Use Beneficial Nematodes to Reduce Bad Bugs in Your Garden

While there are many types of beneficial nematodes, insecticidal ones are naturally occurring microscopic organisms that live and feed on insects in the soil.

A collage of two photos, one of a microscopic nematode and the other of two dead grubs killed by nematodes.

There are different types of nematodes that kill insects. However, many of them are difficult to mass produce or have very narrow host ranges.

Beneficial nematodes attack unwanted insects while they are in their larval phase, dwelling in the soil. These types can be applied to your garden or lawn to help fight predatory insects that are creating problems for you!

They are a great alternative to conventional pesticides and are completely safe for the environment because they are naturally occurring. They can help control up to 200 different species of insects in 100 different families.

That’s definitely a wide range of coverage!

Let’s talk more about what they are before we get into how you can use them, and where to buy them.

Benefits

Nematodes are so safe that the EPA (Environmental Protection Agency) waived them from needing to be a registered product for pest management, because they occur naturally and do not demand any kind of genetic modification or manipulation.

They are an amazing alternative to conventional pesticides, and they are safe for use around your kids, your pets, and the beneficial insects in your garden like earthworms and ladybugs.

The effects of nematode applications occur over time rather than setting in immediately. The first host insects will begin to die within 36-48 hours.

Once they begin feeding and mature, the nematodes will begin reproducing. They will continue to hunt and stay active in your garden, unless they run out of food or experience a temperature interruption.

Can Nematodes Control Moles?

Yes, they sure can… although not directly. Moles feed mostly on grubs and other larvae. Since these helpful beneficials eliminate their food source, moles will no longer have any reason to move in or stay.

Different Types and Behavior

Nematodes are usually between 0.6 and 2 millimeters long, with a cylindrical shape and an unsegmented roundworm body.

There are several species from two specific genera that are commonly sold to protect your garden.

The first genus is Steinernema. These multiply easily, and are the type most commonly sold for insect protection.

The two most popular species of Steinernema available commercially are S. feltiae (Sf) and S. carpocapsae (Sc). These species attack insects that are closer to the surface, hunting in the area between 0 and 3 inches deep in the soil.

S. feltiae is a good species for attacking shallow pests and is slightly more active than S. carpocapsae, making it a bit more of a mobile hunter – but not as mobile as Heterorhabditis bacteriophora (Hb), which we’ll touch on in a minute.

S. feltiae is also adept at eradicating pests like fungus gnats, and fly larvae. This type is the most tolerant of cooler temperatures among those available for beneficial use in the garden.

Now, within the same genus but a different species, let’s look at S. carpocapsae. This variety is less mobile, but is a great tool for attacking caterpillar larvae!

The second genus, Heterorhabditis, and more specifically the species H. bacteriophora (Hb), is more difficult to produce for commercial sale. But this type is highly effective for deeper dwelling insects, especially grub worms and beetle larvae such as those produced by the Japanese beetleH. bacteriophora can penetrate up to 7 inches into the dirt.

Identification, Biology, Distribution, and Life Cycle

Nematodes are incredible little creatures with a somewhat morbid means of survival. They have six stages of life.

Their first of these is the egg stage, followed by four juvenile stages, and finally, the adult stage. Surprising as it may sound, the adults spend their entire life inside the body of a host insect.

Top down view of an image of a cluster of microscopic ground dwelling nematodes.

In the third juvenile stage, the nematode is called a “dauer.” Dauers are the hunters. Some sit and wait for prey to pass by (typically the habit of those in the Steinernema genus) while the Heterorhabditis types will actively move through the soil while hunting.

Nematodes travel in the water found between particles of soil. Too much water may drown them, while too little will limit their ability to move. So, if you’re using these savvy guys as a part of your pest management program, keeping the moisture level in your soil at an even level is critical.

Also note that if your soil is too dry or too constricted and dense, introducing beneficial nematodes may not be a realistic option to incorporate into your plan just yet. Work to solve those problems first, then apply them to the soil.

Micro shot of a ground-based beneficial nematode.

Fascinating little creatures, they identify their prey by monitoring temperature, carbon dioxide levels, temperature variations, and excrement trails.

Most varieties attack grubs or larvae, but Heterorhabditis can penetrate the hard shell body of an adult insect if there are no other prey options.

Once they identify their host, they enter its body through natural openings like the mouth, anus, or spiracles, openings that are associated with respiratory function.

Once inside, they release a toxic bacteria, Xenorhabdus sp, and begin reproducing while their host is dying.

The bacteria will proceed to kill the insect within the course of approximately 24-48 hours, via blood poisoning.

