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.
Harvested cassava roots
Researcher working in cassava field
Cassava thrives in tropical and subtropical regions of the world as it requires warm temperatures for optimal growth. The plants require at least 8 months of warm weather, thriving in regions with warm, moist climates with regular rainfall. Cassava can be grown in many types of soil, producing even in poor soil but but will be optimally productive in well-draining, sandy clay loam with a pH between 5.5 and 6.5. Cassava is drought resistant but will not tolerate water-logging. Root production is maximized when temperatures are between 25 and 32°C (77–90°F). Cassava should be planted in full sun and is very sensitive to shading, which leads to low yields.
Cassava is propagated from stem cuttings as the tubers do not produce buds. Stem cuttings should only be taken from plants which are free from disease, are at least 10 months old and havee borne tubers. The cuttings should be taken from hardened stems leaving at least 30 cm (11.8 in) of stem intact in the ground. The stem can be severed using a sharp knife, secateurs or saw and each cutting should have 1-2 nodes and be approximately 20 cm (7.9 in) long.
It is a good idea to dip the stem cuttings in an appropriate fungicide prior to planting to help prevent the development of diseases. The cuttings can then either be planted directly into a nursery bed or presprouted in trays or polyethylene bags. To presprout the stems, plant in a cell tray or bag which is filled with good quality soil. Plant one stem in each cell or bag by pushing it into the soil in the direction in which it was growing on the mother plant (oldest part of stem first). The trays should be kept in partial shade until the stems begin to sprout. If planting stem cuttings in a nursery bed (best for cuttings taken from higher up the stems where the wood is not mature), select a site with good quality soil in partial shade and prepare a bed at least 1 m (3.3 ft) wide. The stems can be planted horizontally in a nursery bed and this encourages the growth of multiple stems. Space the cuttings 10 x 10 cm (4 x 4 in) grid. Stem cutting should be watered immediately after planting and on a regular basis thereafter. Aim to keep the soil moist but not wet. Stems should begin to sprout 7-10 days after planting.
Plants propagated from stem cuttings are ready to be transplanted after approximately 4-6 weeks. Prepare the field for planting by cultivating the soil and removing weeds. Space transplants 75–100 cm (2.5–3.2 ft) apart in rows spaced 1–-5 m (3.2–16.4 ft) apart. Fertilize the plants as appropriate. Manure or poultry droppings can be used. Cultivate the soil to remove weeds and break up the soil around the plants.
Cassava is ready to harvest about a year after planting depending on the variety being grown. Some early maturing varieties may be ready to harvest in around nine months. In colder regions, cassava tubers can remain in the ground for up to 2 years before harvesting but can become fibrous so this is not recommended where cassava is being grown for consumption. Cassava tubers are harvested by digging. The roots should be dug up carefully to prevent damage.
Cutting cassava stems
Planting cassava stem cuttings
Cassava plantation in the Democratic Republic of Congo
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.
Common Pests and Diseases
Category : Fungal
Symptoms of a severe anthracnose infection on cassava stem
Anthracnose canker on cassava stem
Cankers on stems and leaf petioles; leaves drooping downwards; wilting leaves which die and fall from plant leading to plant defoliation; death of shoots; soft parts of plant become twisted and distorted
Anthracnose usually does not cause large-scale economic damage to cassava and control is usually not necessary; avoid planting cuttings with cankers; if disease does occur crop debris should be removed and destroyed after harvest
Cassava Brown Leaf Spot
Brown Leaf Spot on cassava leaf in Chambezi, Tanzania
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
Remove leaves and crop debris from around plants to prevent disease spreading; remove weeds from around crop
White leaf spot
Large, diffuse white spots on upper surface of leaves; spots with grey center on underside of leaves in humid weather
Remove leaves and crop debris from around plants to prevent disease spreading; remove weeds from around crop
Cassava witches'-broom phytoplasma
Symptoms of the disease include change in color of the stem and oozing from the stem
Cassava cuttings infected with witches broom disease
Witches' broom symptom
Plants are stunted with an excessive proliferation of branches; shoots have small leaves and shortened internodes; no chlorosis is present; cuttings from the shoots are weak but show no visible symptoms; few shoots successfully grow from cuttings.
Remove and destroy and plants suspected of being infected; remove all cassava debris from field after harvest; disinfect all tools and equipment between cuttings.
