Root-Knot Nematode
Meloidogyne incognita, M. javanica, M. hapla, M. arenaria
Overview
Root-knot nematodes (Meloidogyne species) are sedentary endoparasites that induce distinctive galls on roots of vegetables, fruits, and ornamentals. Second-stage juveniles invade root tips, and females establish feeding sites that cause knots and disrupt water uptake. Warm sandy soils favor high populations. Damage is especially severe on tomato, pepper, cucumber, carrot, and many flowers. Infested beds show declining yields over successive seasons unless rotations, resistant cultivars, and soil biology practices interrupt the nematode life cycle.
Symptoms
Roots develop rounded galls or knots of varying size; severe infections produce swollen, distorted root systems with few healthy laterals. Above ground, plants wilt in midday heat, remain stunted, and yellow despite watering. Fruit set and root-crop quality decline. Carrots may fork or become galled. Galls differ from nitrogen-fixing nodules: root-knot galls are swellings of the root itself and are not easily rubbed off. Secondary wilts often invade damaged roots.
Environmental Conditions
Hot
Prevention
Inspect transplant roots for galls before planting and reject infested stock. Do not share garden soil or tools from known hot spots without cleaning. Build organic matter and avoid bare, overworked sandy soil. Map patchy decline so you can isolate problem areas. Choose resistant cultivars as a routine for solanaceous and cucurbit crops in warm climates. Keep records of rotations to prevent accidental return of highly susceptible crops too soon.
Management
Plant resistant tomato and pepper cultivars with Mi or other resistance genes where the local Meloidogyne species is controlled by those genes. Rotate with non-host or poor-host crops and use antagonistic cover crops such as certain marigolds in carefully managed sequences. Add compost and maintain active soil biology. Solarize beds in hot summers where climate allows. Remove and destroy heavily galled roots rather than tilling them back in. Avoid moving soil from hot spots to clean beds.