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April 06, 2008

Disease affects rice crop in Kenya

Rice farmers in Kenya's Kirinyaga District are counting their losses after their crop was attacked by the Rice Blast disease.

The farmers have been complaining about the disease, which has wiped out almost half of their crop. “It started last year and since then it has been spreading very fast,” said Mr Francis Gichovi, a rice farmer in Mwea.

The disease is now threatening to drastically reduce harvests this season. An acre of land under rice usually produces on average 25 bags of rice, but this may reduce to 10 bags, Mr Gichovi said.

Many rice scientists consider it to be the most devastating rice disease worldwide. It has been detected in 85 countries.It is caused by the fungus magnaporthe grisea and is characterized by the appearance of lesions on the leaves, nodes, and panicles.

Besides attacking the leaves, the fungus may also attack the stem at the nodes, causing the neck to rot, or at the panicle, causing panicle blast. When this occurs, yield losses may be large because few seeds in the panicle develop. “The rice plants have turned white and there is no seed in them,” explains Gichovi.

According to the district agricultural office in Mwea, the disease has been spurred by the rains, which have been unusually high this season.

The disease thrives in long periods of moisture, high humidity, little or no night wind and night temperatures of around 20°C. Poor crop rotation practices have also allowed the disease to spread.

According to experts, successful control of the disease usually requires an integrated management programme, including the use of resistant varieties, cultural practices and chemical control.

Farmers have been advised to burn diseased rice straw and stubble. This is an important control measure that reduces the disease prevalence, but will not provide complete control by itself. Use of clean seeds whenever possible is also being encouraged to help control the disease, seed treatment to eliminate blast is under study.

Continuous flooding is also recommended to limit its development. Fungicides used in the past have not been effective in tackling the disease.

Plans to screen and breed resistant varieties are in progress. Varietal resistance is the most economical way to control the disease.

Resistance to the disease in the plant is effective against attack at all stages of growth. However, the fungus is highly variable--new forms can appear which attack resistant varieties.

Some fungicides control neck rot or panicle blast. Even though they are expensive, they may be economical to use at this stage.

Business Daily Africa

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