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Root-knot nematodes

Also known as Meloidogyne, Root-knot eelworms

PestHarmful
Meloidogyne incognita galls and nodules Photo: David B. Langston, University of Georgia, Bugwood.org · CC BY 3.0 us

In short

Root-knot nematodes are microscopic roundworms that live inside roots and make them swell into knobbly galls. Galled roots take up water and nutrients poorly, so plants wilt, yellow and grow slowly. They are most serious in warm climates and sandy soils.

How it looks

Too small to see without a microscope. The visible sign is the root: swollen, lumpy galls up to about 2.5 cm (1 inch) across, which are part of the root itself. Inside a gall, adult females are swollen and pear-shaped and lay hundreds of eggs in a jelly-like mass. The galls should not be confused with the nitrogen-fixing nodules on the roots of beans, peas and other legumes, which rub off easily; nematode galls do not.

Signs

Wilting in the heat of the day even when the soil is moist, yellowing, stunting, poor flowering and fruiting; when the plant is lifted, roots are swollen and knotted.

Life cycle

Egg, four juvenile stages and adult. Second-stage juveniles hatch in the soil, enter a root and settle to feed, triggering the gall; females stay embedded in the root. The cycle can be as short as three to four weeks in warm weather; they cannot invade roots when the soil is below about 18 °C (64 °F).

What favours it

Warm, moist, sandy soils; tropical and subtropical climates and short winters. Spread in infested soil, on tools and with infected plants.

Prevention

  • Use clean, bagged potting mix for containers rather than garden soil.
  • Buy healthy plants and check roots for galls before planting.
  • Clean tools and pots after working with infested plants.
  • Choose resistant vegetable varieties (for tomatoes, look for "N" in the variety code, e.g. VFN).

Treatment

Start with the first step and move down only if the problem persists.

  1. In pots, discard the infested plant and its mix and clean the pot before reuse.
  2. In beds, rotate to resistant or non-host plants, or leave the ground fallow for a season.
  3. Solarise bare, moist soil under clear plastic for four to six weeks in the hottest weather.
  4. Keep affected plants well watered and fed to reduce stress while they finish the season.

Pros and cons

Cons

  • Invisible until roots are examined; spreads easily in soil.

Look-alikes

Nitrogen-fixing root nodules
Found on beans, peas and other legumes; a normal, beneficial partnership with bacteria. Nodules rub off the root easily, galls do not.
Crown gall
A bacterial disease that forms larger, rough galls mostly at the crown or on stems.
Root rot
Roots dark and mushy rather than swollen and knotted.

Affected plants

About 2,000 plant species, including tomatoes, peppers, cucurbits, carrots and many ornamentals and woody plants.

Sources

  1. Nematodes — UC IPM Pest Notes
  2. Root-knot nematode — Wikipedia

Written in our own words from these sources. Check a product label before using any treatment.