What are Nematodes?

Nematodes are tiny roundworms that are found in almost every ecosystem on earth. More than a million nematodes can be found within just 1 sq m, and they account for about 80% of all individual animals on earth. Nematodes can be relevant to gardeners as they can affect the garden and its plants in both negative and positive ways. Some nematodes can cause problems for your plants, while others can be beneficial. Understanding these fascinating creatures can be helpful in order to develop a successful organic garden.


Detrimental Nematodes


Nematodes can be detrimental in a garden in certain ways. For example, there is one nematode called the potato cyst, which can decimate your potato crop. There are a number of different nematodes which will burrow into plant roots and make their way up the stems and into the leaves. The damage they do can make it difficult for plants to absorb the nutrients they need, which can result in small, weak plants – or even kill plants outright.

Dealing with detrimental nematodes generally involves:

  • Taking care over companion planting (marigolds may be beneficial) & crop rotation.
  • Making sure plants are healthy and well-watered, so they are better able to withstand nematode attack.
  • Incorporating plenty of organic matter into the soil to suppress certain nematodes and keep them from doing as much harm.
  • Taking care with sanitation and plant removal to avoid contaminating further areas.

Negative nematodes can also be combatted by introducing natural antagonists of the nematodes involved to your garden. Examples include the fungus Gliocladium roseum. Some gardeners also use Chitosan, a natural biocontrol, which causes plant defence responses to destroy parasitic cyst nematodes on crop roots without harming beneficial nematodes in the soil. It is made by treating the chitin shells of shrimp and other crustaceans with an alkaline like sodium hydroxide.

Beneficial Nematodes


As mentioned above, however, not all nematodes that are in the soil in your garden are bad for your plants, or for you as the gardener. Nematodes serve important ecological purposes in the soil ecosystem. Nematodes can help to effectively regulate the bacterial population of the soil – some eat up to 5,000 bacteria per minute. Some nematodes also play a vital role in the nitrogen cycle by way of nitrogen mineralisation.

Using Nematodes for Biological Pest Control


Nematodes are also frequently uses as a biological pest control in organic gardens. In such cases, beneficial nematodes are deliberately introduced to the soil ecosystem. Pathogenic nematodes are frequently introduced to deal with pest problems, such as issues with slugs etc..

While this can be used as a solution in the case of extreme pest infestation, it is generally better to consider other organic methods of pest control. If you introduce nematodes, for example, to kill off all the slugs in your garden, you can inadvertently make the problem worse, since, by getting rid of the slugs, you can upset the natural balance in your garden.

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