control and prevention of grubs

Maggots are the larvae of beetles and under the lawn they can be a real pest for gardeners, especially if you like green even grass. Not only are they unsightly, but they can also cause serious damage to your lawn. The good news is that there are organic nematodes (nematodes) to control leatherjackets organically. On this page, we discuss how to recognise grubs, what beetle species they come from and, of course, how to control and prevent them with Heterorhabditis bacteriophora nematodes.

What do grubs look like?

Scarab larvae are white C-shaped beetle larvae (family of leaf beetles) that grow about half an inch to 4 cm long. These lawn larvae have a soft body with legs at the head. In June through September, they feed on the roots of the grass and organic material in the soil. This affects patches in the grass and other crops. The grubs eventually turn into adult beetles and emerge from the soil to then mate and lay eggs, which hatch into larvae. We speak of an infestation when there are more than 10 larvae per square metre.

When are they grubs?

Scarab grubs in the lawn that are larger than 3 centimetres are almost always grubs of the cockchafer or rhinoceros beetle. There is also the dung beetle, which is present between November and April and has a length of about 2 centimetres. Larvae smaller than 2 cm are usually from the June beetle or rose chafer.
The control of grubs today is done exclusively with biological control agents. This remedy is often popularly called aaltje called nematodes, but in the professional market they are referred to as nematodes. The period when these nematodes are effective is usually spring and autumn. At this time of year, the larvae of the beetles are smallest and therefore still best controlled with nematodes. Below is a brief overview of the various beetle species that cause leatherjackets and thus damage the grass:

The cockchafer


The cockchafer is officially called Melolontha Melolontha and is one of the best-known beetle species. They lay eggs in spring and autumn. These eggs eventually develop into cockchafer larvae, i.e. grubs, and feed on the roots of grass among other things. Because this is such a well-known beetle species and is often associated with grubs, we have written a complete page about it, which can be found on this page Chickadee .

The June beetle

June beetle

The June beetle is officially called Amphimallon solstitiale and, like the May beetle, is a well-known species in the Netherlands. They cause the same damage as the Meikever by laying eggs which later become grubs. They occur only as the name suggests, especially in the month of June. We have also written a separate page for this beetle species, June beetle .

The Colorado potato beetle

Colorado potato beetle

The Colorado potato beetle, officially: Leptinotarsa decemlineata is, as seen above, a beautiful sight. But, like the May and June beetle, it can also cause a lot of damage. The Colorado potato beetle particularly targets potatoes, aubergines and tomatoes. Warm summers are favourable for the Colorado potato beetle, when they can lay up to 3 generations of eggs, which later become grubs. More information can be found on this page: Colorado beetle.

The Rose Chafer / Stag beetle

Rose Chafer

The Rose Beetle/Johanneskever, with the official name Phyllopertha horticola is also a beautiful insect, but unfortunately this beetle species can also cause a lot of damage and this is again due to the grubs. And controlling the Rose Beetle should actually be done preventively because the first two larval stages cause hardly any damage. In the third stage, that changes abruptly and damage to the grass occurs quickly. Read more on the page about the Rose chafer/Johanneskever.

The yew beetle

Vine weevil

Officially called the Yew Beetle: Otiorhynchus Sulcatus and is from the weevil family. It can be recognised by its long snout and feelers. This beetle species cannot fly, the shield you see above is fully grown with its body. The vine weevil also goes through four stages: egg, larvae (grubs), pupal stage and eventually they become an adult beetle. You can find more information on this page: Vine weevil.

Controlling grubs

Of course, the most important question is: how do I control grubs in the garden? Below is also a section on preventing unwanted beetle species and thus its eggs and larva. But now first further on control. Firstly, fortunately, nowadays only biological control is allowed. And the most effective method is by doing so with nematodes, incidentally professionals usually call them nematodes. Nematodes are not visible to the naked eye, but are extremely effective against grubs. We have also written a separate page on this subject: Nematodes and nematodes

Briefly, the nematodes enter their host, in this case grubs, and release bacteria that kill the larvae. When no grubs are present, the nematodes die and leave no trace. In doing so, they are not harmful to humans or animals. The nematodes you need are described below.

Heterorhabditis bacteriophora nematodes against grubs

Heterorhabditis bacteriophora nematodes can be used as biological control of grubs. They parasitise the larvae of the previously mentioned beetle species (May beetle, June beetle, Colorado beetle, Rose chafer, and the Yew beetle). They do this by releasing bacteria into the host, in this case the larva of the beetle in question.

Best time to control grubs

Unfortunately, you cannot control grubs all year round. This is partly due to the temperature, but also to the period when beetles lay eggs. When the larvae are too large, it becomes more difficult for nematodes to control them. The period in which beetles lay their eggs is different but close together. So if you are not sure which beetle species lays the eggs, you can use the guidelines below.


  • From mid-April to the end of September
  • Soil temperature should be above 12°C
  • Control after 6 to 8 weeks after the flight
  • Control twice a year, spring and autumn.

Scarab prevention is better than cure

Biodiversity helps prevent grubs. You do this by planting different vegetation in your garden. If your garden consists only of a lawn, grubs can develop at lightning speed and are a persistent pest that will completely ruin your lawn. A healthy lawn is also important. By healthy we mean thick and evenly distributed grass. Beetles of the previously mentioned species, prefer thin and short cut grass. Therefore, we recommend cutting the grass no shorter than five centimetres. The leatherjackets nibble on roots of the grass at all stages. As they get closer to pupation, they will start eating more and more roots. Due to this fact, to prevent grubs, you should invest in your lawn and soil. For instance, you can do this when sowing or using organic fertiliser.

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