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Green gram
Scientific name:
Vigna radiata
Order/Family:
Fabales: Fabaceae
Local names:
Pojo (Swahili)
Importance:
medium
Common names:
Mung bean
Pests and Diseases (clicking takes you to the pest and disease pages):
Bacterial blight, Rust, Yellow mosaic virus, Bean flies, Foliage beetles, Pod borers, Bugs, Flower thrips, Cowpea seed weevil
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 Geographical distribution indicated in red
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General Information on Green GramAgronomic AspectsStorageInformation on Major Gram DiseasesInformation on Major Gram PestsInformation Source LinksContact links
Grams are annual legume crops grown for their seed. Grams could be green, black or yellow in colour. The green grams are the most commonly grown in Kenya. Grams are native crops of India. Often called green gram or golden, it is cultivated in several countries of Asia, Africa, and the Americas. The dried beans are prepared by cooking or milling. They are eaten whole or split. The seeds or the flour may enter a variety of dishes like soups, porridge, snacks, bread, noodles and even ice cream. Green gram also produces great sprouts, which can be sold in health food shops or eaten at home. Crop residues of V. radiata are a useful fodder. Green gram is sometimes specifically grown for hay, green manure or as a cover crop.
Climatic conditions, soil and water management
Green grams grow best at an altitude of 0-1600 m above sea level and under warm climatic conditions (28 to 30°C). They are well adapted to red sandy loam soils, but also do reasonably well on not too exhausted sandy soils. Green grams are not tolerant of wet, poorly drained soils. They are drought tolerant and will give reasonable yields with as little as 650 mm of yearly rainfall. Heavy rainfall results in increased vegetative growth with reduced pod setting and development. Propagation and Planting
Avoid planting green gram for more than one season because toxic residues and disease organisms from the previous green gram crop may affect the following crop adversely. Land should be prepared to a medium tilth before planting and early enough so that planting can start immediately after the rain starts. When using oxen plough for planting, place the seed at the side of the furrow.
Propagation is by seed. There is no seed dormancy. Seeds may sprout in the pod under very humid conditions. In areas with higher rainfall, it is recommended to grow green grams on raised beds. Prepare the beds, raised about 20 cm and spaced 1 m from the centre of one bed to the centre of the next. Sow seeds on raised beds in two rows per bed, spaced 45 cm apart.
Green grams will respond to fertiliser or manure application but will normally give satisfactory results if grown on relatively good soil.
Green gram is grown mainly on smallholdings, often as mixed crops or intercrops. Associated crops are usually of longer duration than green gram (sugar-cane, cotton, sorghum). To make use of a short cropping period, short-duration green gram is often relay-cropped.
Varieties
Green grams usually mature in 60 to 90 days. The early maturing varieties can often produce before drought destroys many bean species. Two varieties can be distinguished in Kenya:
| Variety | Maturity Days | Potential yield Bags/ha | Remarks |
| "KUR 22" | "80-90" | "11-14" |
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| KVR 26 | 60-65 | 14-17 |
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Husbandry
With the newer cultivars ripening in 60 to 75 days, maximum yields are obtained at plant densities of 300 to 400,000 plants per ha. The later-maturing traditional cultivars generally need wider spacing. Usually no fertilisers are applied to green gram. Over the centuries, green gram's adaptation to stable performance in marginal environments has resulted in a low yield potential, which limits responsiveness to better environments and improved cultural practices. However, if planted in heavily eroded soil gram will benefit from any kind of manure or compost. Grams planted at the end of the long rains are normally intercropped into other major crop. In Meru, Kenya, green gram is a preferred intercrop for millet, each said to protect the other against diseases and pests. If grams are intercropped with maize, the maize spacing is the same as in pure stand, but the grams are interplanted mid-way between the maize rows.
Early weeding is recommended. First weeding should be done just after emergence and second weeding just before flowering.
Harvesting
Harvesting is generally by two to five hand-pickings at weekly intervals and is the most expensive single operation in growing green gram. Short-duration cultivars, which ripen more uniformly, may be processed as whole plants on small rice threshers. Cultivars differ markedly in harvesting efficiency, depending on position (above or within canopy) and size of pods. Harvesting before the maturity of crop, usually result in lower yields, higher proportion of immature seeds, poor grain quality and more chances of infestation during storage. Delay in harvesting results in shattering of pods and other losses caused by pests. In Kenya, harvesting when 95% of pods have turned black is recommended. The whole plant can then be uprooted and dried for about 2 days, then threshed and winnowed. Harvesting during adverse weather condition i.e. rains and overcast weather should be avoided. Such weather is conducice to fungal infection.
