Cowpea production
Land Preparation
Cowpea requires a good, well-drained soil. In the forest zone, cowpea may not be grown as the first crop on lands that have been in fallow for more than 10 years. Cowpea should be rotated with other crops, e.g., maize, after one or two successive cropping. http://www.cassavabiz.org/agroenterprise/ent%20images/cowpea_02.pdf
For soils with poor structure, high run-off and low water infiltration, the physical properties can be improved markedly and cowpea yields increased if farmers hoe the land or the land is ploughed. Zero tillage (for example using Roundup spray prior to planting) may be used only where drainage is good. https://csirsavannah.wordpress.com/2012/12/04/production-guide-on-cowpea-vigna-unguiculata-l-walp/
Site must be stumped, ploughed, and harrowed into a clean seed bed. In sole cropping, it is not necessary to make ridges or heaps, but in mixed cropping, cowpea may be planted on ridges or heaps. Contour bunds are advised on sloping sites to check erosion. Also, if the land had been previously cropped, these land preparation requirements may not be necessary. ‘minimum tillage’ practice can be adopted.
When minimum tillage is practiced, spray Paraquat (Gramoxone) at 240 ml–320 ml/20 litres of water (3–4 litres/ha), depending on weed situation, to clear the vegetation. When there are stubborn weeds e.g. Imperata cylindrica (speargrass) and sedges, use Glyphosate (Round-up) at 5–6 litres/ha. If Round-up is used, the farmer is advised to wait for about 3 weeks before planting cowpea. http://www.cassavabiz.org/agroenterprise/ent%20images/cowpea_02.pdf
Variety
Recommended varieties
- Ife Brown (IRAWO), brown seeded, (75 days maturity).
- Ife Bimpe, Brown seeded, (85 days maturity).
- IT 84E–124, Brown seeded, (60 days maturity). (iv) K-28, Brown seeded, (about 75 days maturity). (v) IT 84E–2246-4, Brown seeded. Certified seeds are available from state Ministries of Agriculture and Natural Resources, the National Seed Service, and registered private seed companies. http://www.cassavabiz.org/agroenterprise/ent%20images/cowpea_02.pdf
Climatic and soil requirements
Cowpeas grow best during summer. The base temperature for germination is 8,5 °C and for leaf growth 20 °C. Cowpea is a heat-loving and drought-tolerant crop. The optimum temperature for growth and development is around 30 °C. Varieties differ in their response to day length, some being insensitive and flowering within 30 days after sowing when grown at a temperature around 30 °C. The time of flowering of photosensitive varieties is dependent on time and location of sowing and may be more than 100 days. Even in early flowering varieties, the flowering period can be extended by warm and moist conditions, leading to asynchronous maturity. The optimum sowing times are December to January. Early-sown crops tend to have elongated internodes, are less erect, more vegetative and have a lower yield than those sown at the optimum time. The presence of nodular bacteria specific to cowpea (Bradyrhizobium spp.), make it suitable for cultivation in the hot, marginal cropping areas of Southern Africa, as well as in the cooler, higher rainfall areas. However, cowpeas are much less tolerant to cold soils. Cowpeas grow best during summer. Water Cowpea is a higher drought-tolerant crop than many other crops. It can grow under rainfall ranging from 400 to 700 mm per annum. Cowpeas are also having a great tolerance to waterlogging. Well-distributed rainfall is important for normal growth and development of cowpeas. The frequency and unreliability of rainfall pose problems to cowpea growth in South Africa. In some areas, the frequency of rain is too high, resulting in flooding, while in some other areas it is so unreliable that moisture conservation remains vitally important for crop production. Cowpeas utilise soil moisture efficiently and are more drought-tolerant than groundnuts, soya-beans and sunflowers. Cowpeas can be produced satisfactorily with an annual rainfall between 400 and 750 mm. In some areas of Mpumalanga, where annual rainfall is high, cowpeas could be planted ata time to coincide with the peak period of rainfall during the vegetative phase or flowering stage so that pod-drying could take place during dry weather. Adequate rainfall is important during the flowering/pudding stage. Cowpeas react to serious moisture stress by limiting growth (especially leaf growth) and reducing leaf area by changing leaf orientation and closing the stomata. Flower and pod abscission during severe moisture stress also serves as a growth-restricting mechanism. Cowpeas are grown on a wide range of soils but the crop shows a preference for sandy soils, which tend to be less restrictive on root growth. It is more tolerant to infertile and acid soils than many other crops. Cowpeas are grown on a wide range of soils but prefer sandy soils which are less restrictive to root growth. This adaptation to lighter soils is coupled with drought tolerance through reduced leaf growth, less water loss through stomata, and leaf movement to reduce light and heat load under stress. Cowpeas are much less tolerant to cold soils than common beans and show a poor tolerance to waterlogging. Cowpeas thrive in well-drained soil and less on heavy soils. It requires a soil pH of between 5,6 and 6,0. http://www.arc.agric.za/arcgci/Fact%20Sheets%20Library/Cowpea%20%20Production%20guidelines%20for%20cowpea.pdf
Planting
Inter-row width depends on the growth habit of the variety being used. Upright types can be planted in 30cm to 90cm rows, semi-runners in 90cm to 150cm rows, and runners in 150cm to 200cm rows, depending on the rainfall. In-row spacing must not be more than 75cm to ensure a good plant population.
