Root-knot nematodes
Microscopic soil worms that invade roots and cause knobbly swellings, leaving plants stunted and prone to wilting.
Also known as: Eelworms, Root galls
Symptoms and identification
Plants grow slowly, look pale and wilt in the heat of the day even when the soil is moist. When lifted, the roots show round or knotted swellings (galls) that cannot be rubbed off, unlike the nodules on beans and peas.
Causes
Nematodes live in warm, sandy soils and build up when the same crops are grown in the same place year after year. They spread in infested soil, on tools and in the roots of transplants.
Organic treatment
Pull and bin affected plants with their roots. Mix neem cake into the soil at about 250 g per square metre before replanting. In summer, soil solarisation (covering moist soil with clear plastic for 4–6 weeks) greatly reduces numbers.
Prevention
Rotate crops, use fresh potting mix in containers, and add plenty of compost to encourage soil life that keeps nematodes in check. Grow marigolds as a cover crop or between rows; their roots suppress nematodes.
Chemical treatment (use with care)
Chemical nematicides are not recommended for home gardens. Rely on rotation, solarisation, neem cake and resistant varieties.