Cowpeas grown for their dry seeds are also known as black-eyed peas and black-eyed beans.
They are most important in the semi-arid tropics where they are grown mainly for their mature seeds.
They withstand heat better than most other legumes and are very drought resistant.
Origin of Cowpea
Cowpea probably originated in central Africa. It spreads from there in remote times through Egypt or Arabia to Asia and the Mediterranean.
It was introduced by the Spaniards into the west indies in the 16th century and taken to the United States of America in about 1700.
The Ecology of the Plant
Cowpeas are widely distributed throughout the tropics and sub-tropics.
They can be grown under a wide range of conditions. They tolerate heat and relatively dry conditions.
It can be grown on very poor acid soils as a soil improver. It is photoperiod sensitive and is classified as a short-day plant.
Cowpea is an annual herbaceous legume. It has a short taproot with numerous spreading laterals which possess nodules.
The nodules are capable of fixing atmospheric nitrogen; up to 30-70 kg/ha per year.
The leaflets are relatively smooth and shiny.
The white or purple flowers are borne in pairs in short racemes.
The plants are largely self-pollinated but some cross-pollination occurs.
The growth habit of cowpea is indeterminate, the plant continues to blossom and produce pods over a long period until checked by adverse environmental conditions.
The pods are smooth and vary in length depending on the variety.
The seeds are variable in size, shape, and color; they may be globular to kidney-shaped and their color may be white, brown, red, black, or mottled.
Many varieties have been developed to suit the different ecological zones and consumer tastes.
Some of these are Vita 5 & IT84E-108 which are white; Ife brown, IT84E-124, and IT84S-2246-4 which are brown. The latter (IT84S-2246-4) is resistant to aphids, thrips, bruchids, e.t.c.
Cultural Practices of Cowpeas
In the forest zone, two crops can be grown. The first or early crop is down when the rains are available in April and the second or late crop is sown at the end of August.
Generally, the late crop is higher yielding and of better quality than the early crop because diseases and pests are fewer in the late season.
In the drier part where only one crop session is possible, planting is done in June or early July.
Weeds can be controlled manually at 3 and 7 weeks after planting.
Herbicides can also be used; e.g. gales at 2-3 kg a.I/ha, applied pre-emergence or early post-emergence within 14 days after planting.
The control of pests and diseases is a must for cowpeas.
The crop should be sprayed with nuvacron 60 at 30ml/9 liters of water weekly from the period of flowering.
Other insecticides that could be used include cymbush, decks, and karate. About 3-4 sprays should suffice.
Fertilizer application is not necessary especially if it is planted after a cereal crop that received fertilizers.
The plants are in any case able to fix atmospheric nitrogen. However, in every poor soil, a starter dose of 20kg/ha of N may be applied.
Cowpea responds to phosphorus and 20-40kg/ha P2O3 as single superphosphate could be applied just before planting by broadcasting and incorporating in the soil or at planting by side placement.
General fertilizer application may also be done with 200kg/ha of NPK 15.15.15 just before planting.
Cowpeas should be harvested when half to two-thirds of the pods have matured (when they turn brown).
The pods are handpicked and because the pods ripen unevenly, 4-5 pickings may be necessary.
After harvesting the pods, they should be further dried in the sun or mechanical driers.
This is particularly important if harvesting has been done in wet weather.
After the pods have dried, they are threshed. This is done by placing the pods in sacks, beating the sacks with sticks to split the pods, and then winnowing to separate the seeds from the chaff and other foreign matter.
Machines, which can shell Cowpea pods and clean the seeds are also available.
Under local conditions, cowpea yields vary widely between 250 and 1000kg/ha of dry grain.
With good management and adopting recommended practices, yields of 1,500-2,000kg/ha are possible.
The potential grain yield is estimated to be up to 3,500kg/ha.
Storage of Cowpea
The seeds can be stored in bags or sealed containers or polythene/plastic bags.
Storage is made easier if the seeds have been properly dried to a low moisture content of 10-12%.
Stores should be cleaned and fumigated. The equivalent of one tablet of phostoxin to 1000kg of grains will keep storage pests at bay.
The grains can be processed before storage by milling or grinding them into flour.
The flour is then packaged in transparent polythene sheets and can be preserved for longer periods in this form.
The dry pulse contains approximately
Uses of Cowpea
- Cowpea is used mainly for human consumption; it is boiled and eaten with vegetables.
Many African dishes can be made from cowpea flour, e.g. by frying the paste (‘Akara balls’) or boiling the paste that has been mixed with fish/eggs and oil (moin moin in Nigeria).
- It is used for forage, hay, and silage for livestock. As a silage crop, it is commonly grown mixed with sorghum.
- It is grown for soil improvement as green manure and as a good cover crop to restrict soil erosion.
Diseases that affect cowpea are the following but are not limited to these.
Wilt, caused by Fusarium oxysporum
Scab by Elsinore phaseoli
Stem Rot by Sclerotium rolfsii
Leaf spot by Cercospora canescens
Brown blotch by Colletotrichum app, etc.
Most of these can be controlled with fungicides like Dithane M-45 (mancozeb) and Benlate (benomyl) and the use of resistant varieties.
The pests of cowpea can be grouped into pre-flowering, post-flowering, and storage pests.
The Pre-flowering pests include leafhoppers (Empoasca spp.), cowpea aphid (Aphis craccivora), foliage beetle (Ootheca mutabilis), and striped foliage beetle (Medythia quaternary).
Spraying pre-flowering pests with insecticides is uneconomic.
Post-flowering pests include flower thrips (Megalurothrips sjostedti), legume pod borer (Maruca testulalis), seed moth (Cydia ptychora), blisters beetles (Mylabris spp.), pod sucking bug (Nezara viridula).
Post-flowering pests should be controlled with insecticides sprayed weekly.
The common storage pest is the cowpea weevil, Callosobruchus maculatus.
It is a pest of worldwide importance and severe infestations can lead to grain losses of up to 30% within six months of storage.
It is a field for storage pest. The characteristic holes made in the seeds by the pest make it easy to recognize infested seeds.
Phostoxin tablets, actellic, groundnut oil and neem seed oil applied to seeds can control storage pests.
Pest control in cowpea is best achieved through an integrated approach combining the use of insect-resistant cultivars and appropriate cultural practices with minimum insecticides application.
Nematodes affecting Cowpeas
Root-knot nematodes (Meloidogyne incognita, M. javanica, and M. Arenaria) are widespread throughout the tropics.
Nematodes cause extensive damage to cowpea root systems. Root-knot galls are easily distinguished from nodules containing Rhizobium, which are usually small spherical, and pink inside.
Nematocides can be used for control but these are uneconomic. Crop rotation may be effective in this regard.