As of: March 28, 2024, 2:30 p.m
By: Ines Alms
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If you want to get rid of grubs in the garden using their natural enemies, you can use nematodes. But these are not equally suitable for every type of beetle.
Grubs, the large larvae of May, June or, for example, garden leaf beetles, seem to particularly like to sit where hobby gardeners don't want them: in raised beds or in the lawn they nibble on vegetables and flowers and endanger the harvest. Finding, disposing of or even killing the animals is not for everyone, but there are natural enemies that remove the beetle larvae in an environmentally friendly way. Nematodes, tiny roundworms, are promising here, but you have to know the differences and know how to use the beneficial insects correctly.
Important distinction: Which species of grubs do you want to control with nematodes?
For example, in lawns, grubs can cause great damage by eating away at grass roots. © Zoonar/Imago
The nematodes, which are approximately half a millimeter in size, are harmless to humans and other animals. As parasites, the beneficial insects can search for grubs in the soil, colonize the larvae and reproduce in them. This kills the grubs and the nematodes move on to their next host until they can no longer find food.
There are over 20,000 species of nematodes, some of which are also pests that can attack plants, especially roots. Others make themselves useful by fighting the dreaded black weevil or snails. Therefore, when used against grubs, you have to use certain species that specialize in this target group.
You can find even more exciting garden topics in the regular newsletter from our partner 24garten.de.
Particularly important: First you have to know which beetle larvae colonize the garden. Are they really pests or even beneficial insects, such as the rare rhinoceros beetle? Grubs are also generally desirable in the compost, as they carry out important tasks and convert the garden waste into humus. First of all, you should identify the grubs: larvae of the garden chafer beetle, June beetle and May beetle can be controlled with the nematodes. If the larvae are larger than one and a half or two centimeters, the use of nematodes is usually no longer very effective and you have to increase the dose or resort to other methods.
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Use nematodes correctly against grubs
There are also the following to note when using it:
Obtain nematodes of this type from specialist retailers or online
Heterorhabditis bacteriophora (HB or HM nematodes), which attack the larvae of garden leaf beetles and June beetles. The genus Steinernema can also be used in combination against cockchafer grubs.
It's the quantity that counts: you need around half a million nematodes per square meter, which are released live in clay granules - please note the product information here.
Nematodes only become active at soil temperatures above 12 to 14 degrees Celsius, so you should wait for these temperatures in spring. April to September is a good time for this, as that is when the larvae hatch.
The application is simple: the granules are dissolved in water, stirred regularly and the bed or lawn is watered with it. In the next three weeks you have to keep the soil evenly moist and not allow it to dry out.
Most infected grubs die within two weeks. In order to permanently get rid of the grubs, it is sometimes necessary to use them for two to three years.
Please note: Grubs are a natural product and usually only last about a week in the refrigerator after receipt. It doesn't make sense to buy the roundworms in stock.