A Comprehensive Guide to Understanding Nematodes

John Plant
Oct 3
5 min read

Hostas are pretty well a foolproof perennial, with the exception of one or two problems. The two biggest will be the slugs & snails, and Vine Weevil.

Nematodes are one of the many accepted methods of reducing the incident of slugs and vine weevil amongst Hostas.

We use nematode control for both Vine Weevil and slugs & snails.

As nematodes are not available in garden centres, and need to be bought on-line, they are not generally that well known. Let’s put that to rest now!

How does it work? How much do I need? When should I apply. All these questions will be answered as we go through the blog. Some of the information may be a little technical!

What are nematodes?

Nematodes are one of the most common animals on earth. There are over 20,000 different species of nematodes. They look like microscopic worms, but technically they are not worms. They are so small that they can’t be seen easily with the naked eye.

There are 20,000 species of Nematode living in different environments such as soil, or water. Some eat bacteria, fungi or plants, and some are parasites of insects. These are what we want to kill vine weevil - Steinernema Kraussei. For killing slugs - Phasmarhabditis hermaphrodita. Best well known brand being Nemaslug/ Nemasys manifactured by BASF

Different species of nematode are used to control different insects, so ensure you get the right one. Most types will only attack one type of insect, make sure this is one for killing vine weevils or slugs.

How do they work?

The microscopic worm will travel through moist soil or compost and kill the larvae of the slug or vine weevil, burrow into them and kill them. Not a nice way to go, but you won’t see this. They also prevent adults eggs from hatching.

Apply nematodes when the larvae are present, & soil temperature is at least 12c, for a few hours a day. (April to October). It will take a couple of weeks to start working, but it is all in the soil, so you won’t be able to see.

N.B You have only a short while just now to apply your nematodes. By early November it will be getting too cold.

How are nematodes bred?

The nematodes are then reared in state of the art, liquid fermentation facilities before being formulated into a product which is able to keep the nematode in an alive but dormant state so that it reaches the grower in the best condition.

BASF is the world’s largest breeder of beneficial nematodes for use in UK domestic garden and worldwide agricultural crop protection products and the Littlehampton facility is the only one of its kind in the UK. Each year the company grows trillions of beneficial nematodes for this programme.

The factory is known at ‘Nematode Heaven’ as everything they need to breed, live and have a healthy life-style is found for them. The basis of the BASF operation is that they are recreating the natural environment to enable nematodes to live and multiply in large volumes to enable us to harvest them for pest control use

how nematodes work screenshot — Screenshot from BASF website.

Are nematodes harmful to humans or animals?

The simple answer is no! They are of no danger to humans or animals.

A few species out of the 20,000, such as pinworm, are harmful to humans or pets, such as cats & dogs, but these are very rare. Most species play a very important role in nutrient cycling and release of nutrients for plant growth.

The nematodes in a biological control product are beneficial, meaning they only kill insects, and not even all insects; they will only be parasites of specific pests. They have no effect on humans, as they cannot interact with humans at all.

The benefits of using Nematodes.

They are natural. No chemicals. They are safe for, adults, children & pets. No gloves required. Nematodes are natural parasites and can move through the soil to hunt them down.

Only kills the intended pest, and pests do not become resistant over time. Works on any plant with no restrictions on flowering plants.

Easy to use. Just follow instructions, mixing with water and apply.

Very effective!

Kills at the larvae stage which cause most damage.

Nematodes will do all the work by themselves. Apply & forget.

Effective over a 2 week period until all larvae are dead.

Are the any disadvantages?

Your Nematodes cannot be purchase at a garden centre, and will have to be purchased on line. They will arrive by post and must be refrigerated before use. The supplier will keep in a chilled warehouse and prompt delivery is to ensure they don’t die in transit. Delivery is generally free, but with a no return policy, afterall they are live.

Many gardeners are probably not aware of Nematodes any some carry on with using chemical controls instead.

Soil needs to be moist, both when applied and for 2 weeks after. The nematodes move through the moist soil like worms. As natural parasites of vine weevil larvae and slugs, they hunt them down and burrow inside. They reproduce inside the host, killing it. More nematodes emerge from the host and seek out more vine weevil & slugs until all are dead. Once all they are all dead, the nematodes have nothing to reproduce inside of and also die out.

How to apply?

Mix the powder (looks a bit like live yeast) either in a watering can or prescribed hosepipe dispenser. Apply as directed.

Store the package in the fridge, checking the use by date, but do not freeze.

Keep the soil moist for 2 weeks after application.

Use the whole pack at the same time. Do not store partly used packs or even made-up solutions.

How many nematodes will I need?

From the manufacturer website you can calculate what you will need. A 10 square metre will treat 10sq m of soil or 175 pots. Did you know that there are over 20,000 nematodes in each 10sq m pack.

When is the best time to apply Nematodes for vine weevil?

Vine weevil larvae and slugs are most active in late spring and early autumn, which probably means making two applications. High infestations may also require two applications about 1 month apart.

Nematodes for Vine Weevil will not work on slugs and vice-versa. Specific nematodes are required for each type of treatment, but work in exactly the same way.

Vine Weevil in particular, is a persistent critter, but for the last 2 years we have used Nematodes and found the incidence, discovery of Vine Weevil grubs virtually nil, and pretty-well no signs of the leaf eating adults. This is the same with slugs & snails. Very happy with this.

We discovered nematodes three years ago, and we're pleased to have found them. We regularly use both types, and they significantly helped with the of pests.

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