Severe root-knot nematode symptoms on Swiss chard roots

Severe root-knot nematode symptoms on Swiss chard roots

Updated: April 27, 2021

Appearance

  • Root-knot nematodes are very small (0.5 to 0.75 mm), colorless roundworms.
  • The most common root infecting nematodes of vegetable crops are two root-knot nematode species, Meloidogyne hapla and Meloidogyne incognita.

Life cycle/habits

  • They dwell in the soil, enter plants' roots as tiny larvae, and cause swellings (root knots) that can be easily seen (distinguishable from the nitrogen-fixing nodules found on legumes because the latter can be easily rubbed off the roots whereas root-knots are firmly attached).
  • Both species thrive in a wide variety of soil types but are more commonly found on light-textured soils (those with a high percentage of sand).
  • The root-knot nematode takes about 27 days to grow from egg to adult under normal growing season temperatures.
  • The immature root-knot nematode molts once in the egg, emerges as the infective larval stage, and enters plant roots.
  • The female nematode remains inside the root for the rest of her life, causing the swelling or "root-knot" to be formed around her body, which swells into a spherical shape.
  • At maturity, the female extrudes her eggs into a tan gelatinous mass that can be seen on the root-knot surface.
  • Each female can produce one egg mass containing from 300 to 500 eggs.
  • Some nematodes also serve as vectors for plant virus diseases such as tomato ring spot and tobacco ringspot.
Root-knot nematode swellings (nodules) on bean roots
Root-knot nematode swellings (nodules) on bean roots

Host plants

  • Most vegetable crops may serve as host plants.

Signs/symptoms

  • Swellings or nodules on plant roots can indicate root-knot nematodes.
  • Plants fail to establish, are stunted, wilt in hot weather, and decline.
  • Affected plants produce fewer and smaller fruit.
  • Root crops such as carrots may be deformed (forked carrots) or have hairy roots with nodules.
  • Symptoms spread through a site as the season progresses and succeeding generations of juveniles hatch out.
  • On left stunted and forked carrots.
    Photo: S.A. Johnson, Rutgers

    On left stunted and forked carrots
  • Yellowing of plants in patches in a field infested with root-knot nematode.
    Edward Sikora, Auburn University, Bugwood.org

    yellowing crops in a field with root knot nematodes in soil

Monitoring

  • Soil and tissue testing is the only accurate method to determine that nematodes are the cause of plant injury. Microscopic examination is required to identify these tiny worms.

Prevention/Control

  • Prevention and biological control are the keys to success in managing this pest.
  • There are no chemical treatments available to home gardeners.
  • Plant only resistant varieties of susceptible plants. Resistant tomato cultivars will have an "N" after the cultivar name (usually VFN for tomato).
  • Keep weeds down and rotate susceptible crops or avoid planting them for a few years.
  • Pull up and remove badly infested plants.
  • Some "green manure" crops (cover crops), such as mustard and rape, produce compounds that suppress root-knot nematodes.
  • Enhancing the biological activity of the soil, through the incorporation of compost, can also help suppress root-knot nematode populations.
  • Dig up suspect plants, wash soil off the roots, and carefully inspect for swellings. If root-knot is strongly suspected have your soil tested and follow recommendations.