Farmers in the southern districts of Kamonyi and Ruhango have expressed concerns following an infestation of their cassava plantation by cassava brown streak disease (CBSD), which has decimated dozens of hectares of their plantations.

So far, Rab estimates the damaged cassava plantations to be hundreds of hectares.

CBSD, locally known as Kabore, is a devastating disease that causes loss of cassava root (tuber) production and quality. The root rot resulting from the viral disease renders the cassava tuber inedible.

Gervais Gashaka, the head of research on cassava at Rab, said: "I cannot establish the actual damage since we are still surveying all the cassava fields but out of about 160 hactares of plantation surveyed, about 100 hactares were affected,” he said.

Gashaka said the extent of damage varies from one plantation to another, adding that this will probably affect the production of the Ruhango-based Kinazi cassava processing plant which highly relies on cassava harvest from Ruhango and other districts in the Southern Province.

He said it was the first time the viral disease was attacking the province.

"The first symptoms of the disease appeared in 2009,” he said, adding that the disease had for long ravaged cassava plantations in neighbours Tanzania, Kenya and Uganda.

"The disease was noticed after Rab distributed improved varieties to farmers in the province,” Gashaka said.

"But this year has seen the disease spread. Before, people were growing cassava and got good yields. The disease was latent then,” he added.

Before CBSD disease, cassava crops were prone to Cassava Mosaic virus Disease (CMD), locally known as Kubemba, a disease that makes cassava plants produce few or no tubers depending on the severity of the attack and the age of the plant at the time of infection.

Rab says the improved cassava cuttings that it has been producing are immune to CDM, but prone to CBSD. The cassava variety which is most popular to farmers in the Southern Province is I92/0057, locally known as Cyizere.

Looking for remedies

The Minister for Agriculture Dr Geraldine Mukeshimana, said a lot is being done to help farmers whose plantations were devastated by the disease. However, she said some interventions may not be immediate.

"Various interventions are being made, including helping farmers get cassava cuttings that are free from the viral disease, to plant. There are other cassava varieties that are being tested in the seeds development and multiplication centres to see which varieties are resistant to and free of CBSD though this cannot offer an immediate solution to farmers,” she said.

Gashaka said Rab is working hard in all its research stations, including Rubona, Karama and Nyagatare to get cassava cuttings to give to farmers. But this, he says, will take some time because for the cuttings to be mature for planting, there is a need to test their produce and resistance level, which necessitates about 24 months. However, he said they are looking for areas where they can get safe cassava cuttings for immediate help.

Gashaka also said there is need to carry out awareness campaigns aimed at informing farmers about CBSD so that they can help check its further spread.

"Farmers are not aware of the disease, so we will equip them with relevant information about the cause and remedy so that they can prevent it,” Gashaka said.

He added that Rab research department will work with crop research experts from the region to harmonise research activities and build synergy in finding tolerant or resistant cassava varieties to CBSD or how to effectively control the disease.

Research by Natural Resources Institute, University of Greenwich Chantam Martime, UK shows that DBSD was first identified in 1930s in Tanzania and its most likely vector is a whitefly.

The symptoms of CBSD cannot be recognised easily by untrained or inexperienced people, and may not appear until the cassava plant has stayed longer than nine months.

To manage the disease, it is recommended that all infected cassava plants be uprooted and destroyed to avoid disease build up and spread.

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