Are predatory insects haunting your garden? While there are many species of beneficial nematodes, insecticidal nematodes are naturally occurring microorganisms that live in the soil and feed on insects. There are different types of nematodes that can kill insects. However, many of them are difficult to produce on a large scale or have a very narrow host range.
The beneficial nematodes we will discuss here are entomopathogenic nematodes. The term is derived from the Greek word entomon or insect and pathogenic or disease-causing. What makes these insecticidal nematodes special is that they quickly kill their hosts thanks to the special bacteria that live in their systems.
Unlike nematodes, which you might think parasite plants and animals, these beneficial species are a great help to your garden. Among nature’s wonderful gifts, insecticidal nematodes kill plant-eating pests while ignoring normally beneficial insects.
These fascinating creatures can help control up to 200 different insect species from 100 different families. That’s pretty broad coverage. So, How to Apply Beneficial Nematodes? Here’s what’s in this article.
About Beneficial Nematodes
Beneficial Nematodes provide a safe form of biological pest control for gardens. So safe that the Environmental Protection Agency (EPA) has even abandoned crop protection registration.
Not only are they safe to use around pets and people, but they’re also great for treating soils that are sensitive to common pesticides, such as those near water dispensers.
Unlike chemical pesticides or even biological pesticides Bt, you don’t need any special equipment or even a mask to use these creatures in your garden.
You can use the equipment you already have – hoses and sprayers are no problem for them.
Different Types and Behavior
Here are two types of nematodes that are popular as marketable products for protecting your garden.
The first genus is Steinernema – the most commonly sold insect-protected genus.
The second genus, Heterorhabditis, is more difficult to produce for commercial sale. However, these species are very effective at destroying insects that live deep in the soil, especially pinworms.
They are charming little creatures that go through six life stages.
The first is the egg stage. Next, they go through four juvenile stages, culminating in adulthood.
Those in the third juvenile stage, known as “infectious juveniles” (IJ) or sometimes permanent, are the most resistant to environmental stressors.
This is the only stage of their life cycle where they look for insects to kill, and they are active!
Some people sit and wait for their prey to come. Known as “ambush,” these species are particularly effective against insects that move underground. An example is S. carpocapsae.
Some species of Steinernema will jump up and attack their prey – sometimes up to nine times their body length!
Other species are called “cruisers” because they are so active that they can travel long distances underground in search of prey.
H. bacteriophora is a cruiser. This behavior makes it very effective against immobile pests like white grubs.
Some species, such as S. feeliae and S. riobrave, combine both types of behavior.
Nematodes migrate in water between soil particles and identify their prey by monitoring changes in carbon dioxide levels, temperature fluctuations, and sometimes through trails of excrement.
Once prey is identified, it enters the selected insect through natural openings in its body, such as the mouth, anus, or stomata (the openings used to exhale carbon dioxide).
Species of the genus Heterorhabditis can actually enter the insect’s body through the cuticle when there is no other way to gain access to their prey.
You may have noticed that these guys are very aggressive. Once inside, the different species behave essentially the same.
They release a type of bacteria that lives in the digestive system. These bacteria multiply rapidly and kill the insect within 24 to 48 hours.
Different species have their own special bacteria – Xenorhabdus of Steinernema and Photorhabdus of Heterorhabditis.
The interaction between nematodes and their bacteria is symbiotic, which means that each organism helps each other.
The nematode locates and invades the host, providing a home for the bacteria. In return, the bacteria weaken the insect’s immune system. They also produce chemicals that kill insects.
Another thing bacteria do is release chemicals that are toxic to other microbes. This ensures that the nematodes can stay in their new home filled with nutrient-rich food without having to fend off foreign invaders.
While Steinernema species requires both male and female nematodes to reproduce, Heterorhabditis is hermaphroditic, producing offspring only from females with male and female reproductive organs.
Once inside the host insect, the nematode begins to reproduce. Babies thrive by eating the host insect’s vegetative tissue and dead bacteria.
When the insides of the host insects are eaten and fully utilized, thousands of nematodes emerge in their juvenile stages and start looking for their next meal.
Once you’ve introduced beneficial nematodes into your garden, you can see if they’re effective by digging into the soil for maggots. You want to find discolored maggots.
Heterobacter-infected insects are usually orange-red, while Steinernema-infested insects are usually off-white to dark brown.
The reason these insects develop such strange colors is the pigment residues of the bacteria that grow inside them.
It may seem odd, but you should also smell dead insects. They should not have a bad smell. If so, that means they were killed by other types of nematodes in the soil, not the ones you introduced.
Identification, Biology, Distribution, and Lifetime
Nematodes are usually between 0.6 and 2 mm in length, cylindrical in shape, and have unsegmented roundworm bodies.
