Nematodes – Nature’s Slug Control

Nematodes; the environmentally friendly method of slug control. A method used extensively by professional growers for years, but only recently made available to the general public.

These naturally occurring micro-organisms are already present in your garden soil, although in insufficient numbers to effectively control the average slug population unaided. Backup troops are needed, via the purchase of specially bred nematodes.

How nematodes work

Microscope image of several nematodes

Nematodes  (Phasmarhabditis hermaphrodita)

There are thousands of species of nematode, and some are parasites; meaning they infest and infect a host plant or animal, living off it in some way. Parasitic nematodes adapt to a specific host, and Phasmarhabditis hermaphrodita has evolved into a slug parasite.

Solely targeting slugs, these nematodes are perfectly harmless to children, pets, and other wildlife, and pose no hazard to food crops. In fact there are millions of them living quite happily in your garden right now.

Field Slug infected by nematodes

Infected Field Slug – note the swollen mantle

Dwelling in the soil, Phasmarhabditis hermaphrodita enters the slug while it’s below ground; infecting it with bacteria. The slug stops eating (your plants) within a few days, and dies within a week. The nematodes feed off the decomposing slug and reproduce, creating a new generation to move on and infect more slugs.

When slug numbers are sufficiently diminished, these nematodes die back to their natural levels once more.

Nematodes and snails

Slugs evolved from snails so the same nematodes are just as deadly to snails too. But in practice they’re not quite as effective because the snail is a surface dweller, hence there’s less chance of it coming into contact with the soil dwelling nematodes.

Wise precaution

Phasmarhabditis hermaphrodita will infect and kill water snails. Use carefully around ponds, allowing a safe margin of at least 15cm (6”).

Benefits of using nematodes

Much preferred to those horrid little blue pellets, nematodes have a lot going for them when it comes to environmentally friendly slug control. Benefits include:

  • Totally organic and environmentally friendly.
  • Completely harmless to children, pets, birds, and wildlife.
  • Perfectly safe to use around food crops.
  • The slug retreats underground before it dies, so you aren’t left with an abundance of dead slugs on the surface.
  • Dead slugs eaten by other creatures are non-toxic.
  • Impossible to over-apply.
  • Works well in wet weather; exactly the conditions where slugs are most active and destructive, and exactly the conditions that render poison pellets less effective.
  • Compatible with most garden chemicals – including fertilisers – although it’s best to apply them at different times.
  • You’re not introducing foreign entities into your garden; simply ‘topping up’ the good microbes that are already there.
  • You get the same benefits that commercial growers have been enjoying for over twenty years.

Nemaslug – nematode slug killer

Nemaslug pack

Nemaslug – Slug Killer

Nematodes are living organisms that need careful storage, which is why you don’t see them on the shelves at the garden centre. Instead, you need to order them direct from an approved supplier like Harrod Horticultural, who incidentally offer a good range of other garden products too.

Nemaslug is the brand you’ll find in the UK, and it’s available in two pack sizes:

  • Small Pack – Up to 40m² (50yd²)
  • Large Pack – Up to 100m² (125yd²)

The small Nemaslug pack contains around 12 million nematodes, the large around 30 million. Don’t ask me how they count them!

Nemaslug slug killer
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How to use your nematodes

  • If you aren’t ready to use your nematodes right away, leave them sealed in their packs and pop them in the refrigerator. They’re perfectly harmless...  honest! Keeping them below 5°C (40°F) keeps them inactive, but DO NOT freeze. Observe the ‘use by’ date, which is usually up to one month.
  • Nematodes are perishable so don’t be tempted to reseal once opened, or store the made up solution. Use the entire contents immediately.
  • The best time to apply is when the ground is moist, allowing the nematodes easy soil penetration. Water first if necessary. Evening is preferable because the soil doesn’t dry out as quickly. If the ground is compacted, dig it over first.
  • Simply mix with water and apply as per the product instructions. A coarse rose watering can is probably easiest, but for a large area a hosepipe feeder (see below) might be more convenient. This delivers an amazing 300,000 nematodes to each square metre of garden!
  • Water over the area once more afterwards to thoroughly wash the nematodes into the soil. Wash any off the plant leaves with more water; not because they pose a hazard but because they’ll perish. They can only survive in the soil.
  • During particularly dry spells, try to keep the ground damp.
  • The best time to apply is early in the growing season. This targets the young slugs before they wreak too much havoc; thus providing protection for your tender plants at their most vulnerable time.
  • Avoid periods when soil temperatures are below 5°C (40°F). Nematodes will survive a few frosts but, like the slug, are inactive during such conditions, making it a rather wasted effort.
  • Remember than unlike the instant results from products like pellets, this method requires a few weeks to reach full effectiveness.

Nematode hosepipe feeder

Miracle-Gro nematode hosepipe feeder

Nematode hosepipe feeder

While a watering can is probably easiest and most accurate for treating a small area, a hosepipe feeder is ideal for larger gardens.

Manufactured by Miracle-Gro, this feeder is the one recommended for the hosepipe application of nematode products.

  • Three spay patterns.
  • Uses standard Hozelock fitting (supplied).
  • Suitable for foliar sprays and soluble feeds too, but wash thoroughly between different applications.

Nematode hosepipe feeder
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Repeat applications

One nematode application should last for six to eight weeks. This maybe sufficient for the entire season because your plants are probably now hardy enough to withstand a little slug nibbling.

One exception is root crops like potatoes, which are a particular favourite of the Garden Slug and Keel Slug. To deal with this menace, a second later application can be used. Alternatively, if you don’t have any tender early plants to worry about, delay your first application until these subterranean crops are nearing maturity.

With this in mind, a handy ‘phased treatment programme’ is also available. Simply place your order for two or three packs and they’re automatically delivered at six-weekly intervals; no need for you to remember when the next application is due!

Watch this short video to see how easy it is to use your Nemaslug Slug Killer

What do you want to do now

Did you

A slug lays 20-100 eggs several times a year

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Organic Slug Killer

Nemaslug slug killer

The perfect choice for the ecological gardener who hates using chemicals and poisons in the garden.

Up to two months slug protection from a single application.

Harmless to birds, animals, and children. Safe to use on food crops. Dead slugs are non-toxic to other creatures.

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