How to Use Beneficial Nematodes for Pest Control

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Beneficial nematodes look like worms but they work wonders devouring lawn pests

Got grubs, armyworms, or cutworms in your lawn and garden? We’ll explain how to use beneficial nematodes for pest control so you can get rid of these and more than 200 other soil-dwelling pests.

Beneficial nematodes are one of the best organic pest control options out there, and they’re easier to use than you might think. Follow these six steps to get the most out of your nematodes.

What are beneficial nematodes?

If you’re entirely new to the topic of beneficial nematodes, you might think, great, they can kill my pests for me, but what are they?

Beneficial nematodes are microscopic segmented roundworms that occur naturally in soil around the world. There are more than 20,000 nematode species, but the ones used for pest control are entomopathogenic nematodes — aka insect-parasitic nematodes — from the families Steinernematidae and Heterorhabditidae. 

These insect-parasitic nematodes enter the bodies of soil-dwelling pests through openings in the skin, such as the mouth or anus. Once inside, the nematodes release a bacteria that poisons the host pest and breaks down host tissue for the nematode to eat (pretty gnarly, right?). The host insect dies within 48 hours. 

A nematode’s life cycle includes 6 stages:

  • Egg
  • Four juvenile stages
  • Adult 

The third juvenile stage is when nematodes seek out new prey to infect. During this stage, they’re called infective juveniles. 

The nematodes reproduce inside a host’s body, and the young feed on it until they’ve consumed the whole thing. Then, hundreds of thousands of infective juveniles leave that host and move on to hunt down more insect pests, repeating the process over and over again until there are no pests left.  

How to apply beneficial nematodes in 6 steps

What you’ll need

  • Beneficial nematodes (widely available at garden centers and online)
  • Watering can, hose-end sprayer, backpack sprayer, or pump sprayer
  • Large bucket 

Step 1: Wait for the right time

Beneficial nematodes are living creatures, and they’re sensitive to extreme heat (90 degrees and up) and UV rays. So, you should always apply beneficial nematodes in the early morning or evening when the sun is low and the soil is cool. Apply on a cloudy day if possible to minimize UV exposure.

The right time of year to apply nematodes depends on the pest you want to target. Learn about your target pest’s life cycle to find out what time of year it lives in the soil. That’s when you should apply beneficial nematodes, as they only affect soil-dwellers. 

WARNING: Don’t purchase beneficial nematodes until it’s close to the time you’re going to apply them because they have a short shelf life. You can store nematodes in a refrigerator (NOT a freezer) for about two weeks to a month. Once you have mixed beneficial nematodes with water, you can no longer store them. 

Step 2: Aerate and moisten the soil

Nematodes move through your soil to find their prey (the target pest) using the water in the gaps between soil particles. For nematodes to be effective, those gaps must be present, which means your soil can’t be compacted, and it has to be moist. 

Aerate: If you have a heavy soil type (such as clay) or if your soil is otherwise compacted, it might be a good idea to aerate your lawn or garden before applying the nematodes. Aeration loosens the soil so nematodes have space to move around, and it improves the health of your grass and plants, which will help them recover from pest damage. 

Water: Right before you apply the nematodes, water the whole area you’re going to treat. Water just enough that the soil is damp, but not so much that you see pooling on the surface. You don’t want to drown your grass or plants. This moist soil will allow the nematodes to travel, plus the water will lower the soil temperature, which is good for nematode health. 

Step 3: Mix the nematodes with water

Fill your large bucket with filtered water from your sink or refrigerator door. You can use hose water if you run it through a water filter first. You need to mix the nematodes with filtered water because chlorine could kill them. 

How you mix the nematodes with water depends on how they’re packaged when you buy them. Nematodes usually come in a sponge, in dry granules, or in powdery clay. These are the different ways to mix the nematodes, and both are very simple:

  • If nematodes come in granules or clay: Dump the material into the bucket of water and stir using your hands or a handy tool, utensil, or, well, a new paint stir. The granules or clay should dissolve into the water. 
  • If nematodes come on a sponge: Hold the sponge underwater and squeeze it several times to release the nematodes into the bucket. 