Steinernema includes shallower, less mobile species, while Heterorhabditis species are more mobile, moving and foraging as deep as 7 inches underground.
It’s important to remember that they move by moving through the water in the space between the Earth’s particles. They generally move more efficiently in sandy soils than in clay because of the larger pores in the soil.
Clear water is critical to the effectiveness of your beneficial nematode attack plan! Watering before application helps them control pests for the following reasons:
- When the soil is moist, pest larvae move higher in the soil – making it easier for nematodes to attack them.
- Watering can lower soil temperature.
- If nematodes are trapped in rough straw, watering can help them move through the straw.
Next, let’s take a look at the pests these creatures target.
The two Steinernemas most commonly used for pest control are S. feeliae and S. carpocapsae. These species attack insects close to the surface and hunt to a depth of about three inches.
S. feeliae is very effective against pests such as fungal gnats and fly larvae, and also parasitizes some species of caterpillar larvae. This species is most effective in clay or silt soils.
S. carpocapsae attacks moving insects, making it an excellent tool for controlling caterpillar larvae. These prey include voracious pests such as cutworms, armyworms and networms.
S. carpocapsae is particularly useful against soil-surface insects where lepidopteran pests typically inhabit. It works best in sandy soils.
S. riobrave is another commercially available species of this genus. It has an unusually broad host range covering a variety of insect orders and is commonly used to control weevil and mole crickets. This type combines the characteristics of ambush and cruiser.
There are also two types of alien tapeworms on the market, both of which are not picky about soil type. Because these nematodes prey on pests deep in the soil, they are used to control maggots, such as the Japanese beetles that live deep in the soil.
H. bacteriophora is very versatile in its host selection. It can attack caterpillars and beetle larvae. It is also very effective against root beetles.
The other common Heterorhabditis tapeworm is H. indica. The species will also attack a range of insects, including caterpillar and beetle larvae, weevils, gnats and thrips.
Choosing the Right Nematode for Your Climate
While you’ll want to choose the right species to control the specific pest you’re dealing with, you’ll also need to consider the temperature of the soil during the growing season.
Some people prefer hot weather, while others are effective in cooler temperatures.
Those of the Heterorhabditis genus are fans of hot weather. H. indica is particularly heat-resistant and can host insects when soil temperatures are 86°F or higher.
H. bacteriophora is also a warm temperature species and is much less effective in soil temperatures below 68°F.
Species of the genus Steinernema differ in temperature preference. S. riobrave is active in a wide temperature range of 59 to 95°F.
Originally isolated in the Rio Grande Valley of Texas, this species can tolerate even semi-arid conditions.
Among commonly used insecticidal nematodes, S. feltiformis is unique in that it is active at temperatures as low as 50°F.
In contrast, S. carpocapsae is most effective at soil temperatures of 72 to 82°F.
A reality when choosing nematodes to control pests is that while they are very effective over time, their effects are not immediate. The first host insects begin to die 24 to 48 hours after application.
We have to be realistic about the behavior and timing of these useful creatures. Now that they have infiltrated their insect hosts, they feed and reproduce in preparation for the next generation.
They will continue to hunt and remain active unless their food runs out or the temperature is too hot or too cold for them. As with any organic management practice, you should look for details and pay close attention to them.
Don’t be afraid to get your hands dirty.
Spend some time digging around your garden looking for infested maggots and larvae. Pay attention to what you see. Monitor the beneficial nematodes before applying them, 48 to 72 hours after applying them, and then a week or two later.
This is a holistic approach that will take time to transform your garden. Consider other factors in the garden such as daily soil temperature and how this relates to your results.
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Application and Use
Now you may be wondering how to use these helpful little creatures in your garden! They can be applied to your vegetable garden, ornamental bed, container, lawn or pasture.
While we focus on soil-borne insects, insecticidal nematodes are also sometimes applied to aboveground plants—for example, to eradicate leafminers from plant tissue.
Identify the pest or pests you want to kill and score them based on the behavior of each species we discuss.
For example, are your target pests shallow-dwellers or deep-divers? What soil temperature does the target pest live in? Is the soil dense or sandy?
The size of the area to be treated will affect the number of nematodes you need to purchase. For example, you would buy $5 million to treat 1,600 square feet of land and $50 million to treat an acre.
If your plants are growing in containers or greenhouses, you may need to apply a higher number.
Nematodes are very sensitive to UV light, so you should use them in the morning or evening to avoid direct sunlight.
Night application is especially important during summer when the Earth’s surface may be too hot to survive. Ground temperatures are lower at dusk.
