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Root-knot nematodes
Scientific name:
Meloidogyne spp. (M. incognita, M. hapla, M. javanica, M. arenaria)
Order/Family:
Tylenchida: Meloidogynidae
Local names:
Eelworms
Type:
disease (nematodes)
Host plants:
Bananas  Beans  Carrot  Citrus plants  Coffee  Cotton  Cowpea  Cucumber  Eggplant  Groundnut  Okra  Papaya  Passion fruit  Peas  Peppers  Pigeon pea  Pineapple  Potato   Rice  Soybean  Sweet potato  Tea  Tomato  Watermelon  Dolichos  
General Information on Pest and Damage
Geographical distribution
Geographical Distribution of Root-knot nematodes in Africa (red marked)
Introduction
The root knot nematode species, M. incognita, is the most widespread and probably the most serious plant parasitic nematode pest of tropical and subtropical regions throughout the world. It occurs as a pest on a very wide range of crops.

Damage
Affected plants appear in patches. Estimates of vegetable crop losses due to Meloidogyne species, mainly M. incognita and M. javanica, have ranged from 17 to 20% for aubergine (Solanum melongena), 18 to 33% for melon and 24 to 38% for tomato.
Losses of potatoes due to Meloidogyne species, mainly M. incognita, are estimated at 25% or more.

Host range
Root-knot nematodes affect a wide range of crops, particularly vegetables. M. incognita is a major economic pest of food legumes in the tropics and subtropics. Common bean (Phaseolus vulgaris) is very badly damaged by Meloidogyne species in the tropics. Cowpea (Vigna unguiculata) is another very susceptible host crop of M. incognita. Many crops grown as vegetables are susceptible to the nematode particularly tomato, aubergine, okra, cucumber, melon, carrot, gourds, lettuce and peppers. Table I shows susceptibility of various commonly grown crops to root-knot nematodes.

Table 1. Crop susceptibility to root-knot nematodes (after AfFOResT)
Susceptible Tolerant Resistant
Bambara nut Brassicas Cassava
Beans Chilli pepper Garlic
Beetroot Radish Leek
Carrot Sweet potato Maize
Celery Turnip Millet
Cowpea Rhodes grass
Cucumber Sesame
Eggplant Sorghum
Gourd Sudan grass
Irish potato Sweet corn
Lettuce
Melon
Okra
Parsley
Peas
Pumpkin
Squash
Sweet pepper
Swiss chard
Tomato

(Source: Dobson et al. 2002)

Root-knot nematodes
Root-knot nematodes (Meloidogyne incognita / M. javanica) Roots of severely attacked (left) and healthy plant (right). Affected plants are normally stunted and eventually wilt and die. The most characteristic symptom is formation of root galls (knots) and these can be seen with the naked eye. Affected roots rot.
© A. M. Varela, icipe
Symptoms
Affected plants are stunted and yellow and have a tendency to wilt in hot weather. Very heavily infested plants are killed. Affected plants appear in patches. If infested plants are pulled from the soil, the roots are severely distorted, swollen and have lumps known as galls or root knots. The galls range in size from smaller than a pinhead to 25 mm or more in diameter.

Affected plant stages
Flowering stage, fruiting stage, seedling stage and vegetative growing stage.

Affected plant parts
Leaves, roots and whole plant.

Symptoms on affected plant part
Leaves: wilting.
Roots: galls; reduced root system; swollen roots.
Whole plant: dwarfing; wilting
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Biology and Ecology of Root-knot Nematodes
There are four species of root-knot nematodes (M. arenaria, M. hapla, M. incognita) and M. javanica) that are capable of attacking vegetables. These species occur in Kenya (National Horticultural Research Station, 1984) and are particularly serious in irrigated fields. Important environmental factors that influence development of Meloidogyne are moist soils and relatively warm temperatures. Some plant penetration by root-knot nematodes occurs between 10 and 35°C, with the optimum at about 27°C depending on the species. No eggs are laid at temperatures lower than 14.2 or higher than 31.7°C. Under average conditions a female produces 300 to 800 eggs. A new generation can arise within 25 days, but under less favourable conditions, the time may be prolonged to 30 to 40 days. All species, with exception of M. hapla are killed by freezing.

Root-knot nematodes measure about 0.5 mm to 1.5 mm in length.

Juveniles (young nematodes) penetrate the root tips and occasionally invade roots in the zone of root elongation. Invaded nematodes initiate the development of giant cells in the root tissues and galling of roots occurs.

