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Cowpea

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Description

Cowpea, Vigna unguiculata, is a climbing annual in the family Fabaceae grown for its edible seeds and pods. The cowpea plant is usually erect and possess ribbed stems and smooth trifoliate leaves which are arranged alternately on the stems. The plant produces clusters of flowers at the end of a peduncle (flower stalk) and 2–3 seed pods per peduncle. The seed pods are smooth, cylindrical and curved, reaching up to 35 cm (10 in) in length, with distinctive coloration, usually green, purple or yellow. As the seeds reach maturity the pod changes color to tan or brown. The seeds can be white, cream, green, red brown or black in color or be a mottled combination. The seed may also possess an ‘eye’ where a lighter color is surrounded by one that is darker. Cowpea can reach in excess of 80 cm (31.5 in) in height and, as an annual plant, lives for only one growing season before harvest. Cowpea may also be referred to as black-eyed pea, southern pea, crowder pea or field pea and originates from Africa.


Uses

Cowpea is an important grain legume in Africa, parts of the Americas and in Asia. The seeds can be consumed fresh along with the pods and leaves as a vegetable. Dried seeds are consumed after cooking. The plant can be used as a forage or for hay or silage.


Propagation

Basic requirements Cowpea is a warm season crop and thrives in hot, moist conditions. Cowpeas have similar growth requirements to soybeans and should not be planted until until after the last frost and only when the soil temperature has reached 18.3°C (65°F) to prevent seeds rotting in the ground. The plants will be killed by frost. Cowpeas can be planted in a wide range of soils, from acidic (to pH 4) to neutral, as long as they are well-draining but the plants are not well adapted to alkaline soil. For best results,plant cowpeas in a well draining sandy loam with a pH between 5.5 and 6.5 in an area that receives full sun. Cowpeas are drought resistant and very heat tolerant which means they can be grown successfully in many areas. Planting Cowpeas should be direct seeded when the soil temperature is consistently above 18.3°C (65°F). Seeds should be sown to a depth of 2.5–5.0 cm (1–2 in) at a density of 4-8 plants per foot of row. An additional 76 cm (30 in) should be left between rows. Seeds germinate quickly and the plants should produce pods in approximately 60 days. General care and maintenance Cowpea is fast growing and should quickly suppress any competing weeds. Some perennial grass species may colonize the spaces between rows and should be removed by cultivation. Cowpeas can grow in poor quality soils and do not require the addition of nitrogen fertilizers. In addition, the plants can grow a taproot which is often in excess of 2.4 m (8 ft) which allows the plant to access moisture deep down in the soil. This makes cowpea extremely resistant to drought, requiring little or no irrigation after the plants have become established.


References

CABI Crop Protection Compendium. (2008). Vigna unguiculata datasheet. Available at: http://www.cabi.org/cpc/datasheet/56377. [Accessed 14 November 14]. Paid subscription required. Schwartz, H. F., Steadman, J. R., Hall, R. & Forster, R. L. (2005) Compendium of Bean Diseases. Available at: http://www.apsnet.org/apsstore/shopapspress/Pages/43275.aspx. Available for purchase from APS Press. Quinn, J. (2014). Cowpea. A Versatile Legume for Hot, Dry Conditions. Jefferson Institute. Available at: http://www.hort.purdue.edu/newcrop/articles/ji-cowpea.html. [Accessed 14 November 14]. Free to access.


Common Pests and Diseases

Diseases

Category : Fungal

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
Fungi
Comments
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

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
Comments
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

Brown rust Uromyces spp.

Symptoms
Raised brown to black pustules on both sides of leaves; wilting plants; drying leaves dropping from plant
Cause
Fungi
Comments
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
Comments
Pseudospora an important disease in China; both diseases occur in Africa
Management
Remove all crop residue from field after harvest; plant disease-free seed

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
Comments
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

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
Comments
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

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
Comments
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

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
Comments
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

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
Comments
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

Category : Bacterial

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
Bacterium
Comments
Disease can be introduced by contaminated seed; bacteria overwinters in crop debris; disease emergence favored 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

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
Fungi
Comments
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

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
Comments
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

Pests

Category : Insects

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 color, 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
Comments
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
Comments
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 color with a black head and black hairs; older larvae may be yellow-green to almost black in color 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
Comments
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
Comments
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

Category : Nematodes

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
Comments
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
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