Peanut (groundnut)

Scientific Clarification

The following are the crop details for Groundnuts

  • Scientific name: Arachis hypogaea
  • Local names: Njugu (Swahili)
  • Order: Fabales
  • Family: Fabaceae
  • Genus: Arachis



General Information

Groundnuts are small erect or trailing herbaceous legumes, about 15 to 60 cm high. The fruit is a pod with one to five seeds that develop underground within a needle-like structure called a peg.

The leaves are arranged in alternate pairs and have leaf-like attachments near the stalk. The groundnut plant produces yellow, orange, cream, or white flowers which produce 'pegs', characteristic floral structures which sink into the ground to grow the pod. The pods can reach up to 10 cm (4 in) in length and can contain between 1 and 5 seeds. The plant can reach 0.6 m (2 ft) in height depending on the variety and as an annual plant, survives only one growing season. 

The seeds are rich in oil (38-50%), protein, calcium, potassium, phosphorus, magnesium, and vitamins.

Groundnuts also have considerable medicinal value. They are reported to be useful in the treatment of diseases such as hemophilia, stomatitis, and diarrhea. 

In sub-Saharan Africa, groundnuts are a basic staple crop, cultivated mainly by small-scale farmers both as subsistence and as a cash crop. It is an important source of protein and other nutrients for poor rural communities. In Africa, groundnut yields are traditionally low, due to unreliable rains, little technology available to small-scale farmers, pest and disease occurrence, poor seed variety, and increased cultivation on marginal land (ICRISAT).

Groundnuts may also be referred to as peanut, monkeynut, or earth nut. Groundnuts originated in South America from southern Bolivia to north-western Argentina. The Portuguese took them from Brazil to West Africa and then to southwestern India in the 16th century. Africa is now regarded as a secondary center of diversity.




Groundnut Varieties in Kenya

There are two main varieties of groundnuts in Kenya:

  • Runner type
  • Bunch type

The runner is a large variety and it's highly preferred because of high yields, it matures in 90-100 days. Bunch varieties are small, tastier, and highly marketable, it matures in 60- 75 days.

Other varieties include Red Valencia, Red Oriata, Manipinta, Makulu Red, Bukene, Homa Bay, Texas Peanut, and Atika.

Red Valencia: This variety is easy to grow and produces two to five kernels per long pod. It’s slightly smaller in size and has a sweeter taste with papery red seed covers.




Climate Conditions, Soil, and Water Management

Groundnuts are grown in most tropical, subtropical, and temperate countries between 40°N and 40°S latitude, especially in Africa, Asia, North, and South America.  They are grown in the warm tropics and subtropics below 1500 m above sea level, and in temperate humid regions with sufficiently long warm summers. The optimum mean daily temperature to grow is 30°C and growth ceases at 15°C. Cool temperatures delay flowering. Groundnuts cannot stand frost. Between 500 and 600 mm of water reasonably well distributed through the growing season allows good production.

Groundnuts are drought-tolerant species and can withstand severe lack of water, but the yield is generally reduced. If harvesting conditions are wet, aflatoxins (severe poison produced by some fungi such as Aspergillus spp) may develop on the nuts. Aflatoxin contamination is a major hazard to human and animal health. When groundnuts are poorly dried and stored, they pick mold and dirt, which attracts fungi, that release aflatoxin chemicals that are dangerous to human health, especially the liver.

Pods develop underground and must be recovered at harvest, therefore crumbly, well-drained soils are preferred, but plants grow and develop adequately on heavier clay soils. For optimum growth, soil pH should be in the range of 5.5 to 6.5, though Bunch types tolerate more acidic conditions (pH 4.5) and some cultivars grow well in alkaline soils up to pH 8.5.




Uses

Most commercially grown peanuts are used for the extraction of their oil which is used in cooking. The by-product of oil extraction is a pressed cake which is used as animal feed and also in the production of peanut flour. Raw kernels are also commonly roasted and eaten as a snack food.