Root knot nematodes are soil inhabitants. They are spread by transplanting infested seedlings, or from soil washed down slopes or sticking to farm implements and farm workers. They may also be spread by irrigation water.

The disease is most serious on light, sandy soils and in furrow irrigated areas. Attack by nematodes may greatly increase the severity of bacterial, Fusarium and Verticillium wilt diseases

Conditions that favour development:
  • Infected volunteer plants
  • Monocultures
  • Weeds in fields
  • Warm temperatures and moist but well-aerated sandy soils
  • Continuous growing of susceptible crops (no rotation)
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Pest and Disease Management
Pest and disease management: General illustration of the concept of infonet-biovision
This illustration shows the methods promoted on infonet-biovision. The methods shown at the top have a long-term effect, while methods shown at the bottom have a short-term effect. In organic farming systems, methods with a long-term effect are the basis of crop production and should be of preference. On the other hand methods with a short-term effect should be used in emergencies only. On infonet we do not promote synthetic pesticides.

Further below you find concrete preventive and curative methods against Root-knot nematodes.
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Cultural practices

Prevention and control
  • Do not locate seedbeds where vegetables have been grown previously. After preparation of the seedbed, burn the topsoil using dry leaves or other waste plant material.
  • Solarise seedbeds if possible.
  • Use biofumigation where possible (for more information on biofumigation click here). Different mustards (e.g. Brassica juncea var. integrifoliaorBrassica juncea var. juncea) should be used as intercrop on infested fields. As soon as mustards are flowering they are mulched and incorporated into the soil. While incorporated plant parts are decomposing in a moist soil, nematicidal compounds of this decomposing process do kill nematodes. Two weeks after incorporating plant material into the soil a new crop can be planted or sown.
  • Maintain high levels of organic matter (manure and compost) in the soil.
  • Incorporate neem cake powder into the soil if it is available.
  • Fields should be ploughed deep and the followed by a dry fallow.
  • Uproot entire plants from the field after harvest and destroy crop debris.

Crop rotation
Rotate with onions, baby corn, sweet corn, maize, millet, sorghum, sesame, cassava or Sudan grass.

A rotation system called "STRong" is recommended for management of root-knot nematodes. The system was developed by, African Farmers' Organic Research and Training (AfFOResT), a NGO in Zimbabwe. It involves planting in rotation of a susceptible crop (e.g. tomatoes), followed by a tolerant crop (e.g. cabbage) and then a resistant crop (e.g. onions) before a return to a susceptible crop (e.g. tomatoes). Crop susceptibility of various commonly crops is given in Table 1.

Use trap crops such as marigold (Tagetes spp.) and Indian mustard. (A trap crop is a crop planted to attract a pest and is then destroyed together with the pest). Mixed cropping with marigold can also minimise root-knot nematode damage.

Resistant varieties
Use resistant tomato varieties (e.g. 'Caracas', 'Kentom', 'Meru', 'Piersol', 'Roma VFN', 'Tengeru 97', 'Zest F1', 'Star 9001', 'Star 9003'). Tomato varieties carrying 'VFN' label are tolerant to root-knot nematodes. Most of these varieties are commercially available in the region.