The harvested bundles should be kept in one direction in order to ascertain efficient threshing. They should be stacked in a dry, clean place in cubical way to facilitate circulation of the air around. Grams must be dry before storage. Like most pulses moisture content at storage should not be above 13%. Grams are very susceptible to bruchid (bean weevil) attack and are best stored immediately after sun drying either in airtight drums tins or gunny bags and be kept in a clean, ventilated place. Mixing seed with ash is effective against bruchids, also treatment with sunflower oil or mixing with neem leaves is said to be effective against storage pests. Proper drying of grains is very important to prevent the growth of fungi and contamination with aflatoxins. Infected grains should be separated from sound grains to avoid aflatoxin contamination.
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| Bacterial blight on beans. Symptoms are similar on green grams. |
| © Sheppard JW (Courtesy of EcoPort, www.ecoport.org) |
Leaf spots first appear as small, water-soaked or light-green areas on leaflets. They later become dry and brown. The spots may join to affect much of leaf surface eventually killing the leaflet. Similar water-soaked spots develop on pods. The spot margin is a shade of red. Severely diseased pods shrivel. In humid weather, a yellowish crust of the blight bacteria covers the spot surface.
What to do:
- Cultural practices are important in controlling bean blights. Eliminate weeds, volunteer beans and other potential hosts of bean blight, as this will reduce disease incidence.
- Good weed control will also improve aeration around the crop so that the plants dry faster, this will reduce the chances for bacterial spread and infection.
- The bacteria are readily spread by water, and walking or working in the field while plants are wet will splash the bacteria and create wounds. Therefore avoid field operations when it is wet.
- A rotation of at least 2 years between bean crops will give time for the bacteria population to decline in the debris.
- Deep ploughing will also encourage the breakdown of infected plant debris.
- The incidence of bean blight can also be reduced if beans are grown with maize rather than in a monoculture.
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| Powdery mildew of pea Erysiphe polygoni |
| © AgrEvo (Reproduced from the Crop Protection Compendium, 2005 Edition. © CAB International, Wallingford, UK, 2005) |
White powdery patches appear on leaves and other green parts, which later become dull coloured. These patches gradually increase in size and become circular covering the lower surface. When the infection is severe, both the surfaces of the leaves are completely covered by whitish powdery growth. Severely affected parts get shrivelled and distorted. In severe infections, foliage becomes yellow causing premature defoliation. The disease also creates forced maturity of the infected plants which results in heavy yield losses. The fungal agent (pathogen) has a wide host range and survives on various hosts in off-season. It is spread by wind and water splash.
What to do:
- Plant resistant varieties, if available
- Plant early
- Remove weeds
- Practice a good field sanitation
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| Rust on lower leaf surface of French beans. Symptoms are similar on green grams. |
| © A. M. Varela, icipe |
The disease appears as circular reddish brown pustules (blisters) which appear more commonly on the underside of the leaves, less abundant on pods and sparingly on stems. When leaves are severely infected, both the surfaces are fully covered by rust pustules. Shrivelling of pods is followed by defoliation resulting in yield losses. Long distance spread of rust is by wind. Plant to plant spread is by farm tools, and moving bodies within the crop.
What to do:
- Plant resistant varieties, if available
- Avoid continuous cropping with legumes
- Practice crop rotation with non-legumes such as cereals
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| Anthracnose (Colletotrichum lindemuthanium) on beans pod. Symptoms are similar on green grams. |
| © Jim Sheppard (Courtesy of EcoPort, www.ecoport.org) |
It attacks all above ground parts of the plant. It does most serious damage on pods. Affected pods have brownish sunken spots, which under humid conditions are covered with a pink spore mass. Infected seeds become discoloured (brownish black).
What to do:
- Plant certified disease-free seeds
- Plant resistant varieties, where available
- Practice crop rotation with non-legumes such as cereals
Damping-off diseases (Pythium spp., Fusarium spp., Rhizoctonia solani)
They are caused by a complex of fungi. They cause rotting of seeds before emergence and seedlings after emergence from the soil. Affected fields appear patchy. They are favoured by wet, cool weather.
