Root-Knot Nematode

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Nematoda: Heteroderidae (Meloidogyne spp.)


Root-knot nematodes are microscopic roundworms that cannot be detected by the naked eye. They are usually between 0.5 to 1.5 millimeters in length and 0.03 to 0.7 millimeters in diameter. Root-knot nematodes live in the soil and attack the root of a wide variety of plants. They can become serious pests in the home garden by feeding on root cells with their needle-like mouthparts.

Life Cycle

The length of a root-knot nematode life cycle varies among species but on average it completes in 25 days. Up to 1000 eggs of the nematodes can be laid inside the root tissue or into the soil. When the eggs hatch, the second-stage juvenile emerges which is the infective agent penetrating roots. They migrate to and infect adjacent parts of the root or tubers. They spend the third and fourth juvenile stages in the plant. After the fourth juvenile stage, adults emerge, mate, and reproduce. Root-knot nematodes are spread by water, soil clinging, farm equipment, or on infected propagating stock transported into uninfected areas. Root-knot nematodes complete three to five generations per year.


Root-knot nematodes attack the roots and tubers of various plants including tomatoes, potatoes, and carrots. This pest causes irregular galls on roots and tubers that interfere with the movement of water and nutrients within the plant. Infected plants such as tomatoes are stunted, appear yellow or pale green, and produce fewer and smaller fruits. The symptoms in root crops such as carrots may be deformed (forked carrots) or hairy roots with nodules. In potatoes, root-knot nematodes reduce the vigor of plants and cause blemishes on tubers.