A planting depth of 5cm is best. Upright types need a plant population of at least 120 000 plants/ha for optimal production and 70 000 plants/ha in the case of semi-runner or runner types. https://www.farmersweekly.co.za/farm-basics/how-to-crop/growing-cowpeas/. For optimum yield, cowpeas should be planted late November to early December in lower rainfall areas of South Africa. The seed should be planted at 3 to 4 cm deep. The early-sown crops tend to have elongated internodes, are less erect, more vegetative and lower yielding than those sown at the optimum time. Date of planting manipulation is utilised by farmers for various reasons. The reasons include escape from periods of high pest load or to plant cowpea at such a time that harvesting of the crop would coincide with the period of dry weather.
Plant spacing and density
Three seeds are planted at 20 cm along the ridge spaced 75 cm apart (20 cm x 75 cm) representing 133 000 plants/ha for erect/semi-erect varieties and (50 cm x 75 cm; 60,000 plants/ha) for the spreading types but later thinned to two seedlings per hill, 1 week after germination. Seeding rate ranges from 25 to 30 kg of good and viable seeds per hectare in experimental stations. Commercial seeding rates would depend on plant spacing.
Fertilisation
Fertiliser application in cowpea production depends on anticipated yield and soil fertility. As a legume, cowpea fixes its own nitrogen, and does not need nitrogen fertiliser. Seed should be inoculated with the appropriate Rhizobium species for optimum nitrogen fixation, however nodules will generally form on cowpeas. Application of a phosphate fertiliser is usually beneficial. Cowpea can grow in a pH range of 5,6 to 6,5.
Irrigation
Cowpeas are usually grown under dryland rather than irrigated conditions.
Weed control
Annual grasses and some broadleaf weeds can be controlled by a pre-sowing application of herbicide. Row crop cultivation may be necessary with cowpeas, depending on the weed pressure, soil conditions, and rainfall. Replant tillage can assist greatly in reducing early weed pressure, and the use of cover crops. Striga gesnerioides and Alectra spp. are the principal parasitic weeds attacking cowpeas, particularly in the semiarid regions. The following three are the most common Striga species that are a pest to cowpea: S. hermonthica, S. asiatica and S. gesnerioides. The pest status is complex because the forms of parasitic weeds that are found on one species cannot germinate on another host plant. Careful observations and records are therefore necessary to clarify which crops are parasitized by which species. http://www.arc.agric.za/arcgci/Fact%20Sheets%20Library/Cowpea%20%20Production%20guidelines%20for%20cowpea.pdf
Common Pest and Diseases
Bacterial blight Xanthomonas campestris
Symptoms
Water-soaked spots on leaves which enlarge and become necrotic; spots may be surrounded by a zone of yellow discoloration; lesions coalesce and give plant a burned appearance; leaves that die remain attached to plant; circular, sunken, red-brown lesion may be present on pods; pod lesions may ooze during humid conditions
Cause
Caused by bacterium. Disease can be introduced by contaminated seed; bacteria overwinters in crop debris; disease emergence favoured by warm temperatures; spread is greatest during humid, wet weather conditions
Management
Plant only certified seed; plant resistant varieties; treat seeds with an appropriate antibiotic prior to planting to kill off bacteria; spray plants with an appropriate protective copper based fungicide before appearance of symptoms.
