Microscopic roundworms found in soil. Most are beneficial (feeding on bacteria and fungi, cycling nutrients) but some species parasitise plant roots, causing galls and wilting. Beneficial nematodes can be used to control soil pests.
Nematodes are among the most abundant organisms in Australian soil, with both free-living and parasitic species present across all climate zones. Free-living nematodes play a crucial role in soil health by decomposing organic matter, cycling nutrients, and preying on harmful bacteria and fungi. However, root-knot nematodes and root-lesion nematodes are serious plant parasites that damage vegetables, fruits, and ornamentals, particularly in warm climates like coastal Queensland and northern NSW.
Root-knot nematode damage appears as galled, knotted roots that prevent nutrient and water uptake, causing wilting and stunted growth. These parasites thrive in summer (December-February) when soil temperatures exceed 20°C. To manage nematodes, practise crop rotation with resistant varieties, incorporate organic matter to encourage beneficial nematodes, and maintain proper soil moisture. In warmer zones (8-11), solarisation—covering soil with clear plastic during hot months—can reduce nematode populations.
You can purchase nematode-resistant seedlings from Bunnings and local nurseries. Avoid moving infested soil between garden beds, and clean garden tools between use. Beneficial nematodes (Steinernema and Heterorhabditis species) can be purchased as biological controls to manage soil-dwelling pests like grubs and weevils, though they're most effective in autumn and spring when soil temperatures are 12-25°C.