What to do:
- Use certified disease-free seeds
- Practice proper irrigation
- Treat seeds with hot-water, if necessary. For more information on hot-water seed treatment click here..
Gram yellow mosaic virus
Initially mild scattered yellow spots appear on young leaves. The spots gradually increase in size and ultimately some leaves turn completely yellow. Infected leaves also show necrotic symptoms. Diseased plants are stunted, mature late and produce very few flowers and pods. Pods of infected plants are reduced in size and turn yellow in colour. The virus is transmitted by whiteflies (Bemisia tabaci).
What to do:
- Use certified disease-free seeds
- Plant tolerant/resistant varieties
- Weed properly
- Control whiteflies
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| Bean fly on French beans |
| © A.M. Varela, icipe |
Bean flies can cause serious stand reductions at the seedling stage. Adults are tiny black flies with transparent wings, about 1/4 the size of a common housefly. Bean flies lay eggs in punctures of leaves near the petiole. The small white maggots feed inside the main stem just above the soil line. Pupation occurs inside the stem. The life cycle may be completed rapidly, often in less than 2 weeks.
Seedlings attacked by beanflies may wilt or die. Leaves of older plants may be yellow and stunted. Stems are thicker than normal and cracked lengthwise just above the soil. Maggot feeding facilitates the entry of disease-causing microorganisms leading to secondary infections. In cases of heavy infestation, many plants die. Bean flies are important only during the seedling stage (up to 4 weeks after germination).
What to do:
Various cultural practices help to minimise reduce damage by beanflies:
- Ridging the plants 2-3 weeks after germination helps to cover the adventitious roots produced by plants damaged by beanflies (these roots grow directly from stems and/or leaves). The soil support prevents lodging and improves the survival of the damaged plants.
- Plant after green manure crop
- Practice crop rotation with non-legumes such cereals
- Mulch with rice straw. The mulch covers the seed leaves (cotyledons) making them inaccessible for egg laying.
- Avoid late plantings since infestations of bean fly are heavier then.
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| Black legume aphid / Groundnut aphid (Aphis craccivora) is a relatively small aphid. Immatures are slightly dusted with wax, adults without wax. Apterae are 1.4-2.2 mm long. Alatae (winged form) 1.4-2.1 mm. |
| © Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org |
Aphids, mainly the legume aphid (Aphis craccivora) are relative small aphids. Immatures are slightly dusted with wax, adults without wax. Apterae are 1.4 to 2.2 mm long. Alatae (winged form) 1.4 to 2.1 mm. They feed on young plants, leaflets, stem and pods of green gram. Attacked young leaves become twisted. Excretion of honeydew leads to growth of sooty mold. Aphids are also vectors of virus diseases.
What to do:
Management measures include:
- Plant early
- Cultivate clean
- Avoid excess use of nitrogen
- Conserve natural enemies.
Foliage beetles (Ootheca spp.)
Foliage beetles have been reported as pests of green grams in West Africa. They are a threat, when present in large numbers since they can defoliate young plants.
What to do:
- Practice post harvest tillage to expose the grubs in the soil to the sun heat and to predators
- Rotate beans with non-host plants such as maize or sunflower to break the development cycle of the pest
- Delay sowing, where practicable, to allow the crop to escape from high populations
- Apply neem; it has been shown to reduce flea beetle numbers and damage
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| African bollworm on french beans - Fully grown caterpillars are 3-4cm long. |
| © A.M. Varela, icipe |
Pod borers such as the African bollworm (Helicoverpa armiguera), the legume pod borer (Maruca vitrata), and the lima bean pod borer (Etiella zinckenella) can cause serious economic damage. Young caterpillars of the African bollworm feed on leaves by scraping tissue for short time, and then bore into the pods and feed on the seeds with their heads thrust inside and most part of the body outside. The entry hole is large and circular. They also cause significant damage to flower buds and flowers.
Caterpillars of the legume pod borer (Maruca vitrata) are dull to yellow-white and often reach a length of 18 mm. Each segment has dark spots that form a distinct series along the length of the body. The head is dark brown to black. Caterpillars web together leaves, buds and pods and feed inside the web. Flowers attacked may be discoloured and have damaged or missing reproductive parts. Damage by this caterpillar also results in flower bud shedding and reduced pod production. Damaged pods have small, darkened entry holes on the surface.