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Information Source Links
  • Additional information about nematodes: Genome Sequencing Center: www.nematode.net
  • Beije C.M, Kanyagia S.T., Muriuki S.J.N., Otieno E.A., Seif A.A. and Whittle A.M. (1984). Horticultural Crops Protection Handbook. National Horticultural Research Station.
  • Crop Protection Compendium, 2005 Edition. © CAB International, Wallingford, UK, 2005 www.cabi.org
  • Dobson, H., Cooper, J., Manyangarirwa, W., Karuma, J., Chiimba, W. (2002). Integrated Vegetable Pest Management. Natural Resources Institute, University of Greenwich, UK. ISBN: 0-85954-536-9
  • OISAT. Organisation for Non-Chemical Pest Management in the Tropics www.oisat.org
  • Varela, A.M., Seif, A.A., and Löhr, B. (2003). A Guide to IPM in Tomato Production in Eastern and Southern Africa. ICIPE, Nairobi, Kenya. ISBN: 92 9064 149 5
  • Varela, A.M.and Seif, A. (2004). A Guide to IPM and Hygiene Standards in Okra Production in Kenya. ICIPE, Nairobi, Kenya. www.icipe.org
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Okra roots damaged by root-knot nematodes. Note gall or root-knots (left) and healthy roots (right).
© A.M. Varela, icipe
Clones
Bud cuttings from different varieties
Crop rotation
Crop rotation is the practice of growing different crops in succession on the same land.
Transplanting
Transplanting is the planting of uprooted seedlings grown in seedbeds or in nurseries, in a permanent location where they will continue to grow
lateral
of or pertaining to the side; situated at, proceeding from, or directed to a side: a lateral view.
Diameter
Thickness or width.
Cucurbits
Cucurbitaceae is a plant family commonly known as melons, gourds or cucurbits and includes crops like cucumbers, squashes (including pumpkins), luffas, melons and watermelons. The family is predominantly distributed around the tropics, where those with edible fruits were amongst the earliest cultivated plants in both the Old and New Worlds.
Farmyard manure
Droppings and beddings of farm animals, usually of cattle.
Exception
Permission granted to an operator by a certification body to be excluded from the need to comply with normal requirements of the standards. Exceptions are granted on the basis of clear criteria, with clear justification and for a limited time period only.
Brassicaceae
Brassicaceae or Cruciferae, also known as the crucifers, the mustard family or cabbage family is a family of flowering plants. The name Brassicaceae is derived from the included genus Brassica. The family contains well-known species such as Brassica oleracea (cabbage, cauliflower...), Brassica rapa (turnip, Chinese cabbage...), Brassica napus (rapeseed...) and many more.
Synthetic
Manufactured by chemical and industrial processes. May include products not found in nature, or simulation of products from natural sources (but not extracted from natural raw materials).
Label
is any written, printed or graphic presentation that is present on a product, accompanies the product, or is displayed near the product.
Fungi
Occurring worldwide, most fungi are largely invisible to the naked eye, living for the most part in soil, dead matter, and as symbionts of plants, animals, or other fungi. They perform an essential role in all ecosystems in decomposing organic matter and are indispensable in nutrient cycling and exchange. Some fungi become noticeable when fruiting, either as mushrooms or molds.

Fungi are responsible for a range of serious plant diseases such as blight, grey mould, bunts, powdery mildew, and downy mildew. Crops of all kinds often suffer heavy losses.

Fungal plant diseases are usually managed with applications of chemical fungicides or heavy metals. In some cases, conventional breeding has provided fungus resistantcultivars.

Besides combatting yield losses, preventing fungal infection keeps crops free of toxic compounds produced by some pathogenic fungi. These compounds, often referred to as mycotoxins, can affect affect the immune system and disrupt hormone balances. Some mycotoxins are carcinogenic.
Ectoparasite
A parasite that lives on the outside of its host. Ectoparasites include fleas, ticks, and lice.
IPM
A combination of chemical and biological control methods, based on the concept of economic tresholds. Pest management in organic farming uses many biological control methods developed as par of IPM.
Green manure
A crop grown before or between the main crop rows, cut before maturation and subsequently ploughed in or used as mulch. It provides nutrients to the main crop through decomposition and helps to build up humus in the soil.
organic
Refers to the farming system and products described in the IFOAM standard and not to 'organic chemistry'.
Cruciferae
Cruciferae or Brassicaceae, also known as the crucifers, the mustard family or cabbage family is a family of flowering plants. The name Brassicaceae is derived from the included genus Brassica. The family contains well-known species such as Brassica oleracea (cabbage, cauliflower...), Brassica rapa (turnip, Chinese cabbage...), Brassica napus (rapeseed...) and many more.
Trap crops
Crops planted to attract a pest/pests and then destroyed together with the pest/pests.
Resistance
Ability of a living organism not to get affected by a disease or pest; or of a pest not to be affected by a pesticide.

Pesticide Resistance is the ability of a life form to develop a tolerance to a pesticide. Pests (weeds, insects, mites, diseases, etc.) that become resistant to a pesticide will not be affected by the pesticide. When pests are resistant, it is more difficult to control the pest. Therefore, it is important to try to prevent pesticide resistance.
Cultivar
Cultivar is a plant variety. It is a group of similar plants which through their structural features and performance can be identified from other varieties within the same species.
Chlorosis
Chlorosis is yellowing of leaves.
Endoparasite
A parasite that lives inside its host. Parasite that lives in the internal organs of animals (especially intestinal worms) .
Symptom
Symptom - the plant's response to the disease causing organism, examples are; changes in plant color, death of infected tissues, and wilting. It is the external or internal physical characteristic of a disease as expressed by the host plant.