Nematodes for Slugs & Snails: Are They Really a Good Idea?

Do nematodes help against slugs and snails in the garden?

You will find information here about the advantages and disadvantages of this method, as well as general information about the application of nematodes to control slugs.

Nematodes kill slugs from the inside.

What are nematodes? How do they work as slug control?

Nematodes are roundworms. It is estimated that they represent over 80% of the total number of multicellular animals on Earth.

This makes them by far the most species-rich organisms on the planet.

They are almost everywhere, in the water as well as in the ground. Around 20,000 different species have been identified to date.

Some nematodes also live as parasites in slugs. They are called phasmarhabditis hermaphrodita (ph for short) and are used to control slugs in organic farming.

These beneficial worms live in the ground and penetrate a slug’s body via its respiratory opening (mantle cavity).

There, the nematodes secrete bacteria, which then decompose the slugs from within. The killing process is not yet entirely understood, however.

Some bigger slugs might even be able to survive. Normally, it takes about six to ten days until the slugs die.
After three days, the slugs stop eating.

A nematode infestation can be recognized by the top of the slugs visibly swelling up.

slug population booms reasons
Slugs that live on the ground are not normally affected by nematodes.

Snails are not attacked. Spanish slugs are also insensitive to the parasite.

This is because ph-nematodes live underground, so do not usually come into contact with slugs and snails that live above ground.

This parasite is suitable for controlling the field slug (also known as garden slug), a species that also lives below the soil’s surface and is therefore easy prey for nematodes.

field slug nematodes
Field slugs live underground and are attacked by nematodes.

How to use nematodes

Normally, nematodes are applied with water on wet, open soil, not on lawns.

This is because they need moist soil to be able to move and to make their way into the ground.

Therefore, if the soil is not already wet, it must be watered before applying the nematodes.

To bring the nematodes out into the garden, you can use a watering can.

Follow the manufacturer’s instructions so that you obtain the correct ratio of nematodes to water.

Watering can garden nematodes
Spray nematodes with plenty of water.

Care must be taken to keep the soil moist in the weeks that follow, otherwise the nematodes will not be able to move and will slowly die.

After three to eight weeks, you can expect a decline in the slug population.

You should note that nematodes are very sensitive to light.

With direct UV radiation, they die quickly.

This is why they do not stay on the surface, but quickly crawl inside the soil.

The application should, therefore, take place in the evening or when the sky is overcast.

At temperatures below 50 degrees Fahrenheit (ca. 10 °C), the parasites become inactive.

At temperatures of 54 degrees Fahrenheit (ca. 12 °C) and higher, they begin to feel comfortable.

Temperatures should not rise above 77 degrees Fahrenheit (ca. 25 °C).

The application usually takes place between March and September and can be repeated after two months.

Video: Application of Nematodes

This gentleman never made a follow-up video to report on the success of the nematode application.

In his allotment diary, however, we learn that two weeks later he still had a slug problem.

And one month later, he started to put up electric slug fences.

Slug & Snail Fence | Protective Barrier

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Health Considerations and Risks 

Nematode-enriched water should not be sprayed onto edible plants.

While there is typically no danger to humans, individuals with weakened immune systems should not come into contact with nematodes.

After use, hands should be washed thoroughly.

Be sure to keep nematodes out of the reach of children and pets.

advantages strengths of this slug controlAdvantages

One advantage is that their efficacy against field slugs has been clearly demonstrated, and nematodes have been approved as being beneficial in organic farming.

In addition, it is advantageous that snails such as the protected Roman snail are not attacked by the parasites.

Disadvantages weaknesses of this slug controlDisadvantages

One disadvantage is that roundworms are highly sensitive.

They do not tolerate heat, cold, dryness, or light.

In addition, it takes a few weeks before the effects are seen.

Therefore, an acute infestation cannot be suppressed.

Another disadvantage is that the Spanish slug cannot be controlled with ph-nematodes.

Contrary to the information provided by the manufacturer, the use of twice the amount against Spanish slugs is reported to be unsuccessful.

In addition, it is not possible to settle nematodes in the garden, which is why there is no sustainable effect.

Regular use is therefore extremely cost-intensive.

Even if the parasites are supposedly harmless to humans, there is a residual health risk.

plus minusConclusion

For these reasons, I would consider the use of nematodes only in extreme circumstances; for example, when hundreds of field slugs threaten to destroy a whole crop.

Since nematodes need to be applied a couple of times during the garden season, this method becomes not only expensive but also time-consuming.

This remedy does not work against the Spanish slug, which is found in gardens across Europe. The use of nematodes in this case only leads to a lot more frustration.

There are many other, cheaper, alternative slug control measures that work in a more peaceful and sustainable way.

Raw sheep wool as protection against snails & slugs

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Products and Prices

Nematodes should be ordered or purchased at short notice, as they can only be stored in the refrigerator for a short while.

They can die quickly during transportation and store.

The information about the lifespan varies from one to three weeks.

The costs depend on the quantity and range from 0.30 to 0.60 $/£/€ per square meter.

At 1000 sq ft (ca. 100 m²) you are already around 30 to 60 $/£/€.

In a larger garden, the treatment can quickly cost hundreds of dollars/pounds/euros.

Hence, to use nematodes is far away from cheap.


Alternatives to Nematodes

Effective slug control should be a combination of different measures.

One part would be to attract natural enemies to your garden and to promote biodiversity

Further, you can set up snail and slug barriers and use natural attraction points to trap and collect the pests.

Another possibility is to plant mostly slug-resistant vegetables and herbs.

Slug Barriers

Peaceful Slug Control & Plant Protection

Snail & Slug Repellent Copper Tape | AdhesiveAnti-Slug Fence | Protective Barrier
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Sheep Wool Pellets | Natural Snail RepellentAnti-Slug Collars | For Single Plants | Multipack
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Mindful consumption: Please only buy what you or your garden really need.

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3 thoughts on “Nematodes for Slugs & Snails: Are They Really a Good Idea?”

  1. We were plagued by slugs, in the house, all over our very large garden. I used nematodes as described. Once, we have not seen any slugs since. I would thoroughly recommend this method of control. You don’t see them, they just get on with the job and presumably have been breeding since it was some years since I put them into the soil.Chris Cameron-Ramshaw ms

  2. “Even if the parasites are supposedly harmless to humans, there is a residual health risk.”

    Um… a little bit of clarification would have been appreciated for *that* statement. What *kind* of health risk? How *much* health risk? What would that health risk entail, and would there be a way to avoid it? These are, to me at least, rather important bits of information that were totally omitted.

  3. Monty Don tells us that crossing over previous snail trails inhibits breeding.Too crowded already…. Synthetic slime from the lab?Slow to show results but sure.


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