Root-knot Nematode
Meloidogyne spp.
Microscopic soil-dwelling worms that form knotty galls on roots, stunting and sometimes killing vegetable plants.
Background
Root-knot nematodes are the most damaging plant-parasitic nematodes in Australian home gardens. Several Meloidogyne species are present, with M. incognita, M. javanica and M. hapla the most common. The worms infect root tips, causing cells to swell into characteristic galls. Affected plants wilt in hot weather even when soil is moist, yellow prematurely and yield poorly. Light sandy soils with continuous cropping of susceptible vegetables are the worst case.
How to identify
- Adults and juveniles: microscopic (<1mm), cannot be seen without a microscope
- Damage: knotty swollen galls along roots (distinct from legume nitrogen nodules — galls cannot be rubbed off)
- Above ground: wilting during hot days, yellowing, stunting, uneven growth along a row
Life cycle
Juveniles hatch from eggs in soil, invade root tips, establish a feeding site that becomes a gall. Females swell and lay hundreds of eggs inside the gall. Life cycle 3-8 weeks depending on temperature.
Weather triggers
- Temperature: 15-32°C
- Most active in warm soils above 18C. Populations drop over cold winters but survive in roots.
Peak season (southern hemisphere)
Red = active season · Dark red outlined = this month
Affected vegetables & crops
Click any crop to see current prices and growing info.
Climate zones at risk
Organic & low-impact control
- Heavy soil organic amendment (compost, manure, biochar) boosts microbial antagonists
- Solarisation — cover moist soil with clear plastic for 6-8 weeks in peak summer
- Rotate with resistant crops (sweet corn, marigold cover crop, leeks)
- Plant resistant tomato varieties (look for VFN in the cultivar code)
Chemical control
- Synthetic nematicides are not available to home gardeners and are highly restricted for professional use
Always read product labels — registrations change.
Prevention
- Rotate vegetable families — do not grow solanaceous or cucurbit crops in the same bed year after year
- Use French marigold (Tagetes patula) as a living cover crop and dig in before planting
- Raise organic matter — nematode-suppressive soils tend to be biologically active
Companion planting
Tagetes patula (French marigold) grown as a cover crop for 8-10 weeks before incorporation has documented suppressive effects. Single marigold plants dotted between vegetables are not enough.
Biosecurity
Widely established in Australian gardens.
Sources
- NSW DPI — Root-knot nematode in vegetables
- Queensland DAF — Nematodes in vegetables
- Agriculture Victoria — Root-knot nematode
Accuracy confidence: high. We update this library as new extension guidance is published.