial clean seed is expensive and mostly not available. Therefore, for most farmers, positive seed selection and seed plot system for seed production offer an immediate low-cost alternative, provided it is done correctly

This is a procedure where any diseased plant particularly infected with bacterial wilt or viruses is removed from the field immediately it is noticed and the remaining healthy-looking plants at flowering are marked with sticks or pegs. The marked or selected healthy-looking plants should be checked weekly and those which have developed disease symptoms should be unpegged and removed from the field. Pegged plants should not be near (at least 1 metre away) where diseased plants were removed.

A healthy plant is vigorous, has many stems, dark-green leaves and at harvest, has more seed-sized of 35-55 mm than smaller ones below 25 mm in diameter.

Sudden wilting of plants even when it is wet. Entire plants can wilt quickly without yellowing. There is a dark brown colour in the inner section of the stem. A white creamy liquid oozes out when the stem is cut near the base. Tubers are black or have black eye buds. Heavily infected tubers have soil stuck to the tuber eyes and on cutting of the tubers rotting from the vascular ring is observed

Plants are stunted (dwarfed). Leaves may have mosaic pattern (yellow and green). Leaf margins may be curled or rolled up and may be thick. In dry season, green aphids may be found on lower leaf surfaces. Tubers produced are small

Mark out beds of 2.0 m width and a sufficient length depending on your seed needs. Plant in furrows at a spacing of 30 x 30 cm at planting depth of 15 cm. Broadcast DAP fertiliser at the rate of 500 gm for every 10 m2. A 90 m2 seed plot (2 x 45 m) can provide enough material to plant 0.4 ha (1 acre) of ware potatoes (4000 m2). Hand weeding is recommended. Weeding should be done on appearance of weeds until there is sufficient potato growth to suppress weed growth.

Seed plot should be weekly inspected to monitor crop performance and particularly occurrence of pests (aphids, potato tuber moth) and diseases (bacterial wilt, viruses, early and late blight). Aphids can be easily controlled by spot insecticide application (consult area extension agricultural officers or the nearest KARI centre for advice). In case of potato tuber moth ridging is recommended. Any plant with bacterial wilt and/or virus infection should be uprooted and be destroyed and should not be used as animal feed as they may be brought back to the field in form of manure. Put 2 hands-full of ashes or 1 hand-full of lime in the hole after removing a wilted plant. Early and late blight can be effectively controlled by using appropriate fungicides immediately when noticed (consult area extension agricultural officers or the nearest KARI centre for advice)

On maturity, when leaves begin turning yellow, remove potato vines (haulms / stems) about 2 weeks before harvesting to harden tuber skin. Harvest when the soil is dry. Avoid injuring the tubers.

Tubers harvested from seed plots are divided into 2 lots: one lot is used to establish a new seed plot (for not more than 3 seasons) as described above and the other lot is used for production of ware potato in main fields.