Anthracnose
Colletotrichum spp.
Symptoms
Tan to brown sunken lesions on leaves; lesions merging to girdle stems and petioles; lesions may become covered in pink spore masses during periods of wet weather
Cause
It is caused by fungi. Disease causes economically important losses to crops in Africa, Latin America and Asia
Management
The best method of controlling the fungus is to plant resistant varieties if available; plant only certified disease-free seed; practice good field sanitation such as removing crop debris from field after harvest to reduce levels of inoculum
Brown blotch
Colletotrichum capsici
Colletotrichum truncatum
Symptoms
Seeds not germinating; death of seedlings; post emergence symptoms include sunken oval lesions on stems, red-brown lesions on leaves, flowers aborting and/or mummified pods; severe defoliation can occur during prolonged periods of wet weather
Cause
It is caused by fungi. Disease particularly important in rainforest zone, southern Guinea savannas and the southernmost part of northern Guinea savannas
Management
The best method of controlling the fungus is to plant resistant varieties if available; plant only certified disease-free seed; practice good field sanitation such as removing crop debris from field after harvest to reduce levels of inoculum
Brown rust
Uromyces spp.
Symptoms
Raised brown to black pustules on both sides of leaves; wilting plants; drying leaves dropping from plant
Cause
Fungi. Major disease in parts of West Africa and in areas of medium elevation in East Africa
Management
Sprays of sulphur or potassium carbonate can help to control the disease
Cercospora and Pseudocercospora leaf spot
Cercospora canscens
Pseudocercospora cruenta
Symptoms
Chlorotic spots on upper surfaces of leaves; necrotic spots on leaves; masses of spores on lesions which resemble black mats on lower leaf surface; defoliation of plants; yellowing of leaves; circular, red lesions on leaves
Cause
Fungi. Pseudospora an important disease in China; both diseases occur in Africa
Management
Remove all crop residue from field after harvest; plant disease-free seed
Powdery mildew
Erisyphe polygani
Sphaerotheca fuliginea
Symptoms
White powdery fungal growth on upper surfaces of leaves; chlorotic or brown patches on leaves; leaves dropping from plant
Cause
Fungi. E. polygani occurs in all areas where cowpea is grown; S. fuliginea only reported in India
Management
Plant resistant varieties if available; use adequate plant spacing to avoid overcrowding and promote good air circulation around plants
Asochyta blight
Asochyta phaseolorum
Symptoms
Severe defoliation of plants; extensive lesions on stems and pods; if infection is severe then plants may be killed
Cause
Fungus. Major disease in Africa; disease transmitted by infected seed and from infected plant debris; secondary spread by rain splash and wind
Management
Plant disease-free seed; applications of appropriate foliar fungicides, where available, may help to control the disease
Soft stem rot
Pythium aphanidermatum
Symptoms
Gary to green water-soaked rot girdling stem; plant death; white mycelial growth on stem during high humidity
Cause
Fungus. Important in warm, humid tropical conditions of southern Guinea, West Central Africa and subtropical India
Management
Plant in well-draining soils or raised bed to reduce soil moisture content; solarizing soil can help reduce levels of inoculum in the soil; soil drenches or seed treatment with appropriate fungicides can help to control the disease
Rhizoctonia seedling blight
Rhizoctonia solani
Symptoms
Water-soaked sunken, red-brown lesions on hypocotyls (germinating shoot below seed leaves) and epicotyls (shoot above seed leaves); small, circular brown spots on leaves; large irregular lesions with zonate banding on leaves; lesions with water-soaked borders; leaves that look like they are covered in sand (sclerotia)
Cause
Fungus. Can cause complete destruction of canopy
Management
Crop rotation helps to reduce the build up of the fungus in the soil; reduce soil compaction; do not plant seeds too deep
Charcoal rot
Macrophomina phaseolina
Symptoms
Discoloration of stem at soil line; cankers on stem may spread upwards; leaves may wilt and drop from plant; numerous small black sclerota (fungal fruiting bodies) develop in affected tissues and can be used to diagnose the disease
Cause
Fungus. Fungus had a wide host range and affects beans, tobacco, soybean, pigeon pea and many other crops; disease is primarily spread via microsclerota in the soil
Management
Organic soil amendments such as the addition of manure or neemcake can be used to reduce levels of inocuum in the soil.
