Dealing with Root-Knot Nematodes in a Hydroponic System

What Root-Knot Nematodes Do

Root-knot nematodes are microscopic roundworms (Meloidogyne spp.) whose juvenile stages invade plant roots, inducing swollen galls that impair water and nutrient uptake, stunt growth, and predispose plants to secondary infections.

Latin Name

Meloidogyne spp. (e.g. M. incognita, M. javanica, M. hapla)

Identification

Roots show characteristic rounded galls (knots) of varying sizes.
Above-ground symptoms: wilting under heat or drought, yellowing, reduced vigor.
Microscopic examination of root washings reveals vermiform nematodes.

Alternative Names

Gall nematode
Root-knot worm

Varieties (Species)

Meloidogyne incognita (Southern root-knot nematode)
Meloidogyne javanica (Javanese root-knot nematode)
Meloidogyne hapla (Northern root-knot nematode)
Meloidogyne arenaria (Peanut root-knot nematode)

Climates Where They Thrive

Warm media temperatures (20-30 °C) promote rapid life cycles.
Populations decline below ~15 °C or above ~35 °C.
Moist, oxygenated environments favor juvenile mobility in hydroponic reservoirs.

Companion Planting as Deterrents

Cultivar	Hydroponic Methods	Effectiveness
Marigold (Tagetes spp.)	All (DWC, NFT, Ebb & Flow, Drip)	High - roots exude nematicidal thiophenes
Garlic (Allium sativum)	Drip, Ebb & Flow	Moderate - sulfur volatiles disrupt nematode signaling
Cilantro (Coriandrum sativum)	All	Low - attract generalist predators
Mustard (Sinapis alba)	All	Moderate - glucosinolates have soil-sterilant effect

Natural Predators and Antagonists

Steinernema feltiae (entomopathogenic nematode that parasitizes juveniles)
Paecilomyces lilacinus (nematophagous fungus attacking eggs)
Bacillus subtilis strains that induce root systemic resistance

Remedies

Treatment	Hold Period	Natural?	Effectiveness
Hydrogen peroxide flush (3%)	0 days	No	Moderate - oxidative kill of juveniles in reservoir
Beneficial nematode inoculation	0 days	Yes	High - sustained juvenile suppression
Paecilomyces lilacinus drench	0 days	Yes	Moderate - reduces egg hatch rates
Potassium phosphite spray	0 days	No	Moderate - induces plant systemic defense
Copper-based biocide	7 days	No	Low - non-specific; can harm roots if overused

Other Remedies

Trap-crop flush: Cycle susceptible seedlings in reservoir then remove to draw nematodes out of main crop.
Reflective surfaces: Place aluminum foil under trays to deter juvenile settlement.
UV-LED exposure: Brief low-intensity UV in reservoir to inhibit nematode survival.
Silica supplementation: Add potassium silicate to nutrient solution to strengthen root cell walls.

Tips and Tricks

Inspect roots for early gall formation weekly.
Sanitize reservoirs and tubing with 10% bleach between crops.
Rotate host crops or allow fallow periods in reservoir to starve nematodes.
Maintain dissolved oxygen >6 mg/L to discourage juvenile survival.
Combine biological and chemical controls for integrated management.

Common Hosts

Tomatoes, Peppers, Cucumbers
Carrots, Parsnips, Celery
Leafy greens (Lettuce, Spinach)
Herbs (Basil, Mint)