Cassava root is eaten as a vegetable and is considered to be toxic in raw form which is why it must be cooked before being consumed. The root has a variety of applications, some of which include the production of flour, starch, or ethanol. Cassava leaves can supply a good source of vitamins and protein which can also be consumed after cooking. Cassava hay is used as animal feed and it plays a role in the production of adhesives, textiles, and cosmetics.
Cassava, Manihot esculenta, is a perennial shrub in the family Euphorbiaceae grown primarily for its storage roots which are eaten as a vegetable. The cassava plant is a woody plant with erect stems and spirally arranged simple lobed leaves with petioles (leaf stems) up to 30 cm in length. The plant produces petal-less flowers on a raceme. The edible roots of the plant are usually cylindrical and tapered and are white, brown or reddish in color. Cassava plants can reach 4 m in height and is usually harvested 9-12 months after planting. Cassava may also be referred to as Brazilian arrowroot, manioc, yuca or tapioca and the origins of the plant are unknown. The plant is not known to occur wild but may have first been cultivated in Brazil. Cassava is the third-largest source of food carbohydrates in the tropics, after rice and maize. It is a major staple food in the developing world, providing a basic diet for over half a billion people. It is one of the most drought-tolerant crops, capable of growing on marginal soils.
Adekunle, A. A., Dixon, A., Ojurongbe, J, Ilona, P, Muthada, L & Adisa, S. Growing Cassava Commercially in Nigeria. Information and Communication Support for Agricultural Growth in Nigeria (ICS-Nigeria). Available at: http://www.cassavabiz.org/agroenterpr.... [Accessed 10 November 14]. Free to access.
CABI Crop Protection Compendium. (2008). Manihot esculenta datasheet. Available at: http://www.cabi.org/cpc/datasheet/17585. [Accessed 05 November 14]. Paid subscription required.
James, B., Yaninek, J, Tumanteh, A., Maroya, N., Dixon, A., Salawu, R. & Kwarteng, J. (2000). Starting a Cassava Farm. IPM Field Guide for Extension Agents. International Institute for Tropical Agriculture. Available at: http://www.infonet-biovision.org/res/.... [Accessed 10 November 14]. Free to access.
Circular or irregular brown spots with darker margin between leaf veins on older leaves; centers of lesions may drop out givinf leaves a shothole appearance; if infection is severe, leaves may turn yellow, dry out and drop from the plant
Disease emergence favored by high temperature and humidity
Remove leaves and crop debris from around plants to prevent disease spreading; remove weeds from around crop
- chlorotic or necrotic vein banding in mature leaves which may merge later to form large yellow patches
- Brown elongated necrotic lesions on young stems
- necrosis of tubers
- roots develop knots
- internal tissues of roots and tubers stained brown and may rot due to secondary fungus infection
1. yellowing along veins on lower/older leaves ~ 3 months after planting
2. dark brown spots on upper green portion of stem ~ 6 months after planting
3. Severe cases- leaf drying, shoot die-back
4. In Tuber - Brown and hard rot when you cut into it. Causes malformation and root
constriction ~ 10 months after planting
Histroy and origin: Disease is prevalent in East Africa (Tanzania, Uganda and Kenya). It was first reported in 1930's in Tanzania and become endemic in later years. It is currently travelling from East Africa westwards and has been reported in the DRC. There is considerable concern that it will appear in the major West African growing regions, notably Nigeria. The virus is transmitted through whiteflies and stem cuttings. The origin of CBSD is suspected to have arisen from the viruses that are already present on the indigenous African flora. Virus structure and properties: The microscopic studies revealed that the virus is 650 nm long and earlier it was believe to be carlavirus. But further studies associate the virus to Ipomovirus. Cassva Brown Streak Disease is caused by two distinct species of single-stranded RNA (ssRNA) viruses, Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), belonging to the genus Ipomovirus of the family Potyviridae. Economic loss: Cassava is an important stable crop in Africa and the continent produces an estimated 54% of the world's cassava production. As such the threat from CBSD seems inevitable due to its presence in many eastern African countries and its rate of transmission westwards to the major growing regions in Nigeria (which produced 30.8% of the world's supply). Though the economic loss from brown streak virus depends on region, cultivars and environment conditions, in general it is estimated up to 70% yield loss in susceptible variety is common with losses as high as 100% being observed in some regions. If the disease is unchecked it may cause 2 billion dollar in loss in Nigeria alone and lead to increase widespread poverty and malnutrition in West and Central Africa.
