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By Luke Sholl Reviewed by: Gloria Payá

Nematodes are microscopic or macroscopic worm-like creatures that can live almost anywhere. Also known as roundworms, they can be either parasitic or free-living. This means that out of the approximately 25,000 known species of nematodes, roughly 50% are predatory, while the other half works in favour of its environment.


Nematodes can adapt and live under numerous conditions, be it in sub-zero polar temperatures, high-salt and pressure zones like the deep sea, fresh water sources, or even the desert.

In agriculture, nematodes can be either detrimental or beneficial to plants. In fact, some species are so aggressive they are considered parasitic and can cause devastation of entire plantations.

One such example is the root-knot nematode, which as the name implies, works by entangling itself around the roots and swelling up, forming huge abnormal galls. There are five types of nematodes that attack the roots, and one that attacks the stems—the stem nematode. This one will cause swelling and atrophy of the stems and leaves, severe stunting, and even wilting. The result is more often than not an irrecoverable crop. Luckily, this doomsday scenario is relatively easy to prevent.

On the other side of the spectrum, we have the good guys. Free-living nematodes will actively seek and destroy major pests to the cannabis plant, over 200 of them. From fungus gnats, fleas, termites, Japanese beetles and many more, they prey on the larval state of these pests by infecting them with plant-safe bacteria that destroys the host from the inside out. Very often, they will also insert their own larvae to feed off and grow from within the host.


The best line of defence against bad nematodes is prevention. While there are numerous pesticides you can use, they will also equally eradicate a significant amount of the good microbiology around the rhizosphere—the living ecology surrounding the roots.

Moreover, the use of pesticides that are considered safe to ingest may become very toxic when smoked. For example, myclobutanil, which is safe for human consumption, turns into hydrogen cyanide when combusted, which is a dangerous poison.

The best tactic is to keep everything healthy. An overused or improperly recycled soil is a playground for parasitic nematodes. Stagnant water is always a bad idea. Keeping the topsoil layer dry will prevent 90% of nematode species and other pests from laying eggs. Numerous beneficial bacteria—like Pasteuria penetrans—also have the ability to destroy eggs and larvae. Even some mushroom species are capable of destroying fully developed nematodes, like Arthrobotrys oligospora or Entomophthora gypsophila.

So, by keeping your substrate fresh, cultivating beneficial bacteria, being sure wet-dry cycles are balanced, and oxygenating your water, you can work wonders against parasitic nematodes while promoting beneficial nematodes.

You can also inoculate your cannabis plants with selected nematodes for added defence and healthier plants. Nematodes can be cultured, similar to beneficial bacteria, but they have a very short shelf-life. They are readily available from any agriculture pest-control company. Best of all, these products are often OMRI certified, which is excellent for pure organic growers.

Symbiotic Nematodes

Heterorhabditis bacteriophora will help prevent
  • Ticks
  • Ant queens
  • Adult fleas
  • Humpback flies
  • Leafminers
  • Gall midges
  • Numerous moths
  • Several weevils
Steinernema carpocapsae will help prevent
  • Black cutworms
  • Caterpillars
  • Flea larvae
  • Fly larvae
  • Webworms
  • Wireworms
  • Wood borers
  • Several weevils
Steinernema Feltiae will help prevent
  • Black cutworm
  • Fungus gnats
  • Pill worm
  • Root maggots
  • Shore flies
  • Subterranean termites
  • Ticks
  • Several weevils


Inoculating your substrate with nematodes is as simple as mixing them with plain unchlorinated water and spraying it on the topsoil. It is advised not to mix the species together; instead, spray them one at a time on different days. This will enable your army of pest-seeking roundworms to travel into the subsoil using moisture while reproducing at record speeds. Nematodes can eat up to 5,000 bacteria per second. They will colonise the rhizosphere in no time. From here, you can add the subsequent species so they don't compete with each other, instead forming several lines of defence. By doing so, your soil will become much more alive and productive.

One thing to keep in mind is that UV light from the sun does damage nematodes considerably. Avoid spraying them during the daytime. Even indoors, metal halide lamps can give off considerable amounts of UV-A, UV-B, and also trace amounts of UV-C. It is therefore advisable to inoculate your soil at sunset to give the nematodes plenty of time to travel deep into the rhizosphere.

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