There’s no exact recommended ratio for the amount of water to mix with nematodes. The water itself isn’t important — it’s only there to act as a carrying agent to help you spread the nematodes and to help them get down into the soil where the pests are. 

About 1 teaspoon of nematodes per gallon of water is a good guideline to follow, but you may decide on a higher or lower concentration depending on how bad your pest infestation is. The nematodes you buy may come with instructions that tell you how much water to use. If so, always follow the instructions on the package. 

Step 4: Spray or sprinkle the nematodes across your lawn and garden

Fill your watering can or sprayer with the mixture of water and nematodes. Whatever spreading device you use, the openings should be at least ½ millimeter wide so the nematodes can get through. 

Spray or sprinkle the nematodes across the area you want to treat, either your whole lawn and garden or a specific area ridden with pests. Do your best to spread the water and nematodes in an even layer. Shake your watering can or sprayer continually during use because the nematodes are heavier than water and will sink to the bottom if you let them. 

If your sprayer or watering can doesn’t hold enough water to cover the whole area that needs treatment, simply refill it once you run out and keep spraying. Just remember to mix the water in the bucket again before refilling in case the nematodes sank to the bottom. 

This brief video from Natural Insect Control will show you how to mix nematodes on a sponge with water and how to spray them in your lawn using a hose-end sprayer:

Step 5: Keep the soil moist

As we already mentioned, nematodes need a moist environment. Keep the soil extra moist for about 10 days after application while the nematodes establish themselves. During this time, lightly water the treated area every three or four days. 

Since you’ll water so frequently for those first 10 days, you don’t want to use a lot of water, or you might drown your grass and plants. Just a light sprinkling is enough to keep the soil moist and cool for the nematodes. You won’t need to water if it rains. 

Step 6: Reapply as necessary 

You should apply beneficial nematodes at least one more time after the first application. Wait about seven to 10 days, then apply the nematodes again, the same way you did the first time. This second application replenishes the population and ensures you don’t miss any spots. 

You should notice a decrease in the target pest population after about two weeks. If the infestation continues, apply beneficial nematodes again every seven to 10 days until the pests disappear. 

Beneficial nematodes kill individual pests within 48 hours, but it will take about two weeks for a noticeable decrease in pests. The nematodes need time to consume one host and reproduce, then move on to the next one and repeat the whole process over and over again for each pest. 

Choosing the right beneficial nematodes

All beneficial nematode species don’t prey on all pests. Before you buy beneficial nematodes, you have to identify the pest you want to eradicate. Then, find the right type of nematode to target that specific pest. 

The most common types of beneficial nematodes available for sale are:

  • Steinernema carpocapsae
  • Steinernema feltiae
  • Heterorhabditis bacteriophora

The table below shows which of these three species is most effective for controlling some common lawn and garden pests. 

Remember: Different kinds of nematodes control more than 200 pests, so this is not a complete list. If you don’t see your pest on this list, research online or contact a beneficial nematode producer directly to find out if there’s a type of beneficial nematode that would work for you.

If you have this pest…Use this species of beneficial nematode…
ArmywormSteinernema
carpocapsae or
Steinernema feltiae
AntsHeterorhabditis
bacteriophora
BagwormSteinernema
carpocapsae
BillbugHeterorhabditis
bacteriophora
Black vine weevilSteinernema
carpocapsae or
Heterorhabditis
bacteriophora
BorersSteinernema
carpocapsae or
Steinernema
feltiae or
Heterorhabditis
bacteriophora
CaterpillarsSteinernema
carpocapsae
ChafersHeterorhabditis
bacteriophora
CockroachesSteinernema
carpocapsae
CutwormSteinernema
carpocapsae
FleaSteinernema
carpocapsae
Fly larvaeSteinernema
carpocapsae
Fungus gnatSteinernema
feltiae or
Heterorhabditis
bacteriophora
Grubs (beetle larvae)Heterorhabditis
bacteriophora
Mole cricketsSteinernema
carpocapsae
Root aphidsSteinernema
feltiae or
Heterorhabditis
bacteriophora
Sod webwormSteinernema
carpocapsae
Termite (queen)Heterorhabditis
bacteriophora
Termite
(below ground)
Steinernema
feltiae
Termite
(worker
and soldier)
Steinernema
carpocapsae
ThripsSteinernema
feltiae
TicksSteinernema
feltiae or
Heterorhabditis
bacteriophora
WebwormSteinernema
carpocapsae
WirewormSteinernema
carpocapsae or
Steinernema
feltiae

Source: ARBICO Organics

FAQ about beneficial nematodes

1. Where can you buy beneficial nematodes?

You’ll find beneficial nematodes for sale at most garden centers and from major online retailers like Amazon. But be careful where you buy nematodes since they don’t have a very long shelf life. Nematodes are only useful for pest control if they’re alive when you add them to your soil.