Their young grow by eating the nourishing tissue of the host insect, killing it in the process, and mature through their juvenile stage. They will then leave to go hunt for more tasty insects to attack.

Nematodes have varying life expectancies, approximately 15 weeks for S. carpocapsae, 20 weeks for S. feltiae, and 8 weeks for H. bacteriophora.

They will reproduce readily, but they may end up doing too good of a job of this, exhausting their food sources and dying off in several years. This will allow new herbaceous pests to invade. You may want to spray additional applications every year or up to every three years, depending on insect pressure.

Steinernema species need representatives of both male and female sexes to be present reproduce, while Heterorhabditis species are hermaphroditic and produce offspring solely through females who have both male and female reproductive organs. Once the worm is inside its host’s body, it begins to reproduce.

A scoop of garden dirt showing dead beetle larvae killed by nematodes.
Nematodes infiltrate their hosts’ bodies during the larval stage, as evidenced by these dead beetle larvae.

If you are using beneficial nematodes in your garden, an interesting way to see if they are being effective is to dig through your soil looking for grubs.

You want to find grubs that are discolored (usually orange-red or reddish-brown) and do not have a putrid smell. This means that the worms are doing their job!

Application and Use

Now you may be wondering how to use these magical little critters in your garden! Good, let’s get practical.

Beneficial nematodes can be applied to your vegetable garden, ornamental beds, containers, lawn, pasture… you name it! Identify the pest or pests you’d like to work at disturbing, and evaluate which may be more apt to use based on the behavior of each species we’ve talked about.

Micro photo of a beneficial ground dwelling nematode.

For example, is your target pest a shallow-dweller, or a deep diver? What temperature is the soil where your target pest is living? Is there enough moisture to apply them, or should I water down the soil before applying? Is the soil compacted?

Insect Control by Nematode Type

Required Personal Protective Equipment (PPE)

Adding beneficial nematodes to your garden is simple. Like I mentioned before, they’re naturally occurring and don’t pose a danger to your family or your pets. One of my favorite things about the process is that you won’t look like a moon walker on a space mission when you’re moving around in your yard!

No big rubber gloves up to your armpits or masks covering your nose, making you feel claustrophobic. Also, no sticky hazmat suit required.

If you prefer a little distance, you can absolutely wear gloves, but this is not essential. Obviously, you don’t want to slosh the mixture all over yourself or let your dog lap it up straight out of the bucket, but beyond that, there’s no potential toxicity or accidental contamination to worry about here if used as directed.

How Do They Look When They Arrive?

Usually you’ll receive your nematodes in the form of a gel, dry clay, granules, or water-filled sponges. All of these forms will dissolve in water. The sponge form requires squeezing to release them.

Nematode Application Rates

Before you apply them to your garden, you can test to make sure they are alive and active by applying them to a small test batch of grubs in some soil with a little water. Make sure the bucket containing your test materials is set in a dark, cool place where the worms won’t die!

Timing

Apply when the time is right. Make sure to do your homework and identify your target pests with certainty so the beneficial nematodes will have something to eat.

The best time to apply is in the spring or fall, when most of the insects you’ll be targeting are in their larval stage. That’s when the nematodes can attack them, while they’re in the soil. Targeting grubs in the fall is ideal.

If you’re in doubt about the life cycle of your target pest, you can always reach out to your local extension agency and ask for more information on the specific pest in question.

Another important consideration is temperature. Optimum temperatures for applying these beneficials are as follows: 70-83°F for S. carpocapsae (can tolerate down to 60°F), 70-79°F for S. feltiae (can tolerate down into high 50’s), and 79-83°F for H. bacteriophora (can tolerate down to 65°F).

Another important thing to note: UV light will kill the nematodes. Apply at dawn or dusk, when sunlight is not direct.

Do not apply within two weeks of applying fertilizer to your garden. High nitrogen levels can pose a threat, and possibly kill them.

If you are still using pesticides in your garden to control some other type of pest, check your labels to see if the pesticide is toxic to invertebrates such as worms.

Before Applying

Pay attention to the moisture content of your soil. If you need to, give it a good watering before you apply. After you have finished, go ahead and water again to rinse them down into the soil closer to their target.

After you’ve applied them, you want to keep your soil moist for the next couple of weeks, to make sure they stay active and keep killing those pesky insect larvae! Water as needed every couple of days if you don’t receive rain in your area at this time.

How to Physically Apply

To apply, you may use a watering can, pump sprayer, end-hose sprayer, irrigation system, backpack sprayer, or motorized sprayer.

Remember to remove any restrictive sieves that may be in the nozzles of your sprayers! The easiest way to apply them is by using a hose end sprayer that controls the dose applied.