Southern blight
Sclerotium rolfsii
Symptoms
Sudden wilting of leaves; yellowing foliage; browning stem above and below soil; browning branches; stem may be covered with fan-like mycelial mat.
Cause
Fungus. Fungus can survive in soil for long periods; disease emergence favored by high temperatures, high humidity and acidic soil; disease found mainly in tropical and subtropical regions, including the southern United States.
Management
Remove infected plants; avoid overcrowding plants to promote air circulation; rotate crops with less susceptible plants; plow crop debris deep into soil; provide a barrier to infection by wrapping lower stems of plant with aluminum foil covering below ground portion of stem and 2-3 in above soil line
Fusarium wilt
Fusarium oxysporum
Symptoms
Stunted plant growth; yellowing, necrotic basal leaves; brown-red or black streaks on roots that coalesce as they mature; lesions may spread above the soil line
Cause
Fungus. Damage caused by the emergence of the disease is worsened by warm, compacted soils, limited soil moisture and poor soil fertility.
Management
Control relies on cultural practices e.g. do not plant in same area more than once in any 5-year span or treating seeds with an appropriate fungicide prior to planting
Aphids (Cowpea aphid, Pea aphid, etc.)
Aphis craccivora
Acyrthosiphon pisum
Symptoms
Small soft bodied insects on underside of leaves and/or stems of plant; usually green or yellow in colour, but may be pink, brown, red or black depending on species and host plant; if aphid infestation is heavy it may cause leaves to yellow and/or distorted, necrotic spots on leaves and/or stunted shoots; aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plants.
Cause
Insect. Distinguishing features include the presence of cornicles (tubular structures) which project backwards from the body of the aphid; will generally not move very quickly when disturbed
Management
If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control; check transplants for aphids before planting; use tolerant varieties if available; reflective mulches such as silver colored plastic can deter aphids from feeding on plants; sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; insecticides are generally only required to treat aphids if the infestation is very high – plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to use.
Armyworms (Beet armyworm, Western striped armyworm)
Spodoptera exigua
Spodoptera praefica
Symptoms
Singular, or closely grouped circular to irregularly shaped holes in foliage; heavy feeding by young larvae leads to skeletonized leaves; shallow, dry wounds on fruit; egg clusters of 50-150 eggs may be present on the leaves; egg clusters are covered in a whitish scale which gives the cluster a cottony or fuzzy appearance; young larvae are pale green to yellow in color while older larvae are generally darker green with a dark and light line running along the side of their body and a pink or yellow underside.
Cause
Insect. Insect can go through 3–5 generations a year.
Management
Organic methods of controlling armyworms include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis; there are chemicals available for commercial control but many that are available for the home garden do not provide adequate control of the larvae.
Corn earworm
Helicoverpa zea
Symptoms
Larvae damage leaves, buds, flowers, pods and beans; young caterpillars are cream-white in colour with a black head and black hairs; older larvae may be yellow-green to almost black in colour with fine white lines along their body and black spots at the base of hairs; eggs are laid singly on both upper and lower leaf surfaces and are initially creamy white but develop a brown-red ring after 24 hours and darken prior to hatching
Cause
Insect. Adult insect is a pale green to tan, medium sized moth; insect is also very damaging pests of corn; insect overwinters as pupae in the soil.
Management
Monitor plants for eggs and young larvae and also natural enemies that could be damaged by chemicals; Bacillus thuringiensis or Entrust SC may be applied to control insects on organically grown plants; appropriate chemical treatment may be required for control in commercial plantations
Mexican bean beetle
Epilachna varivestis
Symptoms
Irregular patches of feeding damage on underside of leaves which causes the top surface of the leaf to dry out, giving the leaves a lacy appearance; insect will also damage flowers and small pods; pods may be damaged so badly that they drop from the plant; adult insect is an orange-brown beetle with black spots; larvae are fat-bodied grubs which taper at the end and are in rows of conspicuous spines.
Cause
Insect. Beetles can decimate bean crops; beetles overwinter as adults and undergo 2-3 generations per year.