The vegetative residues from the crop are excellent forage.




Planting Procedure

Peanut is usually propagated from seed. Seeds should be planted in a well-prepared seedbed in soil that is loose and crumbly with no large clumps. The seedbed should be free from weeds which will compete with the peanut seedlings. Weeds may be removed by hand cultivating or through the use of an appropriate herbicide. Peanut seeds should be planted by hand to a depth of 3–5 cm (1–2 in). It is best to ridge the soil or use flat beds as this will make harvesting the peanuts easier.

After ploughing and harrowing to a fairly good tilth, ridges that are 80 cm apart with flattish tops, should be made so that two rows of nuts can be planted on each ridge. Seeds for planting should be well selected: they should be clean, well-filled, and without any blemishes. Seeds should be kept in their pods and shelled a few days before planting. Planting depth is like maize about 5 to 8 cm. Seed rate is 40 to 50 kg/ha depending on the size of the seeds.




Intercropping

They can be grown as a sole crop and also intercropped with maize, soybean, and cassava. It is also a good intercrop for upland rice, sorghum, okra, sugarcane, and sunflower.

In some areas, they are grown under perennial tree crops such as coconut, oil palm, or rubber. Groundnuts when used as intercrop for upland maize and planted along the contour reduce soil runoff. The plant also reduces the population of African bollworms because it serves as a hiding place for beneficial insects. There is an increase in the yield of groundnuts when intercropped with early-maturing pigeon peas.




Husbandry

To achieve maximum economic yields, weeds must be eliminated. Groundnuts are poor competitors with weeds during the early stages of growth. Weeding should be done early while at the same time earthing up the ridges to encourage "pegging" i.e. young nuts penetration through the soil. Once pegging has started, only hand weeding should be undertaken to avoid disturbing the young nuts or damaging the flowers. Clean weeding should be done in up to 6 weeks after which hand weeding should take over.

The only peculiar nutrient requirement is for calcium (Ca) in the podding zone. Calcium is absorbed directly by the pods if soil moisture is adequate. A shortage of Ca in that zone will result in empty pods (especially in Runner cultivars). The crop's needs for nitrogen should be satisfied with symbiotic fixation by strains of Rhizobium of the cowpea group, so nitrogen fertilizers are not generally required. 

In some areas of acid soils, lime is applied to raise the pH and supply Ca. Moisture stress during flowering or pod filling reduces yield therefore irrigation is important during those periods to minimize or eliminate the stress, and increase production and seed quality. Where yields are unsatisfactory (heavily eroded soils) an application of 200 kg/ha of rock phosphate is recommended.  




Harvesting

Bunch cultivars are harvested 85-100 days after sowing and Runner cultivars 110-130 days after sowing in the warm tropics. Dig a few plants up to see if the nuts are ready. The nuts should be brown on the outside, firm, and dry. Usually, at maturity the inside of the pods is grey and some rattling occurs when pods are shaken. Severe disease of foliage sometimes results in harvesting before seeds are fully mature.

Plants should be carefully dug out to avoid nuts breaking off and remaining in the ground. Dry for 2-3 days, then rip the pods from the bushes and place them on mats to dry for another 7-10 days to about 10% moisture. 

Shelling should be done by hand. Broken, dirty, or damaged nuts should be discarded as these will lower the quality and hence the selling price. When the groundnuts are poorly dried and stored, they pick mold and dirt, which attracts fungi, that release aflatoxin chemicals that are dangerous to human health, especially the liver. Nuts to be used as seeds the following year should not be shelled.




