Cowpeas

The land can be manually prepared using the conventional hand  tools (hoes or torias). In most settings where cowpea is grown on old plots, field preparations start immediately with cultivation/tilling of the land. However, production on virgin land should start with clearance of bushes using axes and machetes before proceeding to till the land.

Trees and shrubs in the site are cut down manually, or grasses slashed and fallen trees removed from the field. Ridging can be carried out after harrowing if ridge planting is required. At least five to seven days should be allowed between each operation to allow for decay of bushes/ grass and decomposition by micro-organisms, thus enhancing soil fertility for good seed germination and growth. It is important to choose soil from which high production of cowpea may be obtained. A farmer must therefore select a well-drained sandy-loam soil in areas of high rainfall.

Most cowpeas are intercropped  with other food crops such as sorghum, maize, millet and cassava. Pure stands are sometimes established near homesteads for their leaves to be eaten as vegetable.

Spacing in pure stands is very variable, very often 30 cm× 40 cm in off-season and 40 cm × 50 cm for early and erect varieties. A wider spacing of 50 cm × 75 cm for late or spreading varieties with 2 or 3 seeds per hill are commonly used. In some instances, spacing of 60 cm × 30 cm is also reasonable. Broadcasting is the more common method of sowing amongst rural farmers in Africa and South Sudan in particular where cowpea is sown with other food crops.The seeds are planted in 2 to 5 cm deep. However planting,  at 3 to 4 cm gives good germination hence plant stand.

(i) Fertilization

Cowpea grows well without fertilizer in fertile soils. In soils of low fertility, it responds to phosphorus and potash and often to some nitrogen. An amount of about 10 kg/ha of nitrogen applied at the time of sowing and 40 to 70 kg/ha of Potassium and Phosphorus fertiliser may be applied before planting.

(ii) Irrigation

Supplementary irrigation to cowpea field is important in areas where annual rainfall is less than 400 mm. During off-season, every other day irrigation schedule is necessary so that the plants can withstand the heat and water stress effect of the dry season high evapo-transpiration rate.

(iii)Weed Control

Weeds are serious problem in cowpea production. If not periodically removed they may act as hosts for pests. Thus, they will reduce both yield and quality of the grain. In addition, fodder yield may also be reduced since cowpea is not a strong competitor for resources particularly at the establishment stage. In other words, cowpea should be kept free of weeds after establishment. When left unweeded, cowpea can be completely smothered by weeds resulting in total yield loss. Weeds compete with crop, during growth, for light, water and nutrients. Weeds can cause greater yield reduction than arthropods, bacteria, viruses, fungi and diseases and may lower quality of the produce. Two weed control methods are commonly practiced in cowpea production:

(a) Manual weed control: this is the most common method used by farmers in rural South Sudan. The first weeding using hand hoes is carried out two weeks after planting followed by a second weeding in six weeks’ time. In high rainfall areas such as the Greenbelt, three weedings may be required.

(b) Chemical weed control: herbicide application is both safe and effective if a farmer can afford. However, its choice and time of application depends on the type of weed and availability of the herbicide to be applied

Pests

Insect pests are probably the most important factor limiting the yield of seed and quality of leaves used as vegetable.

The most important pests of cowpea include:

(a) Bean aphid (Aphis fabae): these aphids are black sucking insects, which cluster around growing points, stems, leaves and flowers. If in large numbers, they can prevent normal growth.

Yellowing and distortion of the leaves is common due to attack of these aphids. Spraying with malathion, menazon or endosulfan can control the spread of the insect pest in the cowpea field.

(c) Spotted cowpea pod borer (Maruca testulalis)

This is a pest of drier areas, which can cause damage to seed. The larvae are olive green with rows of dark spots and are hairy. They eat both the flowers and pods causing serious damage to the crop. If insecticides are to be applied to control pests, they must not be applied before the removal of leaves for vegetable.

(d) Bird damage

The mode of germination of cowpea is epigeal, that is, the cotyledons are carried above the ground. They assume photosynthetic function which supports growth, until the first true leaves are photo-synthetically competent. At this stage, birds especially doves, pigeons, guinea fowls and Double-supped Francolin Francolinus bicalcaratus ‘Kari’ (Moru) cut these cotyledons and eat them; thus destroying the germinated seedling at this early stage. Resowing of the destroyed seedlings can be done immediately. Guinea fowls can be a menace when seeds have been formed in the pods.

e) African Red Monkeys

Both the grey and brown African monkeys can eat the pods of the cowpea. They start eating the pods at the pod filling stage and if left unchecked, they can completely devour the crop with total yield loss. The only control is to keep watch over the crop from the  time pods are being formed until harvest.

f) Bruchids (Callosobruchus)

This is the main storage pest of cowpea. There are two major species: Callosobruchus masculatus and Callosobruchus chinensis. The adult beetles often lay their eggs in the field on the developing pods. The larvae bore through the pod walls and into the seeds. They are so small that their entry holes are almost invisible and as the seeds grow, the holes disappear. The larvae feed inside the seeds and each makes a tunnel almost to the surface. Only the seed coat is left intact, forming a window at the end of the tunnel. After pupation, the adult beetle emerges by pushing out the flap of seed coat, leaving a circular hole. Although some eggs are laid in the field, most are laid by adults emerging in the stores. They lay their eggs loosely amongst the seeds and can cause a rapid increase in the number of infected seeds. Farmers often mix cowpea seeds with ash; this is the mostly used control

Diseases

Diseases of cowpeas are more prevalent and serious in humid areas but they can also attack the plants in drier areas. The most common diseases that affect cowpea are:

(a) Zonate leaf spots

These are various spots on the leaves caused by Ascochyta phaseolorum and Dactuli phoratarii and pseudo rust (Synchytrium dolichi). Their control is mainly by growing  resistant varieties of cowpea to these fungal diseases. Septoria leaf spot, Cercospora leaf spot and brown blotch are some of the common cowpea leaf spots.