Management
Some bean varieties may be less attractive hosts for the beetle, e.g. snapbeans are preferred hosts over lima beans; early varieties may escape damage form beetles beetle populations can be reduced by remove overwintering sites such as brush and leaves on the ground; handpick larvae and adults; brush eggs from leaves and destroy; apply insecticidal soap to leaf undersides if infestation is heavy.
Root knot nematode
Meloidogyne spp.
Symptoms
Galls on roots which can be up to 3.3 cm (1 in) in diameter but are usually smaller; reduction in plant vigor; yellowing plants which wilt in hot weather.
Cause
Nematode. Galls can appear as quickly as a month prior to planting; nematodes prefer sandy soils and damage in areas of field or garden with this type of soil is most likely.
Management
Plant resistant varieties if nematodes are known to be present in the soil. Check roots of plants mid-season or sooner if symptoms indicate nematodes; solarizing soil can reduce nematode populations in the soil and levels of inoculum of many other pathogens. https://plantvillage.org/topics/cowpea/infos
Harvest
Cowpeas vary in growth habit. Erect or semi-erect types with short (<100 days) growth duration are grown mostly for grain. Semi-erect types and trailing plants have longer (>120 days) duration in and are grown primarily for forage. At maturity, leaves dry down but may not drop off completely. Cowpeas need to be harvested when seed moisture content is 14 to18%, depending on the consumer’s requirement. In cowpeas grown for vegetable purposes, the leaves are picked 4 weeks after planting, and this continues until the plants start to flower.
Harvesting method
Cowpea can be harvested using a harvester or by hand. The upright cultivars are easy to harvest by machine. Cowpea grown as a dried seed product can be directly combined, using a platform head or a row crop head. Adjustments to combine settings and sieve sizes should be made for the cowpea seed. Because the pods are relatively long, some will touch the ground or be close to it, making it important to run the grain table close to the ground. In the case of cowpeas grown for vegetable purposes, young leaves are mainly picked by hand; older leaves accumulate dust or get spattered with mud from raindrops if not harvested. In most cases, harvesting of cowpea should coincide with the onset of dry season when the dry pods can await harvesting for a week without spoilage. However, to avoid field weathering or shattering, dry pods should not be left in the field longer than 2 weeks after full pod maturity. Harvesting can be carried out manually (hand harvesting) or by using a combine harvester in the case of large-scale production.
Post-harvest handling
Sorting
Seed quality is important. Care in harvest and post-harvest handling allows to avoid cracked or split seed as such seeds which were allowed to dry on plant are harvested to ensure full maturity. Sorting is done to separate the broken seeds from full seeds.
Post-harvest handling
The leaves are dried to store for the dry season. Usually they are first steamed or boded, but not in all places. Sun-drying requires 1 to 3 days; storage is possible for up to a year because dried cooked leaves are not damaged by insects to the same extent as dried seeds. Excessive losses of P-carotene, vitamin C, and the amino acid lysine often occur in sun-dried leaves; however, these can be reduced by minimal cooking followed by drying in the shade.
Grading
The youngest leaves or tender shoots are gathered while in the distinctive green color phase of new growth. Young leaves are tender, usually higher in protein, and, lacking insect damage, often look more appealing. Older leaves accumulate dust or get spattered with mud from raindrops, while younger leaves would not need so much washing.
Packing
Buyers want the seeds cleaned and bagged, while others will take the grain in bulk form and clean it themselves. In case of sun drying, package in sacks and put into electrical dryers or spread on a concrete slab in order to reduce the moisture content to about 12%.
Storage
Insect pests can devastate cowpea during storage. There are storage insects that cause damage to the seed; it is therefore important to store seed in a protected place. A serious insect pest during storage is the cowpea weevil Callosobruchus maculatus, (Coleoptera: bruchidae). The rising popularity of organic produce lines has created interest in non-chemical disinfestation treatments; as the use of chemicals in controlling these insects is becoming a problem.
The storage life of cowpea depends on its moisture content before storage. The lower the moisture content, the better the quality of seeds in storage. The grain can be stored short term at around 12% moisture or less, with 8 to 9% recommended for long-term storage. Cowpea leaves are dried to store them for the dry season. Sun-dried leaves may store for up to a year because dried, cooked leaves are not damaged as much by insects as dried seeds. http://www.agriguide.org/index.php?what=agriguide&id=161&language=en
