Root-Knot Nematodes
Pest · Commonly affects: Tomatoes, Carrots, Okra, Cucumbers, Peppers, Melons
Root-knot nematodes are microscopic roundworms in the genus Meloidogyne that live in the soil and feed inside plant roots. They matter to gardeners because they are among the most widespread and damaging soil pests, quietly stunting vegetables and cutting yields, especially in warm regions and sandy soils.
How to identify it
Because the worms themselves are too small to see, you diagnose them by symptoms. Aboveground, affected plants wilt in midday heat even when the soil is moist, stay stunted and pale, and often grow poorly in scattered patches across a bed. The sure sign is belowground: pull up a struggling plant and look for swollen galls or knots along the roots that are part of the root itself and cannot be rubbed off, which sets them apart from the loose, easily detached nodules found on healthy bean and pea roots.
Damage
The galls disrupt the roots' ability to draw up water and nutrients, so plants remain small, wilt readily, and set little fruit. Heavy infestations can kill young transplants outright and create wounds that let soil-borne fungi and bacteria move in, making root rots and other diseases worse.
Prevention
Rotate away from susceptible vegetables for two or more seasons, using grasses, small grains, or other non-host cover crops that the nematodes cannot feed on to starve down their numbers. Choose vegetable varieties bred for nematode resistance, such as tomatoes marked with an "N" in their disease-resistance codes, and give plants proper spacing so roots stay vigorous. Build healthy soil with regular additions of compost and organic matter to support competing soil life, and practice good sanitation by cleaning soil off tools, boots, and equipment so you do not carry infested dirt from bed to bed.
How to manage it
Since these pests cannot be picked off by hand, rely on cultural and mechanical steps: pull and destroy heavily galled plants at the end of the season instead of tilling the roots back in, and never add infested roots to the compost pile. Growing French marigolds or certain mustards as a cover crop and turning them under as a green manure helps suppress populations, and covering moist bare soil with clear plastic during the hottest weeks of summer can reduce numbers in the upper layer. Keep plants evenly watered and mulched so weakened roots can better tolerate the feeding, and add compost to encourage beneficial soil organisms, including nematode-trapping fungi, that help hold populations down.
General guidance for US home gardens, focused on prevention and non-chemical control. For a confirmed diagnosis and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.