Young caterpillars of the lima bean pod borer are green, later turning red. They feed inside the pod reaching a length of 14 mm. They are generally found in maturing and dried pods. Faeces in the form of granules are found inside the damaging pods.
Once the caterpillars have entered the pods they are difficult to control and by then they have caused damage.
What to do:
- Biopesticides such as Bt or neem products usually give good control of pod borers, provided they are applied to the young caterpillars before they enter into the pods.
- Monitor the crops frequently as there is only a brief period from hatching to entering buds or pods
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| Spiny brown bugs measure about 1cm in length. |
| © A.M. Varela, icipe |
Pod sucking bugs such as giant coreid bugs (Anoplocnemis curvipes), spiny brown bugs (Clavigralla spp.), green stink bugs(Nezara viridula, Acrosternum acutum), and Riptortus bugs (Riptortus spp) are the most important pests of green gram at the podding stage.
They suck sap from pods and seeds and cause various levels of damage depending on the stage of growth of seeds at the time of attack. Feeding may cause necrosis, pod malformation, premature drying, shrivelling of seeds, loss of germination ability, and formation of empty pods. Bugs are difficult to control since they usually feed on a wide range of crops and are very mobile.
What to do:
- Bugs can be collected by hand regularly and killed, especially during flowering and pod formation
- Conserve natural anemies such as assassin bugs, spiders, praying mantises and ants. These are important natural enemies of bugs. They kill or deter bugs. Conserve and attract predatory natural enemies to your crop by planting flowering plants. For more information on natural enemies click here
- Neem products are reported to repel bugs. If necessary spraying should be done in the morning when the immature stages are exposed
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| The Western flower thrips (Frankliniella occidentalis). Close-up, very much enlarged. Real size (0.9 to 1.1 mm) |
| © M. Billah, icipe |
It may feed on petioles and leaves, but prefer flowers. Attacked petioles and leaves have tiny holes surrounded by discoloured areas. Affected flowers are brown, dried, or completely distorted. The flowers drop prematurely. Thrips also feed on pollen leading to decrease in pollination and seed set. Pod production is low and pods are deformed.
What to do:
- Plough and harrow before planting. It can reduce subsequent thrips attacks by killing pupae in the soil
- Conserve natural enemies. Natural enemies, particularly, predators are important in natural control of thrips. Main natural enemies include predatory bugs (Orius spp. and Anthocoris spp.) and predatory thrips
- Spray with biopesticides (e.g. Spinosad), if infestation is severe
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| Cowpea seed weevil on cowpea |
| © Peter Credland, Reproduced from CABI 2006 |
It is a serious storage insect, which can destroy whole seed-lots.
What to do:
- Dry grains to moisture level below 13%
- Store grains in dry, well ventilated areas
- AIC (2002). Field Crops Technical Handbook.
- Adamu, R. S., Dike, M. C., Akpa, A. D. (2001). Insect fauna associated with greengram (Vigna radiata (L.) Wilc.) in the Northern Guinea Savanna of Nigeria. Journal of Sustainable Agriculture and the Environment, (Vol. 3) (No. 2) 331-336.
- CAB International (2005). Crop Protection Compendium, 2005 edition. Wallingford, UK www.cabi.org
- From ECHO's seedbank. Green Gram or Mung Bean (Vigna radiata). By Bob Hargrave, ECHO Staff. http://food-security.info/food-security.info/pdf
- Insect Pest Management in Moong. Integrated Pest Management. http://www.jnkvv.nic.in/IPM%20Project/insect-moong.html
- JNKVV, Madhya Pradesh, India: Diseases of green grams. http://www.jnkvv.nic.in/
- Kenya Agricultural Research Institute. KARI. Improved Green Gram Production. http://www.kari.org/InfoBrochures/GreenGramProd.htm
- Lost Crops of Africa: Volume II: Vegetables (2006) Development, Security, and Cooperation (DSC). Online read-only: The National Academy Press: www.nap.edu/catalog/11763.html
- Post harvest profile of green gram. Government of India, Ministry of Agriculture (Department of Agriculture and Cooperation) Directorate of Marketing and inspection. Branch Head Office. Nagpur - 440001. MRPC-76. http://agmarknet.nic.in/Greengram_profile.pdf
- Publications and Fact Sheets on Mungbean. AVRDC Extension Materials. http://www.avrdc.org/LC/mungbean/home.html
