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Cassava Mosaic Disease in Kenya
In Kenya cassava is grown in over 90,000 ha. with an annual production of about 540,000 tons. Cultivation is mainly in western Kenya comprising of Nyanza and Western provinces (60%), Eastern (10%) and Coast Provinces (30%). The crop is grown by small holder poor households for subsistence and it is an important food security crop. Major constrains of cassava production include pests and diseases, poor agronomic practices, low yielding varieties, high cyanide levels, lack of clean planting materials and long maturity periods.

Cassava mosaic disease (CMD) is the most important, as it results in highest yield losses. CMD was for over a century recognized on cassava, but was not considered a major problem. In the mid 1990s the situation changed dramatically when an unusually severe form of CMD caused yield losses of 80-100% on farmers’ fields. Between 1995-1998 annual yield losses of cassava was approximated at 150,000 metric tons valued at US$ 10 million. In Nyanza province alone, yields declined from 7-10 t/ha to less than 3 t/ha while the area under production has declined from 25,000 to 17,000 ha. The disease initially spread from Uganda to the neighboring Kenyan districts of Teso, and Busia, and has now spread to other districts in Western and Nyanza provinces forcing farmers to abandon cassava cultivation. All the local varieties have been devastated and affected farmers are experiencing acutely reduced incomes and general insecurity at the household level.

The International Institute of Tropical Agriculture (IITA) through the East African Root Crops Research Network (EARRNET) in collaboration with the Kenya Agricultural Research Institute (KARI) initiated a program in 1997 to mitigate the effects of CMD in western Kenya. Gatsby Charitable Foundation (UK), Office of Foreign Disaster Assistance (OFDA, USA) and Rockefeller Foundation pooled resources to restore cassava cultivation in the region. The main objective was to develop and distribute CMD resistant, high yielding varieties with good tuber qualities to farmers. This involved germplasm enhancement and exchange from Uganda. A total of 1404 clones have been introduced from Uganda to Kenya through Alupe Open Quarantine station for evaluations and 22 clones so far are under multiplication in 12 sites in Nyanza and western Provinces. The clones have been introduced and evaluated in KARI centers in preliminary yield trials, and advanced to on-farm trials through participatory evaluation in farmers’ fields.

To accelerate the multiplication and distribution of high yielding CMD resistant varieties, a three-tier (primary, secondary and tertiary) multiplication system was adopted to allow all classes of farmers’ access the clean planting materials. The selected clones are first bulked at primary sites which are usually government controlled sites (Farmer Training Centers, Government Prison Farms, Research Institute farms), then moved to secondary sites at district levels which are managed by the district steering committees especially lead by the Ministry of Agriculture Extension Staff. The materials then trickle to tertiary multiplication sites managed by individual farmers, farmer groups and other partners (NGOs, CBOs etc).

Although large quantities of planting materials have been produced at primary level, this has not translated to farmers planting large areas, which indicates losses of planting materials as they move from primary, secondary, and finally to tertiary sites and the farmers. Although most primary bulking sites have irrigation facilities secondary and tertiary bulking sites rely on rainfall. Low and poorly distributed rainfall leads to poor sprouting and growth of the cassava cuttings, reducing the number of cuttings available for the next stage. In some of the secondary and tertiary bulking sites the establishment has been less than 60%.

At the tertiary sites , farmers do not usually conserve cassava planting materials after harvesting the roots during the dry spell. In some cases livestock are allowed to graze in the cassava fields. This results in the cassava planting materials drying and being used as fire wood or destroyed by grazing livestock. The multiplication of CMD free planting materials requires phytosanitary measures such as roging or uprooting of diseased plants. Poor food insecure households involved in bulking at tertiary levels are sometimes reluctant to rogue the diseased plants resulting in the spread the disease, reducing the amount of planting materials.

In Kenya, there have been two important trends concerning the status of CMD. Since the onset, promotion of CMD free planting material has been concentrated mainly in western Kenya districts of Busia, Teso and Siaya where symptoms were noted first in Kenya. 

  • Data from areas of Western Kenya towards the border with Uganda showed reduction in both incidence and severity of CMD in comparison with the previous years1 (Legg 2003). 
  •  There is evidence for continued movement of the severe CMD infection into southern Nyanza (Homabay , Kuria, Migori, Rachuonyo, Suba and Gucha districts)
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