Cowpea, popularly referred to as beans, is the most economically important indigenous African legume and most versatile African crop which feeds people, their livestock, the soil and other crops. In Nigeria it is simply known as ‘beans’. If you ask a layman in Nigeria what cowpea is, you would have a hard time finding the right answer but once you say Beans, they know exactly what you mean. There are two major varieties that are popularly known to people in southwest Nigeria; sweet beans or honey beans (ewa oloyin) and Nigerian brown beans (ewa drum).
There are a lot of great reasons why one should cultivate this crop; it can tolerate low rainfall and shortage of water, performs well in a wide variety of soils, and being a legume, it replenishes low fertility soils when the roots are left to decay, which makes it an ideal crop for crop rotation.
Cowpea is an annual herb which has a growth form that varies; it can be bushy, trailing, erect or climbing. Its root is a taproot which is quite strong and with many spreading lateral roots in surface soil. The stems of cowpea are striate, smooth or slightly hairy. Its leaves are in alternate pattern and are trifoliate, the colour of the leaves is dark green and shape varies from linear-lanceolate to ovate. Cowpea seeds also vary in size, shape and colour and the number of seeds per pod also varies.
Cowpea is an important economic crop, because of its various attributes such as: ability to adapt to different type of soils and suitability for intercropping, it grows and covers the topmost soil which in turn prevents erosion, all parts of Cowpea are useful even the leaves which can produce 9 times the calories, 15 times the protein, 90 times the calcium and thousands of times more vitamin C and beta-carotene of cowpea seed. Cowpea also complements a lot of cereal crops.
The inter-row and intra-row spacing depends on the type of variety of cowpea grown and the growing pattern, but generally for grain production, a plant population of 200,000 to 300,000/ha at 30 to 50cm inter-row spacing is preferred. The seed should be planted at 3cm to 4cm deep. Planting should be timed in relation to the maturity period, such that the crop is harvested in bright dry weather. It’s best to sow when the soil is moist or wet, i.e. when the rainfall is reduced. The date of planting should be timed in such a way that will allow the crop to escape from periods of high pest, and harvesting to coincide with the period of dry weather because harvesting under humid cloudy weather favours pod rot.
If the farmer is to plant cowpea twice in a year it is advised for the first crop be planted in April and the second in late July to mid-August, if planting the same variety the older seeds should be planted not the recently harvested seeds, because seeds that are not properly dried fail to germinate well and plant stands are reduced. Also, seeds that will be planted must be sorted to make sure that they are free from insect damage that is it has no holes or wrinkles and are disease free.
PEST & DISEASES
Cowpea is affected by a variety of diseases - fungal, bacterial and viral disease and these affects cowpea in different ways at different stages of growth.
Root Rot is caused by fungi, due to either damp weather or too much of moisture in the soil.
Stem Rot is caused by Phytophthora vignae, it occurs mainly in wetter coastal and sub-coastal areas, also occurs on waterlogged soils.
Mosaic virus affects leaves, the infected leaves are smaller than the healthy ones, and edges of the leaf are curly, generally the infected plants are more dwarfed and bushy, than non-infected plants. The disease also affects the formation of the pod.
Fusarium Wilt affects the leaves, it causes the lower leaves on one side of the plant to turn yellow, and plants infected are usually stunted and wilted. In order to control Mosaic virus and Fusarium Wilt it is s best to plant tolerant or resistant varieties. Although in the case of Fusarium Wilt root-knot nematode control practices should be followed since nematodes increase plant susceptibility to Fusarium wilt, and Cowpea is susceptible to nematodes, so it should not be planted consecutively on the same land. Other major and common diseases of cowpea are Anthracnose, Sclerotium stem, Damping off, Cercosporaleaf spot, Septoria leaf spot, Scab, Bacteria blight (Xanthomonas vignicola) etc.
Some general control measures include:
Plant only unaffected seeds
Use a resistant variety
Remove and bury infected plants
Make use of Crop rotation
Apply chemicals (fungicide and herbicide)
Topsoil that have been contaminated should be ploughed to reduce the incidence of pathogens
Treatment of seeds
Pest control: Cowpea is attacked by various Insect pests, during different phases of its lifecycle even down to storage. This is a major constraint to Cowpea production especially in West Africa, because their damage can be as high as 80-100% if not well managed.
Cowpea should be intercropped or mixed cropped and also grown as a cover crop for average yields to be attained. Cowpea should be harvested when the pods are fully mature and dry, but these pods do not mature at the same time because of its staggered flowering period. Cowpea varies in its growth habit from erect to semi erect types. Cowpea that is grown for vegetable purposes are picked 4 weeks after planting. One can either use hand or combine harvester to harvest the crop. More than 11 million hectares are harvested annually worldwide, 97% is from Africa and Nigeria harvests 4.5 million hectares annually. After harvesting, it is best to sun dry the pods and then thresh them immediately. This is important because drying reduces the moisture content of the grains, before storage in order to avoid the seed getting mouldy.
IITA (2009) noted that there is a big market for the sale of Cowpea grains and fodders in West Africa and in Nigeria farmers who store Cowpea fodder for sale at the peak of the dry season have been found to increase their annual income by 25%. It also serves as income generating avenues for other value chain actors within the cowpea chain. Cowpea ensures returns for both the marketers and producers which in turn aids sustainability of the system.
About 5.4 million of tons of dried cowpeas are produced worldwide from 11 million hectares, Africa produces nearly 5.2 million and Nigeria harvests 4.5 million hectares annually. In most parts of Nigeria Cowpea is been processed into other by products such as moin-moin, bean cake, bean soup etc. It contains 20%-25% of protein and 64% carbohydrate and has potential for poverty alleviation and malnutrition amongst the poor; also all parts of cowpea are useful, its vegetative part is good feed for cattle. This shows that all over Nigeria Cowpea is consumed in so many forms, thereby increasing the demand for cowpea.