References

CABI Crop Protection Compendium. (2010). Arachis hypogaea (groundnut) datasheet. Available at: http://www.cabi.org/cpc/datasheet/6932. [Accessed 06 March 15]. Paid subscription required. Duke, J. A. (1983). Arachis hypogaea L. Handbook of Energy Crops. unpublished. Available at: http://www.hort.purdue.edu/newcrop/duke_energy/Arachis_hypogaea.html#Ecology. [Accessed 06 March 15]. Free to access. Kokalis-Burelle, N., Porter, D.M, Rodríguez-Kábana, R., Smith, D. H. & Subrahmanyam, P. (Eds.) (1997). Compendium of peanut diseases. Available at: http://www.apsnet.org/apsstore/shopapspress/Pages/4218X.aspx. Available for purchase from APS Press. Wright, S. (2012). Peanuts. University of Kentucky College of Agriculture Cooperative Extension Service. Available at: http://www.uky.edu/Ag/NewCrops/introsheets/peanuts.pdf. [Accessed 06 March 15]. Free to access.


Common Pests and Diseases

Diseases

Category : Fungal

Botrytis blight Botrytis cinerea

Symptoms
Numerous spots on upper surface of leaflets; entire plant or discrete parts may wilt and die; pods and stems become covered in fungal sclerotia.
Cause
Fungus
Comments
Disease emergence favors high moisture and high temperature; plants damaged by frost or other pathogens are particularly vulnerable to attack.
Management
Avoiding frost damage by planting early peanut varieties can help protect the plant from fungal colonization; application of appropriate foliar fungicides (e.g. benomyl), where available, can help to control the disease.

Charcoal rot Macrophomina phaseolina

Symptoms
Water soaked lesions on stems of seedlings close to soil line; lesions girdle stem and kill seedlings; lesions in similar area may be present in older plants; lesions are initially water-soaked but turn brown; if lesions girdle the stem, plant wilts and branches die; infections beginning in the roots cause leaves to turn yellow and wilt and causes stems to be blighted.
Cause
Fugnus
Comments
Fungus survives in crop debris in the soil; disease emergence is favored by high soil temperatures which cause plants to be water stressed and more susceptible to disease; fungus can survive for prolonged periods in dry soils but are killed in wet soil.
Management
Rotating crop with rice for a period of 3-4 years can reduce the level of oioculum in the soil; providing the plants with adequate irrigation and fertilization reduces susceptibility to the disease; there are currently no resistant varieties of peanut; frequent irrigation to wet soil reduces the incidence of the disease.

Cylindrocladium black rot Cylindrocladium crotalariae

Symptoms
Leaves on main stem turning chlorotic and wilting; entire plant wilts very rapidly when there is a period of water stress following high moisture; clusters of red-brown fungal bodies occur on on stems, pegs and pods; roots destroyed; roots blackened and shriveled.
Cause
Fungus
Comments
Crops planted early are more susceptible to the disease as they are often exposed to cooler temperatures and higher soil moisture; disease is seed transmitted and also can spread over long distances by wind.
Management
The most effective method to control the disease is to plant peanut varieties that have some resistance to the disease; rotation of crop with nonhost such as corn , cotton or tobacco may help to reduce inoculum in the soil; application of appropriate soil fumigants in heavily infested fields can help to control the disease.

Early leaf spot Cercospora arachidicola

Symptoms
Small chlorotic flecks on leaf petioles, stems and pegs which enlarge and turn dark in color; lesions on upper surface of leaves usually possess a yellow halo and are reddish brown on the underside of leaves.
Cause
Fungus
Comments
Disease emergence is favored by high humidity and warm temperatures; spread of the disease is promoted by pronlonged leaf wetness.
Management
If disease is present, a rotation away from peanut for a period of 2-3 years is advised but is insufficient to control the disease completely; peanut crop debris should be plowed into soil after harvest and any volunteers removed from the nonhost crop; fungicides should be applied with caution as they can exacerbate other foliar diseases where they are present.

