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How to identify it
- Above ground, plants look stunted and discolored, wilt easily in hot, dry weather and may seem short of nutrients, so the symptoms alone aren't proof.[1]
- Dig up a plant and check the roots: large and small roots carry round swellings (knots or galls), and the root system may be shallow, with dead areas or too much branching.[1][2]
- True galls are swellings of the root itself and can't be rubbed off, unlike the nitrogen-fixing nodules on bean and pea roots, which are normal.[2]
- The nematodes are too small to see without a microscope; a lab test confirms them, or a simple bioassay: melons sown in pots of moist garden soil kept near 80 °F develop visible root galls in about 3 weeks if root-knot nematodes are present.[2][1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Nitrogen-fixing nodules on legumes | Normal nodules on bean and pea roots sit on the surface and rub off; root-knot galls are swellings inside the root.[2] |
Where it lives
Widespread, especially in sandy soils such as South Carolina's Coastal Plain and river deltas, and the most damaging garden nematodes in California; a newer species, Meloidogyne enterolobii, has been introduced into Florida, North Carolina and South Carolina.[1][2][3]
Biology and life cycle
Plant-feeding nematodes pass through an egg stage, four immature stages and an adult stage, and can go from egg to egg-laying adult in 21 to 28 days in warm summer weather; root-knot females swell into a pearlike shape inside the gall.[2]
They survive between seasons mainly as eggs in the soil; the second-stage juveniles invade roots, usually at the tips, and the plant forms a gall where they feed.[2]
They spread easily from garden to garden in soil on tools, tillers and boots and on infested plants.[2]
Damage and signs
- Galls damage the roots' ability to carry water and nutrients and can crack open, letting in soil-borne disease organisms; heavily infested plants may die.[2][1]
- Hosts include tomatoes, okra, beans, sweet potatoes, cucumbers, melons, squash, peppers, carrots and lettuce, plus many fruit trees and ornamentals; begonias, coleus and impatiens are among the bedding plants most likely to be damaged.[2][1][3]
Health risk
They attack plant roots only; none of the sources reports any risk to people or pets.[1][2]
Control
Prevention
Plant resistant varieties: tomatoes marked 'N' resist most root-knot species, Clemson lists resistant southernpeas, lima beans, peppers, sweet potatoes and tomatoes, and zinnia, salvia and marigold are resistant bedding plants.[2][1]
Rotate: about three years of non-host crops such as asparagus, corn, onions, garlic and strawberries in a bed reduces the population.[1]
Sanitation
Clean soil off tools, tillers and boots before moving between gardens, and start with clean, inspected transplants.[2][1]
Traps and physical control
Solarize moist, tilled soil under clear plastic for 6 to 12 weeks in summer, or till every 10 days through a hot, dry summer so the sun dries out the nematodes.[1]
Common questions
- Why are there knots on my tomato roots?
- Round swellings that are part of the root, on both large and small roots, are the classic sign of root-knot nematodes.[1][2]
- My resistant tomatoes still have galls. Why?
- Resistance doesn't cover every root-knot species; in Florida and the Carolinas, galls on resistant varieties may point to Meloidogyne enterolobii, a newer introduced species.[3][2]
Sources
- Clemson Cooperative Extension, Home & Garden Information Center, “Root-Knot Nematodes in the Vegetable Garden (HGIC factsheet).” hgic.clemson.edu/factsheet/root-knot-nematodes-in-the-vegetable-garden/ (accessed 2026-10-17)
- University of California Statewide IPM Program, “Nematodes (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/nematodes/ (accessed 2026-10-17)
- Clemson Cooperative Extension, Home & Garden Information Center, “Meloidogyne enterolobii (M.e.) and the Challenge for Home Gardeners.” hgic.clemson.edu/meloidogyne-enterolobii-m-e-and-the-challenge-for-home-gardeners/ (accessed 2026-10-17)
- iNaturalist, “Meloidogyne taxon page (order and family).” www.inaturalist.org/taxa/460866 (accessed 2026-10-06)