The following lists many insects controlled by commonly used species, but this is by no means an exhaustive list.
After answering these questions, you will have a clearer idea of which nematode species to choose.
Personal Protective Equipment (PPE) Is Not Required
It’s easy to apply these beneficial organisms to your garden. No large protective equipment is required.
You can wear gloves if you like some distance, but they are not required. These organisms are even safer to use than Bt and have no risk of toxicity.
How Do They Look When They Arrive?
You will usually receive nematodes in the form of gels, clays, dry pellets, or sponges filled with water. All of these forms are soluble in water. Just follow the package directions.
If you require organic certification, be aware that nematodes shipped in pellet or clay form may not be certified organic.
If you get a bag of dead bugs, don’t panic! Beneficial nematodes are usually sold in their insect hosts. Mealworms are a common source of commercially available insecticidal nematodes.
In this case, just sprinkle them on the ground where you want them to work and the hatchlings will appear.
Apply when the time is right. Make sure you do your homework and find target pests so these beneficial nematodes have something to eat.
The best time to apply is spring or fall, when most of the insects you are targeting are in the larval stage. You need to keep an eye on the larvae as they are still underground and therefore vulnerable.
For example, fall is the best time to control white grubs such as weevil larvae.
If you have any questions about the life cycle of a target pest, you can always contact your local advisory body and request more information about the pest.
Compatibility with Garden Chemicals
Surprisingly, juvenile insecticidal nematodes are compatible with a wide range of horticultural chemicals. They can even be mixed with most fungicides and herbicides in the tank.
Fertilizers are usually not a problem unless you use fresh fertilizer or a high concentration of fertilizers like urea.
These organisms are even tolerant to many insecticides, including organophosphates such as diazinon, although the common insecticide carbaryl (Sevin) is moderately toxic.
If you’re not sure whether your chemical pesticide of choice is compatible with these organisms, you can wait a week or two before using the insecticide nematodes.
Package labels often contain the information you need to know about which chemicals your chosen type is compatible with.
Irrigation: Keep the Soil Moist
Pay attention to the moisture content of the soil. It’s a good idea to soak it thoroughly before applying.
After application, go ahead and water again to flush any nematodes from the leaves of plants in the area and bring them closer to their target into the soil.
This is especially important when dealing with lawns that have a problem with white maggots. Thick thatch can make it difficult for nematodes to penetrate the soil.
Watering after application helps the organisms migrate through the straw into the soil where the larvae are located.
After you apply them, you’ll want to keep the soil moist for the next few weeks to make sure they stay active and continue to kill those pesky bug larvae! Unless it’s raining, you should water every three to four days.
How to Physically Apply
To use nematodes, you can use a watering can if you are targeting a small area. For larger areas, you can use a pump sprayer, end-hose sprayer, irrigation system, knapsack sprayer, or power sprayer.
The easiest way to use them is with a controlled-dose hose-end spray.
Be sure to stir the beneficial nematodes and water mixture so they are evenly distributed through whatever sprayer you use. Nematodes tend to take root and sprout if not mixed properly.
CAUTION: Be careful when using hydraulic pumps with high internal and shear forces. You can crush your nematodes!
You can get results within two weeks.
After the first application, you should reapply within 7 to 10 days to ensure there are enough insecticidal nematodes to attack your target insect population.
If you still have pests, continue to apply the organisms every 7 to 10 days until the pest population decreases.
Keep in mind that as the insect population accumulates over the years, it may take more than one app to control it.
The likelihood that your nematodes will survive the winter depends on your climate. They can usually survive severe cold. However, prolonged severe frosts will kill them.
Even if you live in a mild climate, you should reapply a freshly purchased batch of nematodes in the spring. You need a lot of them to attack your pests effectively.
How long nematodes can be stored varies from species to species. S. carpocapsae survives well after drying and can be stored at room temperature for several months. However, other species such as H. indica have a shorter shelf life.
Your nematodes should be shipped to you in insulated containers. Often, they can be stored in the refrigerator for weeks or even months. Because they are sensitive to extreme temperatures, make sure they don’t freeze.
And keep them out of the heat! Temperatures above 90°F will kill most insecticidal nematodes, so be careful not to leave them in a hot vehicle or in a sunny location.
Get Growing with Nematodes
Beneficial nematodes can bring huge benefits to your home garden.
Considering your soil type and the soil’s ambient temperature, you have several options to help you target the pests you want to control.
These wonderful little creatures provide great protection for your garden space and are very safe to use around people, other animals and even beneficial insects.
Now that you know how they work, add them to your garden and watch your pests disperse! Have you ever used insecticidal nematodes in your garden? Then tell Answer The Question your experience in the comments.