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Root Knot Nematode

S. Sardanelli
Reviewed April 2010

three second-stage juveniles second-stage root-knot nematode juvenile
Light micrograph of three second-stage juveniles of root-knot nematode, Meloidogyne sp. (Eisenback) Scanning electron micrograph of a second-stage root-knot nematode juvenile propped up against a human hair (Eisenback)

What are root-knot nematodes?

  • A worm-shaped, plant-parasitic animal.
  • Nearly microscopic and invisible to the naked eye.
  • One of the most economically damaging plant-parasitic nematodes because of it's wide host range and widespread distribution.

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Root-knot Feeding and Biology

Second-stage juveniles female and egg mass Brown colored egg masses
Second-stage juveniles of root-knot nematode, Meloidogyne sp., penetrating the root-tip of tomato (Eisenback) Root-knot nematode female and egg mass of the root-knot nematode, Meloidogyne sp. (Eisenback) Brown colored egg masses produced by females of the root-knot nematode, Meloidogyne on African violet (Viola sp.). (Zunke)
  • Root-knot juveniles enter the root tips and establish a feeding site, where they remain for their entire lives.
  • The female root-knot nematode lays her eggs on the outside of the roots.

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Root-Knot Nematode Hosts
All major field crops, vegetable crops, turf, ornamentals, and legumes are susceptible to one or more of the root knot species.

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Symptoms of root-knot injury

  • Above ground symptoms are stunting, yellowing, wilting, reduced yield, and premature death of plants.
  • Below ground symptoms are swollen or knotted roots (root galls) or a stubby root system.
  • Root galls vary in size and shape depending on the type of plant, nematode population levels, and species of root-knot nematode present in the soil.
infection on boxwood Galls caused by root-knot Galled root system
Root-knot nematode, Meloidogyne sp., infection on boxwood showing above ground symptoms (Lopez) Galls caused by root-knot, Meloidogyne spp., on boxwood (Overstre) Galled root system of tomato infected with root-knot nematode, Meloidogyne sp., compared with non-infected root system (Eisenback)

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The following widely recognized Integrated Pest management (IPM) strategies are critical to management of root-knot nematodes.

Prevention: This strategy should be the first line of defense. Prevention is the practice of keeping a population of nematodes from infesting a site and specific tactics include:

person taking soil sample
Soil sampling for research and advisory service (Zunke)
  • Education regarding nematode presence, biology, and management.
  • Survey sampling of an intended planting site to determine the degree of existing nematode activity. See "Sampling Procedures" page
  • Use of nematode free transplants.
  • Careful examination of transplant roots before planting can prevent the introduction of nematodes that would attack present and future susceptible plantings.
  • Controlling weeds, which can act as hosts to some species of root-knot nematode.
  • Keep other pests under control.
  • Sanitation practices such as cleaning of equipment between sites of operation.

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Avoidance: practiced when nematode populations exist in a site, but their impact can be avoided or lessened through some cultural practice. Examples of avoidance tactics include:

  • Sampling to determine nematode species and population levels. See "Sampling Procedures" page
  • Choosing plant materials that are poor hosts.
  • Practice crop rotations that include nonhost, resistant and susceptible crops when feasible.
  • Employ cultural practices known to be optimal for plant growth.
  • Root barriers and container growing.
  • Isolate/destroy plants that are known to be infested with root-knot nematodes and replace infested soil.

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Monitoring: includes tracking and proper identification of nematodes and includes:

  • Soil and plant sampling for detection and trouble shooting.
  • Routine sampling to maintain records of incidence and distribution. These samples form the basis for crop rotations, cultivar selection, economic thresholds, suppressive actions, and other management decisions.

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Suppression: nematode suppressive tactics may become necessary to avoid economic crop loss where prevention and avoidance tactics are not successful.

Suppressive tactics include:

  • Cover crops and Green manures improve the fertility of the soil. As the plant material decays, the nutrients are released into the soil and are taken up by the subsequent crops planted in the soil. However, the time that is required for the cover crops or green manures to fully decay and penetrate to the root zone varies and can take up to an entire year. Both cover crops and green manures increase the bacteria, fungi, and other microorganism populations in the soil, which can aid in reducing root-knot numbers. When a cover crop is tilled into the soil (turned in) it is then referred to as a green manure.
  • Soil amendments, such as compost and manure, and mulches with high organic matter will increase the chances that root-knot antagonistic organisms will develop.
  • resistant to susceptible comparison

    Rice root system resistant(top) to root-knot compared to susceptible (bottom) (Diamonde)

    Crop rotation is the planting of different crops in different portions of the field/ garden each year. It is used to gradually reduce high populations over a number of years or to prevent a low population from becoming high.
  • Fallow period with no susceptible plants for a period of one to two years (in the area with high root-knot populations) can significantly reduce the population size.
  • Resistant varieties can prevent root-knot nematode reproduction (reducing populations significantly), have no requirements for special application techniques or equipment (as in the case of chemical management), and have similar costs to non-resistant cultivars. They can be used in addition to other suppressive mechanisms such as crop rotation and soil amendments.
  • Soil solarization uses the natural heat from the sun to reduce nematode populations. Prior to planting, when the soil can receive the most direct sunlight, it is covered with a plastic polyethylene tarp for four preferably six weeks.

  For additional information visit the  Nematode Suppressive Crops page at- Auburn University -

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Chemical Management: Chemical control involves the application of certain volatile (fumigants) and nonvolatile nematicides to the soil to reduce nematode populations. Chemical management reduces nematode populations for a limited period of time. Nematodes that escape treatment can resume feeding when the chemical is gone. Recommendations for the application of nematicides may be found in the University of Maryland's current Extension publications.


All pictures are courtesy of Nemapix Jounal of Nematological Images, vol. 1 &2, J.D. Eisenback & Ulrich Zunke, eds.

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