Root-knot nematodes (Meloidogyne spp.)
Symptoms of infestation by root-knot nematodes are similar in all crops: wilting of plants and if infested plants are pulled from the soil the roots can be seen to be distorted, swollen and bearing knots. The infested roots eventually rot and affected plants die.
- Use resistant varieties, if available.
- Practise mixed cropping. Mixed cropping with African marigold (Tagetes spp.) minimises root-knot nematode damage. Intercrop with different mustards (e.g. Brassica juncea var. integrifolia or Brassica juncea var. juncea) on infested fields. As soon as mustards are flowering they are mulched and incorporated into the soil. While incorporated plant parts are decomposing in a moist soil, nematicidal compounds of this decomposing process kill nematodes. Two weeks after incorporating plant material into the soil a new crop can be planted or sown (phytotoxic effects are usual if the crop is planted before two weeks).
- Maintain high levels of organic matter in the soil (manure or compost).
- Use biofumigation where possible (biofumigation involves incorporation into the soil of crop residues of crucifers, resulting in high levels of organic matter).
- Use Neem extracts.