For the freshest nematodes, buy directly from the source. Here are some beneficial nematode producers you can buy from online:

2. How many beneficial nematodes do I need?

Different sources suggest different application rates for nematodes. There’s no hard and fast rule. But these rates should ensure there are plenty of nematodes in your soil to tackle pest populations:

Size of the area being treatedHow many nematodes it takes to cover the area
1,600 square feet5 million
3,600 square feet10 million
1 acre50 million
5 acres250 million
10 acres500 million

Remember that you’ll usually need at least two applications of nematodes for effective pest control, so you may need to purchase double the suggested number of nematodes. We recommend waiting to buy the second round until you get close to the second application date so you don’t have to store the nematodes and risk some of them dying. 

If you don’t want to do a second application, try a higher rate of about 25,000 nematodes per square foot. However, applying more nematodes the first time doesn’t guarantee you won’t need to apply again. 

3. How do you tell if beneficial nematodes are working?

About two weeks after applying beneficial nematodes, you should notice a significant decrease in the target pest population. That’s not to say they’ll be completely gone after two weeks, but you should be able to see a difference. 

For more evidence that the nematodes are doing their job, dig up a square-foot section of soil a few inches deep. Look for discolored pests. Grubs and other white-bodied pests often turn orange-red or reddish-brown after being infected by nematodes. 

Note that you won’t find any dead insects as evidence that nematodes are working, as the nematodes completely devour their hosts. 

4. How long do beneficial nematodes last?

Beneficial nematodes can live and prey on insect pests in your soil for up to 18 months after application as long as the ground doesn’t freeze. 

5. Do beneficial nematodes overwinter?

One hard freeze usually isn’t enough to kill off a nematode population, but prolonged freezing temperatures will kill them. So, if you live in an area with harsh winters, you’ll likely have to start all over again with nematodes come spring. 

6. What are the disadvantages of beneficial nematodes?

Beneficial nematodes are natural and effective for getting rid of target pests, but they have disadvantages, too, including:

  • They only work for pests in your soil. They will not harm pests that live and feed on plant leaves (unless those pests have a soil-dwelling stage in their life cycle).
  • Not all species of nematodes work for all pests. You have to identify the pest in your yard and choose the right nematodes, or they won’t work. 
  • They have a limited shelf life, and you have to use them within a month of purchase for the best results. 
  • They may not be effective in some soil conditions, such as dry soils or heavy soils with poor aeration. 
  • Results are not immediate. It takes around two weeks for nematodes to cause a significant decrease in pests and around 30 days for plant health to improve as a result. 
  • The cost can be high. Though one package of beneficial nematodes costs about the same as chemical pesticides, the need for repeated applications can make nematodes more expensive. 

Beneficial nematodes: Deadly for pests, safe for everyone else

Are you reluctant to use insecticides on your lawn and garden for fear of harming pollinators and other beneficial insects? You don’t have to worry about that with nematodes. Nematodes only target specific insects and have no effect on others. 

Beneficial nematodes are also perfectly safe for pets and people. They’re harmless to all mammals, birds, reptiles, amphibians, and aquatic life. They won’t damage your plants or grass, either. 

Beneficial nematodes are so safe as a means of pest control that the Environmental Protection Agency (EPA) doesn’t even require registration for their use. You can apply beneficial nematodes to your lawn and garden with total peace of mind. Only the pests need to worry. 

Need help keeping your grass and plants pest-free? Reach out to a local pest control company today. And lean on Lawn Love’s local pros for all your other lawn care needs, including mowing, fertilization, and weed control.

Main Photo Credit: CSIRO | CC BY 3.0 | via Wikimedia Commons

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