Bottom half of a person in a potato patch using a backpack sprayer to distribute nematodes.

Make sure to agitate the mix of worms and water so that they are evenly dispersed from whatever sprayer you are using.

Again, remember to avoid direct sunlight, extreme cold or hot temperatures, and fertilizer or pesticides that may kill nematodes.

Noticeable Results

You should see results within 2 weeks. Nematodes need time. Do your scouting and keep a journal to note the changes you are seeing.

Monitor the insect load before you apply your beneficial nematodes, 48-72 hours after you’ve applied them, and then a week or two later.

As with any organic management practice, scouting and close attention to detail should be given. Don’t be afraid to get your hands dirty (if you’ve read this far, I doubt that’s a fear of yours!).

Editor’s Note

About four years ago, I sprayed my parents’ curtilage with all three of these commonly available types of nematodes, but I was really targeting fleas and ticks. This consisted of around four acres of mixed brush, trees, and open areas in north central Missouri. Their dogs had horrible flea issues that Frontline wouldn’t touch, and they had tried everything from peppermint oil to Sevin dust dips.

There really wasn’t a noticeable difference during the first year, but I applied them late in mid-summer, during a period with plenty of rain. For the past three years, fleas have not been an issue… and neither have Japanese beetles, and a whole host of creepy crawlies that used to damage their vegetable patch, mini-orchard, and berry bushes!

— Mike Quinn

Spend some time digging in your garden, looking for infected grubs and larvae. Note what you see.

You’re looking for discolored grubs and insect larvae that have turned from whitish beige to rusty red or brown.

This is a holistic approach that will take time to create change in your garden. Note other factors in the garden like soil temperature, and how that correlates with your findings.

Reapplication

Depending on pest pressure in your garden, you may need to apply a second round 1-2 weeks after the first application. And you may need continue to reapply beneficial nematodes each year, depending on pest numbers and winter conditions.

An older gentlemen applies beneficial nematodes with a backpack sprayer.

During winter, they will go dormant in your lawn and garden. But a percentage will be lost depending on the severity of your winter. If you want a head start on certain pests, you’ll need to reapply a new batch the next year in early spring – particular in cold, northern climates.

Storage

Nematodes purchased for beneficial use in their various forms can be stored in the refrigerator for up to two weeks, but using them immediately is ideal.

Get Growing with Nematodes

Beneficial nematodes can offer your home garden immense perks!

Have a beetle problem?  There’s a species that will fight it. Have a fly problem?  There’s a variety for that, too!

You name the pest, and if it has a phase of life that takes place in the soil, there’s probably a nematode that can manage it.

These wonderful little creatures offer great protection for your gardening spaces, and are totally safe to use.

Grab your shovel and your journal, and head for the garden! We’re going to hunt for grubs and give them some competition.

© Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Product photos via Arbico Organics. Uncredited photos: Shutterstock. With additional writing and editing by Mike Quinn and Allison Sidhu.

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About Alexis Morin

Alexis Morin is an avid gardener who resides on and manages a horse ranch in north Texas. She holds a BA in English literature with a minor in horticultural sciences from Clemson University, and she loves to read, write, and garden. If Alexis is not in a pasture learning the names of all the growing green things, you can find her in her garden growing fruit, veggies, and flowers. Alexis once managed a sizable CSA operation in Valley Center, Kansas, and her specialization is in growing high quality organic vegetables. She believes that soil, like food, brings people together!

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Cindy
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Cindy

I always thought they were bad!! Are there bad ones? I was told not to plant tomatoes in the ground here in SWFL, because they eat the roots? I’m confused now, thanks.

Mike Quinn
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Mike Quinn

Hi Cindy, their like many other critters (i.e. beetles), some types are good and some types are bad. The ones you are referring to are root-knot nematodes which are plant-parasites and are distant cousins of the beneficial insect-parasitic worms covered here.

Cindy Carlson
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Cindy Carlson

Thanks for responding! Is there a way to get rid of these bad ones,or do I continue to plant only in pots?

Allison Sidhu
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Allison Sidhu

You’ll need to pull up and destroy infested plants, paying particular attention to getting all of the roots out of there. Depending on your location, one of the best ways to get rid of them is to expose root-knot nematodes to extreme heat or cold. Till and turn the soil periodically in the hot weather, and through the winter after the first frost date in your area. Wait to apply beneficials until the return of warm weather, and don’t plant anything new in the area until you’re sure they’re gone. We’ll cover this topic in more detail in a future… Read more »

Kim
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Kim

Hi! These critters are currently feeding in the roots of my new plants. I believe they are wire worms. Can u tell me if using beneficial nematodes at this stage will eradicate them?