(b) Viral diseases

Cowpea is susceptible to more than 20 viral diseases, some of which include: cowpea aphid-borne mosaic, cowpea banding mosaic disease, cowpea chlorotic mottle virus, cowpea golden mottle virus, cowpea yellow mosaic and cowpea severe mosaic virus. Some are passed from one generation of plants to the next through the seed, and as a result, they can spread to other cowpea production areas through seed transfer. Seed borne diseases are spread within cowpea fields by insect pests such as aphids and beetles. Viral diseases are difficult to control using chemicals. The only possible control is the use of improved cowpea varieties with resistance to viral infection.

To make a good vegetable or spinach, the leaves of the cowpea plant must be young and tender; the best leaves are about the third and fourth from the apical end of the shoots. Removing all the tender leaves three times at weekly intervals, starting four or six weeks after sowing (planting)

have no adverse effect on grain yields although flowering may be delayed. In crops grown for the seed, 10–20 % of the  leaves are harvested before the start of flowering with little detrimental effect on the seed yield. Stronger defoliation (>40 %) increasingly reduces flowering, fruiting and seed yield.

Mature seeds are usually harvested by hand. Green pods are harvested when the seed is still immature, 12–15 days after flowering. Harvest of matured pods for dry seeds are usually done by removing matured pods individually as they ripen and are spread on the ground in the homestead to dry. In indeterminate maturing varieties, harvesting of matured pods is complicated by prolonged and uneven ripening; for some landraces harvesting may require up to seven rounds with three to four days intervals. The duration of the crop from sowing to harvesting depends largely on the growth habit, the rainfall and local husbandry practice but is seldom not more than five or six months.

The tender leaves are usually picked, crushed and fried and then boiled with meat or sesame or groundnut paste and eaten with ‘ugali/asida or kisra’. Sometimes the leaves are dried and ground into powder, which can be stored for later consumption in the dry season when fresh leaves are not available. Cooking before drying of cowpea leaves is a widespread method of preservation in many parts of Africa; boiled cowpea leaves are kneaded to a pulp and then squeezed into golf-ball size pallets that are dried and stored. The seeds may be boiled with maize or sorghum and eaten as “balila” or mixed with sesame or groundnut paste and eaten. In some communities, the boiled seeds mixed with sesame or groundnut paste is eaten with “ugali/asida”. The seed coat may be removed, after which they are boiled or fried and sesame or groundnut paste is added to make a sauce (pirinda), which can be eaten with “ugali/asida or kisra”.

Threshing

The pods of cowpea can be manually threshed by beating with a stick when harvested pods spread in the sun are well-dried. The seeds are breakable as such the threshing should be light,

just to break the pods. The pods can also be broken by fingers to remove the seeds, if the quantity is little.

Sorting

Seed quality is a determinant of good crop establishment, growth and development. Thus, care at all levels of operations; from harvesting, threshing and post-harvest handling to keep the seeds free of infection by pests and diseases is necessary. Sorting is crucial to remove defective and broken grains, stones, waste and infected seeds from healthy ones. It is in the interest of the seed dealers to get clean seed from seed farmers so that they get better pay.

Grading

The highly nutritious cowpea seed is grown for fresh, processed, and dried uses. Thus, healthy leaf and high quality seed is required for consumption and marketing. Grading can be done

by removing infested, diseased and broken seeds and leaves. Shriveled seeds are also eliminated.

Packaging

The seeds should be packaged in bags and placed into an electrical dryer or spread on a slab under the sun to ensure that the moisture content of the seed is reduced to the desired level of 12 % or less. Thus: cowpeas should be packed in suitable packages which must be clean, sound, and free from insect, fungal infestation and the packing material shall be of good grade and quality. Cowpeas can be packed in containers which will safeguard the hygienic, nutritional, technological and organoleptic qualities of the products. The containers, including packaging material, should be made of substances which are safe and suitable for their intended use. They shall not impart any toxic substance or undesirable odour or flavour to the product. Each package shall contain cowpeas of the same type and of the same grade designation. If cowpeas are presented in bags, the bags shall also be free of pests and contaminants. Each package shall be securely closed and sealed. For long period storage of cowpea, the Purdue Improved Crops Storage (PICS) bags should be introduced. The bag reduces loss of cowpea grain to insect infestation.

Storage

For seed, many farmers prefer storing the seed grain within the dry pod. The dried pods are tied in small bundles and hung over the cooking spot in the house/ kitchen so that whenever food is

being cooked the smoke from the fire would drive away invading insects. In some places, dried chillies are ground into powder

and sprinkled in a bag in which pods are kept. The hot chillies (piper nigrum) are reported by farmers to scare and repel away invading storage pests. Dried cowpea leaves as vegetable can also be stored in water proof containers to be eaten in the dry season when green vegetables are scarce.