Nematodes (root-knot & others)
Microscopic root-attacking worms that gall, rot or stunt the roots, so the plant looks starved, wilts in heat and yields poorly despite good feeding.
- Pathogen
- Plant-parasitic nematodes (Meloidogyne etc.)
- Spreads by
- Soil, water, tools & planting material
- Favoured by
- Susceptible crops grown continuously; light soils
- Main risk
- Galled/rotted roots; stunting, wilting, low yield
Overview
Plant-parasitic nematodes are microscopic worms in the soil that feed on plant roots. The most common and damaging are the root-knot nematodes (Meloidogyne), which cause the roots to swell into knots or galls; others (cyst, lesion, burrowing, reniform nematodes) rot, lesion or stunt the roots instead. Because the damage is on the roots, the above-ground symptoms are non-specific — patchy stunting, yellowing, a starved look, mid-day wilting even with enough water, and poor yield despite good fertiliser — so nematodes are often missed and blamed on "poor soil".
The give-away is in the roots: pulling up an affected plant shows the characteristic knots/galls of root-knot nematode, or rotted, stubby, poorly-branched roots. Damaged roots also open the door to wilt and rot fungi, worsening those diseases. Nematodes build up in the soil under susceptible crops and are spread in soil, water, and on tools and planting material. Because they are hidden and hard to kill once the crop is growing, management is mostly preventive and pre-plant: resistant varieties, rotation, summer soil solarisation/deep ploughing, organic amendments and bio-agents.
How to identify it
- Patchy stunting, yellowing and a starved look, with mid-day wilting even when soil moisture is adequate.
- Poor yield and vigour despite good fertiliser — the plant cannot use it with damaged roots.
- On pulling up the plant: characteristic knots/galls on the roots (root-knot), or rotted, stubby, poorly-branched roots.
- Damage in patches that expand year to year under susceptible crops, and more wilt/rot on nematode-damaged roots.
What causes it and when
- Microscopic plant-parasitic nematodes — most often root-knot (Meloidogyne), plus cyst, lesion, burrowing and reniform types — feeding on the roots.
- Build up in the soil under susceptible crops grown continuously, especially in lighter, sandy soils.
- Spread in soil, irrigation water, and on tools, machinery and infected planting material/seedlings.
- Damaged roots also let in wilt and rot fungi, so nematodes often worsen those diseases.
Cultural & organic control
- Grow nematode-resistant varieties/rootstocks where available, and raise clean, nematode-free nursery seedlings.
- Rotate with non-host or antagonistic crops (e.g. cereals, marigold) to run down soil populations.
- Solarise the nursery/field soil in summer and deep-plough to expose and reduce nematodes.
- Add organic matter, neem cake and bio-agents (e.g. Trichoderma, Purpureocillium/Pochonia) that suppress nematodes.
Chemical control
- Because nematodes are hard to reach once the crop is growing, control is mostly pre-plant and cultural.
- Where recommended, a CIB&RC-registered nematicide/bio-nematicide can be applied at planting in high-value crops.
- Combine any nematicide with resistant varieties, rotation, solarisation and organic amendments — chemicals alone rarely suffice.
- Confirm the current nematode-management package for your crop with your local KVK.
Prevent it coming back
- Base the crop on resistant varieties/rootstocks, clean seedlings and rotation with non-hosts/marigold.
- Solarise and deep-plough in summer, and build up organic matter, neem cake and bio-agents.
- Avoid carrying infested soil, water or seedlings into clean fields, and clean tools between fields.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My plants are stunted and wilt in the heat despite enough water and fertiliser. Could it be nematodes?
Quite possibly. Patchy stunting, a starved look, mid-day wilting with adequate moisture, and poor yield despite good feeding are classic signs of root damage — and if you pull up a plant and see knots or galls on the roots (root-knot nematode), or rotted stubby roots, nematodes are the cause. They are managed mainly before planting: resistant varieties, rotation (marigold helps), summer soil solarisation, organic matter and bio-agents.
What are the knots or galls on my plant’s roots?
Those swollen knots or galls are caused by root-knot nematodes (Meloidogyne) feeding inside the roots and making them balloon. The galls block the roots’ ability to take up water and nutrients, which is why the plant looks starved and wilts even with enough water. Seeing them confirms a root-knot problem and warns the soil is now infested, so plan resistant varieties, rotation, solarisation and bio-agents before the next crop.
Why are nematodes so hard to control once the crop is growing?
Because they live in the soil around and inside the roots, out of reach of foliar sprays, and by the time you see the above-ground symptoms the roots are already damaged. That is why nematode management is mostly preventive and pre-plant: resistant varieties and rootstocks, rotation with non-hosts and marigold, summer soil solarisation and deep ploughing, and building up organic matter and bio-agents that suppress them — rather than trying to rescue an infested growing crop.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.