Some grubs can do massive damage and destroy entire lawns. How to deal effectively with the beetle larvae.
The larvae of many beetle species are called grubs. Especially the larvae of the cockchafer (Melolontha), the June beetle (Amphimallon solstitiale) and the garden beetle (Phyllopertha horticola). ). All three belong to the scarab beetle family (Scarabaeidae) and can cause a lot of damage to your lawn. However, there are also beneficial insects among the grubs, some of which are even protected. We'll tell you how to identify the malware and how to counteract it.
Distinguish grubs: Characteristics of harmful grubs
It is important that you correctly identify the harmful grubs first. Each species has distinctive features that you can quickly identify with the necessary prior knowledge. We'll tell you how to correctly identify the unpopular guests in your garden and distinguish them from beneficial ones.
The grub of the cockchafer becomes up to four centimeters long. Its expected lifespan is between three and four years. The cockchafer grub has a relatively even shape over the entire body and is slightly yellow in colour. Depending on the stage of development, this color can darken somewhat (towards brownish). The cockchafer grub is characterized by strong mandibles (mouth parts) and pairs of legs on the front body.
The grubs of the June Beetle look very similar to those of the May Beetle, but are a bit smaller. They are usually indistinguishable from laypeople. The so-called locomotion test should also help the untrained eye to distinguish the grubs of the two species. If you lay the larvae on their backs on a smooth surface (e.g. a pavement slab), you should be able to tell which grubs they are by the way they move. The cockchafer grub should curl up lying on its side. June beetle larvae, on the other hand, should stretch and then try to crawl.
The grubs of the garden beetle are not so uniformshaped like those of the May and June beetle. While they are rather narrow on the front body, the abdomen thickens with increasing length. The garden chafer grubs are bright white in color, but sometimes have greyish shades. Their mouthparts and legs appear rather small, but they are all the more powerful. During the "locomotion test", the garden chafer's grub catches the eye with its caterpillar-like movements.
Warning: Be sure to identify your grubs before taking any action. The animals can also be the larva of the rhinoceros beetle (Oryctes nasicornis), for example. This is a beneficial insect and is under protection. You can find out how to recognize useful grubs and distinguish them from harmful ones in our article on grubs.
Gugs in the lawn: Symptoms of damage
You can tell that your own lawn is infested with grubs when the grass plants seem to be dying off over a large area. Note: The dying of the lawn can of course also have other causes, which is why you should substantiate this assumption again. Simply dig up a small portion of the dead area and search the excavation for larvae.
The grubs move a few centimeters underground and feed on rotting but also fresh plant material. It can happen that whole turfs are eaten up by a large number of infestations. What remains is a brown and dried up meadow.
Insider tip: The female grubs prefer to fly to short-mowed lawns to lay their eggs. So if the females appear in large numbers during the "cockchafer years", you should rather stop mowing the lawn for about three weeks.
Successfully fighting grubs in the lawn
The best way to prevent grubs is to encourage their enemies in your own garden. A homely, "untidy" corner in the garden attracts hedgehogs and birds, which willingly take care of the grub plague. And the mole also likes to eat grubs. A more inconspicuous antagonist is the insect infesting fungus Beauveria brongniartii. It occurs in most soils and affects the grubs there. It grows through them with its mushroom mycelium and kills them in the process. Unfortunately, Beauveria brongniartii cannot be specifically settled by private users, but is favored by moist soil. At the same time, grubs prefer rather dry locations.In the long term, it therefore makes sense to improve dry sandy soils by building up humus so that they also store moisture in summer.
Fighting grubs with nets
Observe a strong flight of May beetles in a "May beetle year", then you can cover your lawn with close-meshed nets or tarpaulins. The flight time of the beetles lasts about three weeks. Meanwhile, you should prevent the female beetles from laying their eggs in your lawn. Of course, covering the lawn is only an option for smaller areas. If you use tarps, it is also necessary to uncover the area for a few hours a day so that the lawn does not die from lack of light.
Fighting grubs with nematodes
In the case of an acute infestation, however, the above methods do not really help. The most effective way to combat grubs is with nematodes. Nematodes are tiny beneficial insects that parasitize and kill beetle larvae. However, the little helpers can only be used effectively in young larval stages, which is why the correct time of application should be observed. Control with nematodes between July and September is ideal.
You also have to make sure that you choose the right nematode species so that a beneficial-host interaction can take place. For example, our Plantura HB nematodes of the species Heterorhabditis bacteriophora work reliably against grubs in lawns. To use the beneficial insects, the temperatures should be permanently above 12 °C and it should not be too dry or extremely wet. The nematodes come in powder form and are dissolved in water and spread over the lawn using a watering can.
Remove Grubling Damage
You have discovered a population of grubs in your garden and successfully fought them, or have the beetles finally hatched from the pupation and flown? What remains is damage to the lawn, which can now all too easily be colonized by weeds. If there are only small holes in the area, a fast-germinating lawn patch is ideal - the slower weeds don't stand a chance. If your entire lawn is affected, only a new lawn seed with the right lawn seed mixture will help. We will be happy to help you choose the right type of lawn.
Conclusion: Fortunately, a heavy infestation with grubs rarely occurs in lawns. Beneficial insects can be promoted in the garden as a preventive measure. Also favors aDamp, humus-rich soil encourages the colonization of opponents such as the insect-infesting fungus Beauveria brongniartii and at the same time makes the location unattractive for beetles to lay their eggs.
If you want to learn more about nematodes as beneficial insects, read on here.