Nematodes, excellent to target pests directly – and naturally!

Nematodes for pest control

Every gardener has that dreaded experience: beautiful cabbage, lettuce, or carrot crops destroyed in mere days by some horrible pest. A blitzkrieg of unwanted insects such as chafer beetle larvae , black vine weevil larvae, potato beetles, and other cabbage worms, not to mention slugs and snails, can annihilate several weeks of work. Luckily, biological control against these veggie garden pests include nematodes which are particularly effective. What are they? What is their role? Why and how should you use them?

Everything to know about nematodes

Bad nematode symptoms
Ravages caused by phytopathogenic nematode (plant parasite nematodes)

Nematodes are microorganisms that are naturally present in the soil. They’re completely invisible because of their near-microscopic size. They measure between 0.1 and 3 mm and look like worms.

There are thousands of types of nematode. Some infect humans or animals, and others target plants. Plant-attacking “phytopathogenic” nematodes, such as gall nematode, attack either above-ground portions of the plant, or tubers and roots instead. They particularly love infecting vegetable plants like tomatoes or potatoes.

However, in this article, we will focus on beneficial nematodes that are great allies to us as gardeners.

  • Indeed, there are nematodes that are phytophagous: they feed on organic matter, accelerating its breakdown to release useful nutrients (great to activate your compost!).
  • Others are entomopathogenic, meaning that they infect and kill those insects that shamelessly target our fave vegetables.

They are effective allies that are completely natural and are classified as organic and biological control. Let’s not forget, that these biological control methods involves natural predators to combat pests in vegetable gardens and ornamental gardens.

How do nematodes act in vegetable gardens?

Description of a nematode
Nematodes: tiny microscopic worms that live in soil

These tiny worms infect harmful insects. They so small they can enter through the insects natural orifices (mouth, airways, joints…). Once settled in, they unleash a symbiotic bacterium that kills the host insect. It is inside the carcass of this harmful insect that the nematodes reproduce and create a new generation. The cycle continues as these infest other members of the pest insect family. This cycle continues until complete extermination of the pests, as nematodes only reproduce when a host is present. When it’s over, they naturally disappear.

It is worth noting that these nematodes are non-toxic to humans, animals, and the environment, unlike pesticides and insecticides. They act quickly, within 24 to 48 hours, and leave no residue on the plant, even if it is blooming.

The different types of nematodes

There are different types of nematodes on the market these days. They’re for biological control, highly specific to the prey they infect:

  • Good nematodes help control pests
    Steinerma feltiae nematodes kill wireworms

    Heterorhabditis bacteriophora (Hb) against strawberry and grapevine root weevil, chafer beetle, box tree moth, beetle, crane fly, white and gray grubs, black vine weevil larvae

  • Heterorhabditis megidis (Hmeg) against strawberry and grapevine root weevil
  • Steinernema carpocapsae (Sc) against wireworm, strawberry, root, and grapevine weevils, cabbage worm, box tree moths, crane flies, palm tree leaf moth, mole crickets, Colorado potato beetle, webbing caterpillars
  • Steinernema feltiae against fungus gnats, vegetable and orchard caterpillars, wireworm larvae

These nematodes are commercially available. They come in the form of a powder or gel that is diluted in water. In the gel or powder, they’re dormant, waiting to be activated. It is essential to follow the dosage and preparation instructions provided by manufacturers for them to be fully effective.

When to use them?

When applying nematodes, a few rules should be followed:

  • How to apply nematode
    Spray nematode in humid weather

    Each nematode has an optimal temperature range, usually between 10 and 33 °C

  • Better carry out the spraying on a cloudy day or in the evening, as nematodes are very sensitive to light and UV rays
  • The application of nematodes is best done in spring and summer, when insect pests are active and present
  • Spray nematodes on your plants during humid weather. If it hasn’t rained, it is necessary to water soil well before spraying. This allows nematodes to move around more effectively as they hunt their hosts. Both foliage and substrate should be kept moist after application.

How to apply nematode

Nematodes can be applied to foliage, branches, or soil depending on which insects you’re targeting. Apply nematodes using a sprayer or watering can, immediately after diluting the product in water. No protective equipment is necessary for these sprays.

Images: CC BY 2.0: F. Delventhal, Philippe Garcelon, Katja Schulz; dreamstime: Welcomia; Public Domain: Scot Nelson