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Cassava brown streak virus and Ugandan cassava brown streak virus Two virus species of the genus Ipomovirus (family Potyviridae) · formerly or also: CBSV, UCBSV
Cassava brown streak disease rots the storage roots of cassava from the inside: roots that look normal at harvest show dry, brown, corky patches when cut and are unfit to eat or sell. Leaves of infected plants may show only faint yellow patches along the veins, so farmers often spread the disease unknowingly in planting cuttings. It has spread from the East African coast across the Great Lakes region since the early 2000s and threatens cassava, the staple of hundreds of millions of people.
Cassava brown streak disease is caused by Cassava brown streak virus and Ugandan cassava brown streak virus Two virus species of the genus Ipomovirus (family Potyviridae), a virus (ipomoviruses with RNA genomes), spread mainly by infected cuttings and by whiteflies (order Patatavirales, family Potyviridae).
Older or alternative scientific names: CBSV, UCBSV.
Long known in the coastal lowlands of East Africa (Tanzania, Kenya, Mozambique, Malawi). A new epidemic emerged in Uganda in the mid-2000s and spread through the Great Lakes region into Rwanda, Burundi, the Democratic Republic of Congo, Zambia and beyond. It has not been reported from West Africa, Asia or the Americas, where it is a major quarantine concern.
| Region | Status |
|---|---|
| East African coast | Endemic since at least the 1930s |
| Great Lakes and Central Africa | Epidemic spread since the 2000s |
| Southern Africa | Present in Mozambique, Malawi and Zambia |
| West Africa, Asia and the Americas | Not reported; quarantine concern |
Two ipomoviruses, detected by laboratory tests (RT-PCR). They are spread mainly through infected stem cuttings used for planting, and over short distances by the whitefly Bemisia tabaci in a semi-persistent way (the whitefly retains the virus only for hours).
| Crop stage | What you see |
|---|---|
| Leaves (mature leaves of established plants) | Yellow, feathery chlorosis along secondary veins or blotchy yellow patches on older leaves; symptoms vary with variety and season and can be absent. |
| Stems | Brown, elongated streaks or lesions on green stems; dieback of shoot tips in susceptible varieties. |
| Storage roots | Dry, brown to yellow, hard corky necrosis inside the roots, sometimes with constrictions on the surface; damage increases the longer roots stay in the ground. |
Most new infections come from planting cuttings taken from infected plants, many of which look healthy. Whiteflies spread the viruses between nearby plants, mostly in the first months after planting. Root necrosis develops progressively as the crop matures.
| Stage | Duration | Notes |
|---|---|---|
| Infected cutting planted | At planting | Main route of spread over distance. |
| Whitefly transmission | Minutes of feeding; whitefly infective for a few hours | Semi-persistent; local spread. |
| Leaf and stem symptoms | Weeks to months | Often mild or absent. |
| Root necrosis | Develops from about 6 months after planting | Increases with crop age. |
Spread is linked to whitefly abundance, which is greatest in warm conditions; symptom expression varies with temperature and season.
Continuous where cassava is grown and replanted from cuttings.
Using cuttings from unchecked or infected fields, exchanging planting material across regions, high whitefly numbers, susceptible varieties, and leaving roots in the ground long after maturity.
There is no economic threshold; management is preventive through clean planting material and tolerant varieties. In areas where the disease is absent, any detection is reported to the national plant-protection service.
Root necrosis makes much of the harvest unusable; losses of up to 70% or more of root yield are reported in susceptible varieties, and the disease costs East and Central African farmers heavily each year.
Control works best as a sequence: prevent, monitor, then act only when a threshold or a risk forecast says so, using the least disruptive option that works.
No chemical controls the viruses, and insecticides against whiteflies are not economic in most cassava systems. What is registered differs by country and changes over time; follow the label and your local plant-protection authority.
Cassava and some wild Manihot species; a few other plants have been infected experimentally.
How to grow the crop well is the first line of defence. Laisha's free grow guides cover each crop from sowing to harvest:
Written by Laisha from the sources above, in its own words. This page is general reference, not a prescription: confirm identification locally and follow the label and your plant-protection authority.