If you discover grubs in your garden while digging, you don’t have to panic right away. Not all of these larvae are really harmful. Rather, there are good ones and bad ones. Even the rather harmful white caterpillars in the soil usually do not cause too much damage. However, it becomes critical when there is a mass infestation of cockchafer beetles. Then there is the highest danger. In most cases, the only solution is to plow up the entire area. But this is a rare exception.
Good and bad grubs
These are white larvae that emerge from eggs laid in the soil by certain species of beetles. The caterpillar-like creatures remain in the soil for up to four years and can grow up to six centimeters long. Their body is distinctly fleshy. On its front part there are chewing tools, the rear part is conspicuously thickened. Their basic white color can vary through light gray and orange-brown to black. They feed on humus in the early stages, but some species later switch to the tender roots of grasses and shrubs. In the case of a very heavy infestation of grubs, this can lead to the death of the affected plants. However, a basic distinction must be made between beneficial insects and pests.
The following are considered pests:
- May beetle
- June beetle
- Garden leaf beetle
Beneficial insects include mainly:
- Rhinoceros beetle
- Rose beetle
- common rose beetle, Cetonia aurata
The latter may even be quite specially protected under the Federal Nature Conservation Act. They may not be caught, injured or even killed. Since they only eat dead plant material, they do not pose the slightest danger to the garden. On the contrary, they make a decisive contribution to the natural formation of humus in the soil.
It is not so easy to recognize which type of plantain it is. For one thing, they rarely leave the soil, instead remaining hidden deep in the ground. For another, a larva freed from the soil would have to be examined very closely. A clear indication of a possible larval infestation is when entire sections of grass or other plant areas die. Then you should definitely take a spade and look at what is happening in the soil. Most often you will encounter the larvae of the cockchafer. These can be identified relatively clearly by their mode of locomotion – they move sinuously in the lateral position.
Note: Dead plants are a sign that there are bad grubs in the soil. Good ones, on the other hand, do not cause damage to plants in the first place.
In most cases, the infestation is very low. Damage does occur occasionally, but it is usually very limited. However, it can happen, especially with cockchafer, that thousands of grubs are in the soil. This usually depends on the region and the weather conditions in spring. Such an extreme infestation for inevitably leads to a clear cut and to very large damages. However, it usually does not occur every year.
There are a number of preventive measures that provide relatively reliable protection against an infestation of woodlice. However, both bad and good larvae are affected. The goal is always to prevent the beetles from laying their eggs in the soil in the first place. The following measures help:
Do not light the garden at night, as beetles are attracted to light.
In May and June, lay insect protection nets over beds and compost.
Regularly scarify or loosen the lawn.
Maintain the property properly and especially remove weeds and dead wood.
A very reliable protection is also a root protection grid worked into the soil. However, this measure requires an immense amount of work and is therefore only considered in the rarest of cases.
- Rose beetle grubs
- Rose chafer grubs
The concrete control of the grubs in the soil usually has to be done manually. This usually means digging up a partial area of dead plants and collecting the grubs that come to light by hand. The larvae should then be placed in the trash can for disposal. It is not advisable to release them in another place. Certain plant species are also very helpful in controlling them. Delphiniums and geraniums in the garden contain substances that are toxic to the larvae. Garlic, in turn, drives away the animals.
Finally, it is also possible to kill them with nematodes, i.e. threadworms. Nematodes are now available in specialized stores. One package of the small worms is sufficient on average for a lawn area of around 20 square meters. The worms infest the larvae and thus ensure their death in a completely natural way.
Tip: If you design your garden in such a way that hedgehogs, mice and birds feel at home there, you have very effective partners at your side to combat white caterpillars in the soil. For these animals they are a delicacy, which they specifically search for in the soil.