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Nematodes UK – How, Why & When to use on leatherjackets, grubs & ants

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The word nematodes is used a lot in lawn care and even gardening. But there’s a specific time and place when they are most effective.

That’s why I’m writing this article. To help you know when to use nematodes and how to use them so they are most effective.

So, what actually are nematodes?

Ultimately, Nematodes are a 100% organic way of controlling pests in your garden. They are a type of parasitic ringworm. They’re fatal to many pests found in and around the garden and in particular our domestic lawns.

Essentially they will kill a pest by releasing bacteria into it’s body before eating it up. Lovely eh?

They are readily available from many websites but like with most garden products, the amount you use over a specific area is important. So be sure to follow the instructions carefully.

Myth Buster

Nematodes aren’t harmful to humans. They also aren’t harmful to animals such as dogs and cats. They only attack insects.

Store them properly

Nematodes are living organisms and need to be treated like one. When you buy them they’ll have an expiry date – normally around 2-3 weeks. They also need to be kept in the fridge

What insects in the soil can Nematodes kill?

  1. Leatherjackets:The specific nematode species commonly used to target leatherjackets are Steinernema feltiae and Heterorhabditis bacteriophora
  2. Chafer Grubs: Nematodes like HB (Heterorhabditis bacteriophora) and SC (Steinernema carpocapsae) are effective against white grubs, which are the larvae of beetles such as Japanese beetles and June bugs. White chafer grubs can damage grass roots and cause brown patches in lawns.
  3. Cutworms: Nematodes can be used to control cutworms, which are moth larvae (they look like caterpillars) that cut down young plants at their base. Steinernema feltiae is one species that can target cutworms.
  4. Turf Webworms: Nematodes like SC ones can help control turf webworms, which are the larvae of lawn moths that can damage grass by chewing on the blades.
  5. Armyworms: Armyworms are known to feed on grass and other plants. SC and SF can be effective against armyworms.
  6. Billbugs: Billbugs are weevils that can harm grass by feeding on roots and stems. Nematodes like HB are used to manage billbug populations. They are generally found in Kentucky Bluegrass, which is less common here in the UK
  7. Flea Larvae: Flea larvae can be a problem in lawns, and SC can target them.
  8. Ants: Some nematode species can help control ant populations. SC is one example that can be effective against ants.

The best time of year to use them on different grubs

Some pests need treating at specific times of year for nematodes to be effective. You can’t just apply them willy-nilly. Others can be treated as soon as you find them.

You also need to apply them on moist soil. If the ground is dry they won’t be as effective. What’s more, I recommend watering them in straight after application. That way they’ll be able to work their way into the soil to find their prey.

So, let’s take a look.

When to use nematodes on leatherjackets or chafer grubs

The best time to treat leatherjackets or chafer grubs is in Autumn. But this is where a lot of people get it wrong.

What happens then?

People go out to their lawn or garden in Spring only to find that some of their grass has been completely ruined. There may even be blackbirds pecking at the soil – which is a very good sign.

A sign that you have grubs in the lawn.

So, you go outside to check and find either leatherjackets or chafer grubs. Or even one of the other pests mentioned above.

There’s one problem – it’s way too late to apply Nematodes in Spring.


Because the lifecycle of leatherjackets means they are the smallest in the Autumn – when the eggs are laid. By the time it gets to Spring, they have grown nearly to full-sized daddy-long-legs and when they are at this size, the nematodes can’t infect them with enough bacteria to kill them off.

When to use nematodes on Ants

Nematodes can kill ants too!

I’ve written a full article on how to properly remove ants from your lawn, which gives methods other than Nematodes, such as using coffee grounds and could be more effective.

That said, there is a time and place for nematodes to be used against ants. That is between April and September when the ants are most visible on the top of the soil.

They should also be used on moist soil or turf to be most effective.

If you have a stubborn ant problem in your grass, then you should apply them 3 times, every 4 weeks.

Note: They won’t kill ants

The ants won’t be killed during this process but will decide to move their nests away from the area. With that in mine, it’s useful to apply nematodes to a larger area than just focusing on the ants nest.

For example, treat the area of 50m2 around the ants nest.

The best conditions for applying Nematodes

Temperature and moisture levels are important factors during application. Mainly because these can affect nematode activity.

Follow the recommended application conditions for best results.

CheckIdeal Rationale
Soil TemperatureNematodes are most effective when the soil temperature is within the range of 13°C to 29°C (55°F to 85°F)Nematodes are more active and can seek out and infect their target pests within this temperature range.
Extreme HeatAvoid applying nematodes during extremely hot weather or when the soil temperature exceeds 37°C (100°F)high temperatures can reduce nematode viability and effectiveness
Extreme ColdAvoid applying nematodes when the soil is frozen or when temperatures are significantly below their optimal range.They may become dormant or die in very cold soil.
Time of DayIt’s often recommended to apply nematodes in the evening or early morning when temperatures are cooler and there is less direct sunlight.It can help prevent desiccation (drying out) of the nematodes
Moisture LevelsEnsure that the soil is sufficiently moist but not waterlogged when applying nematodes.Adequate soil moisture is essential for nematode survival and activity.

Are Nematodes pet and child friendly?

Yes, parents and children can use the area immediately after application. As we’ve seen above they are only infectious towards small insects and even have a hard time affecting affecting mature larvae.

How many Nematodes to apply in one application

As we’ve seen above, these are microscopic creatures and that means you need a lot of them to make an impact.

As an example, a 100m2 pack contains around 50 million worms. I know, that’s a heck of a lot!

Usually, all 50 million worms (one pack) are mixed with 5 litres of water in a bucket, then 500ml of this solution gets mixed with another 5 litres of. This then treats 10m2 of lawn.

If you have a stubborn problem, then you can increase the application by double. So, instead of treating 10m2 with the final solution, treat 5m2 instead.

That way you’ll have more worms concentrated in that part of the lawn.

Remember though, a pack that shows 100m2 will only treat 50m2 if you double up the application rate.

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