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How to fight against white grubs?

How to fight against white grubs?

What is the white worm?

The white worm is here chafer larva (Melolontha melolontha), a beetle insect from the beetle family. In May, once adult and out of the ground, the chafer is easily recognized by its noisy flight, at dusk.

A few decades ago, the chafer and its white worm were a real plague for a large number of cultures. Today, their population and their nuisance power have greatly decreased, in particular due to the intensification of agricultural practices and undoubtedly the excessive use of pesticides.
 

What does the white worm look like?

The chafer's larva can be recognized by its arched shape, its white-yellowish body which includes a black posterior end, its well marked red head and its fairly long legs. Once grown, it measures 20 to 30 millimeters, and looks like a beetle blackish, with brown elytra.

The evolutionary cycle of the chafer spans three years:

1. The adult emerges from the ground in May. The female begins to lay a month later, about twenty centimeters deep, in loose, warm soil. The hatching and the first moult take place during the summer. From the first cold, the larvae hibernate in the ground.
2. In the following spring, the larvae, 4 cm long, rise to the surface to feed on the roots. It is at this stage that the white worm is the most voracious, and represents the greatest danger.
3. A year later, the white worm still causes some damage, but pupates during the summer and waits until the following spring to transform into an adult. The chafer is then ready to emerge from the ground and fly away. For the same region, the thefts of this insect only occur every three years.

Damage related to white grubs

The white chafer worm particularly likes vegetable plants with tubers or fleshy roots. It also attacks the roots of shrubs or perennials. In the event of a chafer larva attack, the subject:

  • First presents a slowdown or even a stop in growth.
  • Then the plant turns yellow and withers away.
  • Sees its roots and its collar bitten and gnawed, or even severed, in the case of young plants.

White grubs are visible near the roots. The consequences can result in the total destruction of young cultures.
 

White worm victims

A large number of plants can be attacked by white beetles. In the vegetable patch, we can mention:

  • Beet,
  • Potato,
  • The carrot,
  • Turnip,
  • Strawberry plant,
  • And in field crops: corn and sunflower.

Distinguish between the white chafer worm and that of the golden ketonia

The larvae of the chafer and the golden ketonia are similar and should not be confused. The larvae of ketones are particularly useful in the garden, since they feed on plant waste and are beneficial to the transformation of compost; it would therefore be a shame to eradicate them by taking them for pests!

Visually, the larvae of the golden cetony are a little smaller, whiter, with short legs and a head not very visible, reduced compared to the body. They also have a much greater mobility than those of the chafer.

How to fight against the white worm?

The white chafer worm only requires large-scale treatments in exceptional cases. In spring, during the first work of the earth, the identified larvae can be taken, and offered for tasting on a plate to birds and hedgehogs, natural predators who will make a feast of it. It is advisable to tolerate moles which also participate in their elimination. It will also be good to hoe the soil regularly.

If the chafer larva is a real problem for crops, it is possible to get rid of it biologically by watering the soil with entomophagous nematodes (sold in garden centers), or by sowing the soil with spores of Beauveria brongniartii, a fungus whose toxins kill the larvae.