Late leaf spot Cercospora personatum

Symptoms
Small chlorotic flecks on leaf petioles, stems and pegs which enlarge and turn dark in color; symptoms may be very similar or identical to early leaf spot and can only be differentiated by examination of conidia under a microscope.
Cause
Fungus
Comments
Disease emergence is favored by high humidity and warm temperatures; spread of the disease is promoted by pronlonged leaf wetness.
Management
If disease is present, a rotation away from peanut for a period of 2-3 years is advised but is insufficient to control the disease completely; peanut crop depris should be plowed into soil after harvest and any volunteers removed from the nonhost crop; fungicides should be applied with caution as they can exacerbate other foliar diseases where they are present.

Phyllostica leaf spot Phyllostica arachidis-hypogaea

Symptoms
Circular lesions with red-brown margins and light brown or tan centers on leaves; centers of lesions may dry out and drop from leaf resulting in a "shot-hole" appearance.
Cause
Fungus
Comments
Phyllostica leaf spot is known to occur in the U.S., India, China, Argentina, Thailand, the Philippenes, Pakistan, Zimbabwe, Niger and Burkino Faso.
Management
Disease is held in check by fungicides applied to control early or late leaf spot.

Rust Puccinia arachidis

Symptoms
Characteristic orange pustules on undersides of leaves which become covered in masses of red-brown spores; pustules may form on pods.
Cause
Fungus
Comments
Peanut rust is highly specific to peanut; disease emergence and spread is favored by warm temperatures followed by leaf wetness.
Management
Allow field to fallow for at least one month between successive peanut plantings; remove any volunteer peanut plants during fallowing to reduce inoculum; sprays of appropriate fungicides such as Bordeaux mixture can effectively control the disease; such fungicides are often also effective at controlling leaf spot.

Sclerotinia blight Sclerotinia minor

Symptoms
Tips of infected branches wilt or flag rapidly; early signs of infection include the presence of small water-soaked lesions at the base of the stems which turn yellow or bleached; leaves on infected branches turn chlorotic and then wither; fluffy white fungal growth may appear on infected tissues during periods of high humidity.
Cause
Fungus
Comments
Fungus can survive for prolonged periods in the soil, even in the absence of peanut; emergence of the disease in the peanut crop is favored by periods of cool weather, moist soil and high humidity.
Management
Plant seeds which are coated with protectants; avoid injuring plants with tools and/or machinery; application of appropriate fungicides can reduce crop losses when disease is present; avoid excessive irrigation during cool weather.

Southern stem rot Sclerotium rolfsii

Symptoms
Lateral branches or main stem yellowing and wilting; white fungal mat developing on the stem close to the soil line; white to brown spore containing structures developing from the fungal mats.
Cause
Fungus
Comments
Pathogen has a large host range and attacks many crops including sugar beets; disease favors dry soils which crack deeply, allowing the penetration of oxygen.
Management
Plow crop debris deeply into soil after harvest of crop; crop rotation of 3-4 years are very effective at reducing soil inoculum in the case of severe infestations; applications of appropriate fungicides can help suppress stem rot but care should be taken with selection as some pesticides (e.g. benomyl) are known to increase the severity of the the disease.

Verticillium wilt Verticillium spp.

Symptoms
Chlorosis of leaf margins; curling leaves; loss of leaf turgor; plants wilt and become stunted as the disease progresses; plants wilt rapidly during periods of water stress; vascular system becomes dicolored.
Cause
Fungi
Comments
Fungus can survive in the soil for several years; disease is spread to uninfested fields by movement of infested soil or contaminated tools and machinery; there are no peanut varieties known to have resistance to the disease.
Management
Irrigate plants frequently to reduce wilting of infected plants and allow them to reach maturity; eliminate weeds int he plantation which may allow inoculum to build up in the soil; remove and destroy infected crop residue after harvest to reduce inoculum in the field.

Web blotch (Phoma leaf spot) Phoma arachidicola

Symptoms
Circular, brown-black lesions on the upper surfaces of the leave; web or net-like brown lesions on leaves may form on leaves during periods of high humidity; as sisease progresses, lesions darken and develop a rough texture; lesions may cover entire leaf surface.
Cause
Fungus
Comments
Disease emergence is favored by cool, moist conditions and periods of prolonged leaf wetness.
Management
Remove and destroy infested crop debris to prevent build up of inoculum in soil; rotate crops away from peanut; foliar fungicide applications are largely ineffective if conditions are favorable for the disease.

