GROWTH CONDITIONS
Growth period: 6–12 months for short-season sweet types and improved varieties.
Long-season types are often left in the ground for one or more years. Both types are
normally harvested as and when required for eating.
Temperature: the optimum is about 25–30°C. Intolerant of frost and cold weather.
Rainfall: 1000–2000 mm per year is optimum, but cassava can grow with 500 mm
or less. It can withstand long periods of drought, except at planting time.
Altitude: cassava is basically a lowland crop, though it is grown up to 1600 m near
the equator and up to 1000 m in the humid tropics.
Pests: not usually a big problem, but sometimes one of the following can cause
problems: Green Spider Mite and Mealy Bugs (spread from South America to Africa
in the 1970s), Stem Borers, Weevil Borers, Red Spiders and Scale Insects. Wild
game can also devastate sweet cassava crops.
Diseases: viruses are the most serious problem; two are described below:
- Mosaic Virus—young leaves become white or yellow (chlorotic) and are smaller
and distorted. Yields can be reduced by 95%. Transmitted by the Whitefly and by
planting infected cuttings. Control: use resistant varieties and clean stem cuttings for
planting, destroy infected plants. - Brown Streak Virus—mature leaves become chlorotic, but without distortion; the
stems have brown streaks, become shrunken and may die; roots become discoloured.
Transmitted in the same ways as Mosaic Virus. Common in the coastal regions of
East Africa, and mainly associated with low temperatures. Controlled with crop
rotation; some varieties have some resistance.
serious than Mosaic Virus in tropical Africa. Controlled with resistant varieties and
improved drainage.
YIELD
The tubers of cassava can rapidly rot or spoil when they are above ground, so they
are normally left in the field and only harvested when needed as food. However the
tubers can be stored for much longer periods if they are peeled, sliced and dried in
the sun.
Yields vary according to variety/growth period, soil type, cultivation method and
severity of disease attack, particularly by virus. It has been observed that varieties
with long thin leaf lobes often yield more than varieties with short wide leaf lobes.
In ideal conditions 80 MT/ha can be achieved, but the global average is closer to
10 MT/ha; the African average is about 8 MT/ha.
In 2004 FAO reported that the Cook Islands achieved the highest national average
yield, 25 MT/ha, and that Burkina Faso had the lowest, 2.0 MT/ha.
- Bacterial Blight (or Wilt) —caused by Xanthomonas manihotis, it is now more