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.
RWA
ENG