Disease diagnosis: The first and foremost important aspect is to identify the disease correctly. Cassava brown streak disease varies in symptoms which made it difficult to identify in the field. It makes further complicated if both cassava brown streak and cassava mosaic diseases occur together. There are few techniques like serological and molecular methods are used to identify the virus in laboratory but have their limitations. Planting materials: Use only healthy and disease free cuttings for planting. Resistant cultivars: Plant cassava varieties that are more tolerant of brown streak virus such as Garukunsubire and Seruruseke. Roguing and sanitation: Remove and destroy any plants which are symptomatic of the disease including alternative hosts. Early Harvesting of tubers: Harvest crop early to avoid severe losses due to necrosis of tubers. Follow proper plant quarantine practices to avoid spread of virus to new region. Control insect vector: Whiteflies can be controlled by encouraging beneficial insects in the field like spiders, ladybird beetles etc. Use yellow sticky traps to monitor infestation of whiteflies. Spraying insecticidal soaps under leaf surface to kill flies.
Discolored pale green, yellow or white mottled leaves which may be distorted with a reduced size; in highly susceptible cassava cultivars plant growth may be stunted, resulting in poor root yield and low quality stem cuttings. Note that infected plants can express a range of symptoms and the exact symptoms depend on the species of virus and the strain as well as the environmental conditions and and the sensitivity of the cassava host.
1. Patches of discolouration (chlorosis) in the leaves that vary from yellow to green.
2. The leaves display size variation and are often severely distorted.
3. Leaf blades sometimes fold depending on severity shrivel.
Disease is spread by infected cuttings and by whiteflies. The leaves are yellow, mottled and distorted. If leaves are yellow all over but are a normal size or there brown leaves that that does not indicate disease. Wild cassava (kisamvu cha mpira in Kiswahili) also hosts the disease. The disease was first observed in the late 19th Century in what is now Tanzania. It was not until work in 1938 that the disease transmission was confirmed to occur via grafting as well as vectored by the White fly.
Varieties of cassava resistant to the virus are available in many countries, most traditional varieties of cassava grown in Africa are susceptible to the virus, seek advice from an agricultural extension on suitable varieties for your region (see below). Do not plant cuttings from plants with symptoms of disease; inspect plants regularly for symptoms of disease and remove and destroy any showing symptoms. Infected plants should be uprooted ('rouged'). Replace with disease resistant varieties such as 'Rwizihiza', 'Ndamirabana', 'Cyizere', 'Seruruseke', 'Mavoka', 'Garukunsubire' and 'Mbakungahaze'. There is no agrochemical agent or organic treatment for this disease. There are both control strategies for the whitefly vector.
Small, angular, brown, water-soaked lesions between leaf veins on lower surfaces of leaves; leaf blades turning brown as lesion expands; lesions may have a yello halo; lesions coalesce to form large necrotic patches; defoliation occurs with leaf petioles remaining in horizontal position as leaves drop; dieback of shoots; brown gum may be present on stems, leaves and petioles
Most important bacterial disease of cassava; spread by water splash and infected tools; disease more severe in wet conditions; particularly destructive in South America and Africa; most important method of spread is probably through exchange of infected plant cuttings
Rotate cassava crop with non-host; plow crop debris into soil after harvest or remove and burn it; prune infected parts from plant; propagate cuttings only from healthy plants; intercrop cassava with corn (maize) and melon
Yellow stipping of leaves; chlorotic spots on leaves; chlorosis of entire leaves; if infestation is very high then leaves may be stunted and deformed; terminal leaves may die and drop from plant; pest responsible is a tiny green mite
1. Chlorosis (yellowing of leaves).
2. Leaves become shrivelled, mottled in serious cases
3. Check for the presence of mites on the underside of leaves
4. Yellow speckles evenly distributed on young leaves usually near the top ⅓ of the plant
Green spider mites are very common pests in most African growing regions and become problematic during the dry season; can cause significant tuber losses
Plant tolerant cassava varieties where possible; plant at the beginning of the rainy season to encourage vigorous growth which allows plant to tolerate attack; intercropping with crops such as cowpea may reduce damage; introductions of the predatory mite Typhlodromalus aripo have been very successful at controlling the green spider mite in many regions of Africa