Nematodes, The Organic way to Fight Pests.

by Alex Robles

Pests love to build their home and lay their eggs in warm moist places and it’s not just one type.  There are lots of little assassins out there that would love to live in the environment that we build.  A huge part of my IPM (integrated pest management) starts with my soil since it’s going to be wettest part of my grow.  I believe that having a healthy soil is part of having a healthy plant.  When I talk about healthy soil I mean soil that’s alive with beneficial microorganisms that are going to be my foot soldiers against the invaders.


The best methods that I’ve found to control the soil dwelling pests organically is by controlling how wet the top layer of my soil is.  I consider the top layer of my soil to be the first inch to inch and a half.  The longer that top layer stays wet or moist the more inviting it is for pest like fungus gnats to lay their eggs and set up the next generation with a nice place to live.  When I water and feed my plants using a SIP or a wicking system, it drastically cut down the amount of pests that are active in that top layer.  That’s because these techniques let the plant take up the water from a reservoir at its own rate and since it feeds from the bottom up that helps keep that top layer drier.  There are lots of different ways to use these methods and the internet is full of videos and community groups that are dedicated to this type of gardening.

The way that I’ve put this system to work for me is simple, I put the potted plant in a drip pan and filling the pan with water/nutrients.  The drip pan acts as a reservoir and I’ve found that this is the best way for me to water 1gal-5gal pots.  I may need to fill the pan more than once during the same watering to make sure the plant gets enough of what it needs, depending on the size of the pot.  This system can always be scaled up with a few changes for bigger containers.  Now I know some of you are saying “great my ladies are in the ground, what do I do?”  You’re right, this isn’t going to help you, but there’s something else that I do to keep pests numbers low in my soil that might.  I use beneficial nematodes to do a lot of the dirty work for me also.

Rocket Pot with empty drip pan
Rocket Pot with full drip pan

Beneficial Nematodes

Nematodes are microscopic, non-segmented roundworms that happen naturally in the soil but I always like to add more.  They are extraordinarily lethal to many insect pests that have larval or pupal stages of life in the soil. Even though they’re deadly to soil dwelling pests, they are completely harmless to humans, animals, plants and earthworms.  Unlike some chemicals, nematoads don’t cause: residues, groundwater contamination, chemical trespass.  When these little critters are released into the soil they have a search and destroy type of hunting strategy for delicious pests.  The simplest way I can explain it is like this.

A  juvenile nematodes that carry a specific bacteria will move through the soil picking up on the heat and CO2 that the larvae and pupae give off.  When they find a host, they get into them through different openings (nose, mouth, anus) or they’ll go right in through the skin and get into the body cavity.  Once inside, a symbiotic bacteria is released from the nematode gut, which multiplies and causes insect death within 24-48hrs. The nematodes will feed on the bacteria and liquefied host.  During the next few days the nematode will mature and reproduce inside the host. The life cycle is completed when hundreds of thousands of new infective juveniles burst out of the host in search of fresh pray.

Image courtesy of BioLogic

Growers Note:   Nematodes move through the soil best when it’s moist.  Moist not muddy, don’t get carried away and over water.  I also release them at sunset because the UV from direct sunlight is harmful to them and it gives them all night to get established under the surface.


The three main types that are used to fight soil dwelling pests are Heterorhabditis Bacteriophora, Steinernema feltiae and  Steinernema carpocapsae.  Each one of these different species attacks different pest but will sometimes overlap and affect the same pests.  These groups of nematodes kill mostly pests and are safe to use around people, pets, earthworms, ladybugs and other beneficial insects.

Below is a short list of the different pests that each nematode helps control.

  • Heterorhabditis Bacteriophora: Ticks, Ant Queens, Adult Fleas, Asparagus Beetle, Banana Moth, Banana Weevil, Berry Root Weevil, Grape Root Borer, Humpback Flies, Leafminers, Colorado Potato Beetle, Gall Midges, Grubs, Root Weevils.
  • Steinernema Carpocapsae:  Black Cutworm, Caterpillars, Cockroaches Bluegrass Weevil, Cutworm, Flea Larvae,Fly Larvae, Fruit Flies, Large Pine Weevil, Mint Flea Beetle, Mint Root Borer,Mole Crickets, Tobacco Budworm, Webworms, Wireworm, Wood Borers.
  • Steinernema Feltiae:  Beet Armyworm, Black Cutworm, Cabbage Maggot, Corn Earworm, Fungus Gnats, Onion Maggots, Pill Worm, Raspberry Crown Borer, Root Maggots, Shore Flies, Subterranean, Termits, Sweet Potato Weevil, Ticks, Tobacco Cutworm

Inoculating the soil

Since I grow in soil, in containers, I reuse it.  To me throwing away soil seems like a waste. Instead of throwing it away I’ll just put it in a pile and amend it to bring it back to a healthy level.  A couple of weeks before I’m ready to reuse that dirt I’ll inoculated (treatment to produce immunity against a disease or pests) by spraying it with nematodes.  That’s going to help knock down the number of soil dwelling pests that are active in the soil.

When I do this first treatment, I like to use the Arbico Triple Threat Beneficial Nematodes because like the name says, it’s going to have all three of main species that I want.  It’s also really easy to apply, all I do is put the nematode media into a hose end sprayer and spray the dirt mound.  The only downside is that it’s a three part which means I have to apply each one  separately, so i’ll usually wait a couple of days between each application.

Arbico Triple Threat Beneficial Nematodes
BioLogic’s Scanmask Topdressing nematoads

Sometime I’ll have to treat the soil that’s in an active grow for fungus gnats or gypsy moth larvae.  For this I like to use BioLogic’s Scanmask Topdressing because the nematodes are embedded in vermiculite which makes it simple to use.  There are a couple of different ways I can apply it but the easiest way for me is to top-dress the plant that has the problem.  I add 1tbs to the top soil and make sure to completely cover it with dirt because of the damage the UV will cause the them.  Then I’ll water it to help the nematodes establish themselves in the dirt and get to work.

My IPM starts with my soil because if I don’t take care of it, it won’t take care of my plants.  I know that sounds really cliche but it’s true.  So if you’re looking for a more organic, natural way to control pests in your garden, try using nematodes.

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