Beneficial Nematodes 

Beneficial Nematodes

by: Allen Buchinski

In my previous article, I discussed “what are nematodes” with a focus on plant parasitic types. Here we’ll focus on the beneficial kind.

As you surely remember, nematodes are tiny round worms that proliferate in nature. Of all nematodes, only a portion cause problems in your garden, these types live on or in plant tissue, disrupting the plant’s natural processes. There are many other nematodes that feed on other things, including organic matter in the soil, bacteria, insects, even animals. It’s the insect eating variety that’s of interest to us here, harnessing them to help us with insect pests in the garden.

How Do They Work?

Since nematodes live in the soil, they can be used against insects that spend at least part of their lifecycle underground, typically the larvae form (although researchers are also exploring the methods for applying nematodes above ground as well by timing the release in such a way that they can enter a host insect before succumbing to the elements.) There are two strategies used by nematodes for finding prey, depending on the species:

  • One type, called “ambusher”, remains stationary in the ground, waiting for an insect to pass by,
  • The other, labeled “cruiser”, travel through the soil in search of prey, using techniques including following excrement trails and reacting to changes in temperature and carbon dioxide levels.

In order for nematodes to be available commercially, they must be able to be mass produced and shown to be effective against insect pests. Currently, there are about five varieties produced for sale, grown for use against root weevils (including the black vine weevil), cutwowrms, fleas, ants, termites, grubs and more. They’re available from many garden suppliers and can be purchased by mail order.

Buying and Using Them

Because beneficial nematodes are live animals, it’s wise to buy them from a reputable supplier. They must be handled carefully before application and in order to increase the chances of buying viable nematodes, consider buying them direct from the manufacturer.

To give you an idea of selection, Peaceful Valley Farm Supply sells different varieties in quantities ranging from a vial, to a pint, and for commercial growers, packages containing up to 500 million nematodes (with instructions indicating that heavily infested areas may require as much as 1 billion/acre per application. (Ummm, hello, Peaceful Valley? I just received my order and I think I only received 497 million, where are the other 3 million?)

Nematodes are supplied in a concentrated form, often on a wet sponge
that you’ll mix in water and apply using common types of liquid
applicators. Keep in mind that nematodes are most effective in soil
temperatures above 60 deg. F. Some tips for use:

  • When you buy them, use them as soon as possible, and store
    them in a refrigerator if you can’t use them right away (but be careful
    they don’t freeze)
  • Apply them in the early morning or evening
    to give them the best possible chance of survival. Remember that
    ultraviolet light and heat will kill them
  • Water them into the
    soil after application. This helps move them into the soil, gets them
    away from harmful sunlight, and gives them moisture necessary for
  • Be careful about using chemical pesticides and
    nematodes at the same time, or one shortly after the other. Some
    pesticides will kill nematodes, if you need to use them, either don’t
    apply nematodes or check to see if it’s safe
  • Above all, follow directions carefully!


Keep in mind that you’re not going to see the nematodes work. And even if they are effective, the evidence will be underground. As a rule of thumb, wait at least 2-3 weeks for positive results. The best method for tracking effectiveness is to observe the levels of the insect to be controlled, but remember that you’re targeting the next generation of insects, so take the insect life cycle into account when you observe (hey, no one said it would be easy!)

And Finally

While not as common as many other pest control techniques, nematodes deserve a look in many situations. But keep in mind that any pest control strategy essentially aims to alter nature’s own balance (even though it may seem as if things are out of balance). And while you may “win” in the short term, Mother Nature almost always prevails in the long term. With nematodes, this means that your application will have a limited life span, and if the problem persists, you’ll need to reapply (again and again in some cases.) Because of this, remember your IPM basics, think about cultural and environmental controls first and limited biological controls such as nematodes after that.

Revised: 02-Mar-2003

Source: Beneficial Nematodes | Master Gardeners of Santa Clara County

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