Category : Viral

Stunt Peanut stunt virus (PSV)

Symptoms
Leaves curled and pale yellow to green; leaf petioles shortened; plants growth severely stunted; plants may produce very few pods if they have been infected early in the growing season.
Cause
Virus
Comments
PSV is transmitted by aphids; legumes such as white clover are the primary source of inoculum.
Management
Avoid planting peanut in close proximity to legumes such as clover; remove any infected plants from plantation to reduce inoculum.

Tomato spotted wilt virus & Peanut bud necrosis Tomato spotted wilt virus (TSWV)
Peanut bud necrosis virus (PBNV)

Symptoms
Chlorotic spots or mottled patterns on leaves; drooping leaflets during hot weather; necrosis of terminal buds; stunted growth; new leaflets are reduced in size and may be puckered with mosaic mottling.
Cause
Virus
Comments
Both viruses have an extremely wide host range and are transmitted by thrips vectors.
Management
Use high quality seed and use adequate plant spacings to avoid overcrowding; provide plants with adequate irrigation and fertilization to encourage the fast establishment of seedlings and growth of a close canopy which is unattractive to thrips vectors; intercropping peanut with sorghum or millet can reduce disease incidence.

Pests

Category : Insects

Armyworms Spodoptera spp.

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.

Thrips (Tobacco thrips) Frankliniella fusca
Frankliniella occidentalis
Thrips palmi

Symptoms
If population is high leaves may be distorted; leaves are covered in coarse stippling and may appear silvery; leaves speckled with black feces; insect is small (1.5 mm) and slender and best viewed using a hand lens; adult thrips are pale yellow to light brown and the nymphs are smaller and lighter in color.
Cause
Insect
Comments
Thrips transmit viruses to plants, including Tomato spotted wilt virus and Peanut bud necrosis virus.
Management
use adequate plant spacings to avoid overcrowding; provide plants with adequate irrigation and fertilization to encourage the fast establishment of seedlings and growth of a close canopy which is unattractive to thrips vectors.

Velvetbean Caterpillar Anticarsia gemmatalis

Symptoms
The larva causes damage to plant by feeding on leaves. The larva after hatching from egg starts feeding on leaves The first and second stage larva skeletonise the leaves by feeding only on soft parts. The later stage laraves consumes entire leaves. They will stripe the field just in four to seven days. The larvae may also feeds on tender stem, buds and pods.
Cause
Insect
Comments
Velvetbean caterpillars feeds on legume (like soybean, kudzu, velvetbean, horse beans, cowpea), cotton and several weeds. Generally moths lay eggs in mass under leaf surface.
Management
Encourage natural predators and parasites in the field; early or late planting of crops helps in escaping the insect attack; grow available resistant varieties; spray biocontrol agents like nuclear polyhedrosis virus (NPV) and the bacterium Bacillus thuringiensis (Bt). If the incidence is severe spray suitable insecticide.

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.

Category : Mites

Two-spotted spider mite Tetranychus urticae

Symptoms
Leaves stippled with yellow; leaves may appear bronzed; webbing covering leaves; mites may be visible as tiny moving dots on the webs or underside of leaves, best viewed using a hand lens; usually not spotted until there are visible symptoms on the plant; leaves turn yellow and may drop from plant.
Cause
Arachnid
Comments
Spider mites thrive in dusty conditions; water-stressed plants are more susceptible to attack.
Management
Spraying plants with a strong jet of water can help reduce buildup of spider mite populations; if mites become problematic apply insecticidal soap to plants; certain chemical insecticides may actually increase mite populations by killing off natural enemies and promoting mite reproduction.
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