Category : Viral
Patches of dark brown or gray fungal growth on stems; necrotic areas covering buds on the stem
Only plant cassava cuttings taken from healthy plants which are free from necrotic lesions; space plants widely to allow good air circulation around plants and reduce disease incidence; remove weeds around plants; id disease is present, burn all necrotic stems and crop debris immediately after harvest to prevent spread
Cassava Brown Streak Disease
Cassava brown streak virus (CBSV)
B. tabaci feeding on the underside of cassava leaf
Tuber necrosis caused by Cassava brown streak
Root symptoms of CBSD
Root symptoms of CBSD
Mottled leaves infected with Cassava brown streak
Rotting tuber caused by Casava brown streak
CBSD symptoms on the lower leaves of a
cassava plant, Kenya
CBSD on lower leaf of cassava plant in Chambezi, Tanzania
- 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
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.
Cassava Mosaic Disease
African cassava mosaic virus (ACMV)
ACMV-infected cassava plant
Severe CMD symptoms on cassava leaf in Namulonge, southern Uganda
Cassava farmer showing severe damage to cassava roots infected with CMD
Resistant cassava variety beside a traditional susceptible variety with symptoms of ACMV
Whiteflies on cassava leaf
Field in Kwimba, Mwanza Region, Tanzania devastated by CMD in the space of one season
Cassava leaves showing typical mottling caused by ACMV
Whitefly nymphs on cassava leaf
Severe CMD symptoms on leaf in Chambezi, Tanzania
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.
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.
Category : Bacterial
Cassava Bacterial Blight
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
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
Category : Other
Cassava Nutritional Deficiency
Category : Bacterial, Fungal
Cassava root rot disease
White fungal structures visible on stem
Rotting tubers cut open to reveal discoloration
Fusarium rot-infected cassava roots
Discoloration on tuber surface caused by root rot
Fusarium-infected cassava stems
Dark tuber discoloration caused by Botryodiplodia
Cassava roots infected with botryodiplodia root rot disease
Leaves on affected plants turning brown and wilting and plant has a scorched appearance; leaves may remain attached to the plant or drop to the ground; plant death will occur; examination of roots reveals root dieback and swelling of tubers; tubers may have light brown, dark gray, blue or pink discoloration; rotting roots may be soft and produce a foul odor; infection by Botryodiplodia fungi may cause the appearance of white fungal structures at the base of the stem, particularly during the wet season
Plant cassava in well-draining soils; remove and destroy all crop debris by burning; sanitize all tools after use
Category : Insects
African root and tuber scale
Scales on cassava tubers
Scales on cassava stem
Oval shaped scales on stems, roots and/or tubers; infections which occur at an early age kill plants and prevent the production of tubers; plant becomes shriveled and discolored at feeding sites
Improve soil by adding organic matter to make soil more fertile; remove and destroy infested stems; do not plant cuttings with scale
Stem surfaces covered with white waxy substance; leaves wilting and dropping from plant; severe infestations may result in stunted plants and poor tuber yields; cutting from infected plants do not sprout; insect is a flattened oval scale with an elongated white cover
Plant material that is completely free of scale insects; remove and destroy infested stems from existing plantations; apply organic matter to soil to improve fertility
Grasshoppers (Variegated grasshopper, Elegant grasshopper)
Grasshoppers feeding on cassava leaves
Defoliated plants; bark removed from stems; insects are large brightly colored grasshoppers
Hand pick any grasshoppers found on plants; locate any egg pods around cassava field and destroy to reduce grasshopper populations; biopesticides such as "Green Muscle" are available in South and West Africa which are very effective at reducing the grasshopper population; products containing neem have also given good control of variegated grasshoppers
Category : Mites
Cassava Green Mite
Predatory mites feeding on the eggs of cassava green spider mite on the under surface of cassava leaf.
Cassava green mite infestation
Cassava green mite infested cassava leaves
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
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
Cassava Red Mite Damage
Two-spotted spider mite
Male of the green form of the spider mite Tetranychus urticae
Two females with an egg of the green form of the spider mite Tetranychus urticae.
Leaves stippled with yellow; leaves may appear bronzed; webbing covering leaves; mites may be visible as tiny moving dots on the webs or underside of leaves, best viewed using a hand lens; usually not spotted until there are visible symptoms on the plant; leaves turn yellow and may drop from plant
Spraying plants with a strong jet of water can help reduce buildup of spider mite populations; if mites become problematic apply insecticidal soap to plants; certain chemical insecticides may actually increase mite populations by killing off natural enemies and promoting mite reproduction
Category : Nematodes
Root knot nematode
Galls on roots which can be up to 3.3 cm (1 in) in diameter but are usually smaller; reduction in plant vigor; yellowing plants which wilt in hot weather
Plant resistant varieties if nematodes are known to be present in the soil ;check roots of plants mid-season or sooner if symptoms indicate nematodes; solarizing soil can reduce nematode populations in the soil and levels of inoculum of many other pathogens