Root-knot nematodes (Meloidogyne spp.) can multiply rapidly on a large number of host plants. These nematodes can cause great economic damage because infected propagation material, such as seed, potatoes and flower bulbs, can be rejected. In addition, root-knot nematodes can cause quality and yield reductions. Root-knot nematodes are a particular problem on sandy, valley, sandy lutite and light clay soils.
Root-knot nematodes affect the physiology of the plant. Giant cells are formed at the sites where the nematodes penetrate the root. This can be seen on the outside by a nodule or a thickening of the root. The eggs are laid in and on the nodules in a somewhat gelatinous package. One packet contains 300 to 500 eggs. The eggs hatch spontaneously when the soil temperature rises above 5-10°C.
Attractants play no role in root-knot nematodes. Therefore, natural mortality is very high in the absence of a suitable host plant or black fallow. Most species of root-knot nematode (except M. naasi) have 2-3 generations per growing season. The combination of multiple generations and the high number of eggs laid allows a population to increase dramatically within a year.