What are Nematodes?

Nematodes, also known as eelworms and roundworms, are of the most abundant creatures living in soil. Nematode species are very difficult to distinguish, over 28,000 have been described, of which 16,000 are parasitic. The total amount of nematode species has been estimated to be about 1 million. Although some of these tiny, worm-like animals are beneficial, about 50% are detrimental to plant life and on a global scale it has been estimated that these parasitic species reduce agricultural production by a figure in the order of 12%.

Plant parasitic nematodes behave in different ways, some feed externally on plant roots whilst others invade the roots internally. The resultant damage that nematodes cause food crops worldwide can vary from a reduction in yield and/or reduced marketability of the affected crop. The damage sustained by an individual crop will of course vary from field to field and will be influenced by a wide range of factors. These factors will include the density of the nematode population, the virulence of the species or strain which has targeted the individual crop and the level of tolerance / resistance which the affected crop can muster against the attack.

One of the big problems with nematode attacks is that the visual damage which results, such as stunted plants and leaf discolouration, is all too often attributed to alternative causes. It is often the case that plants which fail to respond normally to fertilisers or which exhibit a very slow recovery from wilting are actually being affected by plant parasitic nematodes. It is worth remembering that nematode feeding can result in ‘open wounds’ on the host plant which then allows entry for a wide range of fungi or bacteria.

Types of Nematodes

Nematodes are parasites are actively present in almost any soils cultivated by man.

The word nematode comes from the Greek words Nema, which means thread and the word Toid which means form. Nematodes are microscopic worms 0,1 mm in length and they vary in population density depending on the soil type and plants being grown. There are many types of nematodes, some induce the host plant to produce nutrients which the nematodes can survive on, some enlarge the plant root structures which they then live in or some do both.

Symptoms of Nematode Damage

Crop damage caused by nematodes differ depending on the crop, however here are a few of the most common symptoms.

  • Damaged plants in patches along a row
  • Stunted plants
  • Wilted and plants without vigour
  • Yellowing
  • Stem distortion
  • Crown and bulb swelling
  • Root galls
  • Root distortion and unusual growth
  • Plant death