Microscopic plant-parasitic roundworms that invade roots and stimulate gall or knot formation. In hydroponic and soilless systems they are most likely.
Identification
Root galls: The most characteristic sign is abnormal swelling or knotting on fine and larger roots caused by nematode feeding sites.
Root system: Infested roots may be shortened, branched, rotted, or unable to develop normal fine feeder roots.
Above-ground symptoms: Plants may wilt during warm periods, grow slowly, yellow, or show nutrient deficiency symptoms despite adequate solution fertility.
Distribution pattern: Symptoms often appear in patches or in plants sharing contaminated media, trays, or transplants.
Microscopic pest: The nematodes themselves are microscopic; diagnosis usually relies on root galls, lab testing, or close inspection of roots.
Secondary disease: Damaged roots are more vulnerable to opportunistic pathogens such as Pythium and other root rot organisms.
Lookalikes
Root rot pathogens: Root rot causes browning, slime, and decay, but does not typically create firm rounded galls or knots.
Nutrient deficiency: Nutrient problems can cause yellowing and stunting, but roots will not show characteristic knot-like galls.
Fungus gnats: Fungus gnat larvae damage fine roots in wet media but are visible as black-headed larvae and do not cause true root galls.
Root aphids: Root aphids are sap-sucking insects that may create waxy residues and colonies on roots rather than internal galling.
Environmental Triggers
Warm root-zone temperature: Warm root-zone temperatures speed nematode development and reproduction for many Meloidogyne species.
Cool root-zone temperature: Cooler root zones slow nematode activity and population growth, although some species can survive.
Contaminated media or transplants: Infested media, reused substrate, infected nursery starts, and contaminated tools are major introduction pathways.
Long crop cycle: Long-cycle crops allow multiple nematode generations and greater population buildup.
High sanitation: Clean media, sanitized containers, and pest-free starts reduce introduction and spread.
Resistant cultivars: Resistant cultivars or rootstocks can reduce galling and nematode reproduction for some crop-nematode combinations.
Shared recirculating water: Although root-knot nematodes primarily move with roots and media, shared water and debris can potentially aid movement between plants in contaminated systems.
Treatment
Use clean media and pest-free starts: Use new or properly sanitized soilless media for susceptible crops. Inspect incoming transplants for abnormal root galls before planting. Reject plants with swollen, knotted, or distorted roots. Keep propagation areas separate from potentially contaminated production zones.
Remove infested plants and media: Remove plants showing severe root galling, stunting, or unexplained wilting. Bag roots and attached media before moving them through the grow area. Discard contaminated media rather than reusing it for susceptible crops. Clean spilled media and root debris immediately.
Sanitize containers and tools: Wash soil or substrate particles from trays, buckets, tools, and benches. Sanitize containers and tools between crop cycles using an appropriate disinfectant. Avoid sharing tools between contaminated and clean areas without cleaning. Control movement of used substrate through clean production zones.
Resistant cultivars or rootstocks: Choose tomato, pepper, or other crop cultivars with root-knot nematode resistance when available. Match resistance claims to the likely Meloidogyne species and local conditions. Use resistant rootstocks for long-cycle fruiting crops where appropriate. Do not rely on resistance alone; combine with sanitation and clean media.
Crop rotation with non-host or poor-host crops: Avoid repeating susceptible crops such as tomato, pepper, beans, carrot, and sweet potato in the same contaminated media. Use non-host or poor-host crops where known and compatible with the system. Do not rotate into another susceptible host immediately after an infestation. Discard heavily contaminated media when practical rather than relying on rotation alone.
Heat treatment or solarization of empty media: Apply only to empty media, containers, or beds, never to planted crops. Use verified temperature and time targets appropriate for the media volume. Turn or expose media so heat penetrates evenly. Recontamination can occur if sanitized media contacts dirty tools, roots, or floors.
Biological nematode suppressants: Use only products labeled for plant-parasitic nematodes and edible crops in the target environment. Apply preventively or early before severe galling develops. Follow label instructions for root-zone application, moisture, and compatibility. Combine with clean media, resistant cultivars, and sanitation.
Labeled nematicide program: Use only products explicitly labeled for the crop, root-knot nematodes, and the production environment. Confirm compatibility with hydroponic or soilless systems before use. Follow all restricted-entry intervals, preharvest intervals, worker safety rules, and disposal requirements. Do not use unapproved soil fumigants or systemic nematicides in recirculating hydroponic systems.
Marigold or biofumigant companion strategy: Do not rely on companion planting as primary control for established root-knot nematodes. Use only as a supplementary strategy in media beds where compatible. Avoid adding companion crops that become hosts or crowd the production crop. Prioritize clean media, sanitation, resistant cultivars, and removal of infested plants.
Lifecycle
Eggs in root zone: Females lay eggs in gelatinous masses on or near roots, or eggs are introduced in contaminated media or infected plant material.
Juvenile hatch: Second-stage juveniles hatch and move through water films in the root zone to find suitable host roots.
Root invasion: Juveniles enter young roots and establish permanent feeding sites, causing cells to enlarge and form galls.
Development inside roots: Nematodes mature while feeding inside root tissue, reducing the plant's ability to take up water and nutrients.
Adult reproduction: Females produce new egg masses, allowing populations to increase quickly under warm favorable conditions.
Population buildup and crop decline: Multiple generations can build in long-cycle crops or reused media, causing severe galling, poor growth, and secondary root disease.