Once you have pests like the vine weevil in your garden, it is often difficult to get rid of them. A simple, biological way of controlling the black weevil is nematodes.
It is often difficult to get the vine weevil out of your garden [Photo: Jiri Prochazka / Shutterstock.com]
This article provides simple hints and tips for using nematodes against black weevils. Especially at night, they do their mischief and leave characteristic traces of feeding on plants such as rhododendrons, roses, clematis or strawberries. However, the larvae of the beetle, which damage plant roots, are more problematic than the unsightly feeding marks.
Recognize black weevil infestation
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If a garden is afflicted by black weevils, this can usually be recognized relatively easily by means of the semicircular feeding places, the so-called bay feeding, on the leaves of ornamental plants such as rhododendrons. The real problem for the plants is not the nocturnal beetle, but its larva. The larvae live in the ground, eat the roots of the plants there and often even peel off the bark on the root neck. The plant is thus cut off from its supply of water and nutrients and can die. Therefore, one should start fighting the black weevil quickly after discovery.
The vine weevil leaves characteristic traces of feeding: the bay feed [Photo: SusaZoom / Shutterstock.com]
Nematodes against black weevils: timing
During the year there are two phases in which the control of black weevils with nematodes is recommended: in spring from April to May or in late summer between August and September. The condition is that the floor temperature is above 12 ° C for a few hours a day. These recommendations result from the life cycle of the beetle and the temperature requirements of the nematodes. To achieve complete control, it makes sense to treat once in spring and once in late summer. Suitable nematodes are only effective against black weevil larvae and pupae, but not against the beetles or eggs of the black weevil. During the early treatment, the pupae and then the newly hatched larvae are killed in autumn. After application, the first larvae of the black weevil die within 7 days. Since the nematodes continue to multiply in the insects, the success of the control increases over time, so that a suitable long-term effect is achieved depending on the intensity of the infestation.
HB nematodes act against the larvae of the vine weevil [Photo: Tomasz Klejdysz / Shutterstock.com]
Which nematodes can be used against black weevils?
An example of nematodes that act against both the pupae and the larvae of the black weevil are our Plantura HB nematodes against black weevils and white grubs. HB nematodes are tiny roundworms of the species Heterorhabditis bacteriophora , approximately 0.6 mm in size. They look for larvae and pupae of the pests in the soil and invade them. There the nematodes continue to multiply and kill the infected larvae or pupae. Eventually the nematodes leave their host and infest other larvae.
Tip : In addition to fighting black weevils, HB nematodes can also help fight white grubs, which cause lawn damage.
Since HB nematodes only specialize in a few pests, they do not pose a threat to warm-blooded animals, humans or plants. You do not have to worry about the nematodes spreading unintentionally in your garden. As soon as the work of the nematodes is done, i.e. there are no more pupae or larvae of the black weevil in your garden, the number of nematodes continues to decrease. HB nematodes can also develop longer-lasting forms of persistence, so that a certain long-term protection remains.
Nematodes can also be used on food plants without hesitation [Photo: Jurga Jot / Shutterstock.com]
Note: There are other nematodes that are suitable for combating black weevils. Nematodes of the Steinernema kraussei species parasitize mainly larvae, whereas Steinernema carpocapsae attack the adult beetles. However, HB nematodes are the most commonly used because of their effectiveness.
Spread nematodes against black weevils
The application of our HB nematodes against black weevils and white grubs is easy and does not require any special equipment. However, a few points should be noted: Because nematodes are sensitive to UV light, they should only be applied in the morning or evening and when the sky is overcast. The required soil temperature of 12 ° C is important for effective reproduction of the nematodes and thus for successful application.
When storing nematode preparations, it should be noted that they are living organisms. Apply the beneficial insects as soon as possible after receipt. When stored in the refrigerator, nematodes can be kept for a maximum of 6 weeks.
Application instructions for nematodes against black weevils:
- Moisten dry soil.
- Stir the contents of the pack into 10 liters of water.
- Dilute the mixture further according to the number purchased and the area to be treated, as indicated in the application recommendation. If necessary, divide it into several watering cans or mix in several steps one after the other.
- Keep stirring the mixture vigorously, otherwise the nematodes will settle on the bottom.
- Pour the finished mixture into a watering device or a nematode sprayer and distribute evenly.
- Immediately after application, rinse with at least 1 liter of water per square meter to flush nematodes from plants into the soil if necessary.
- Do not allow the treated soil to dry out for at least the following 4 weeks, as the nematodes need moist soil to survive.
Note: The information provided primarily relates to our Plantura HB nematodes against black weevils. For other products there may be different instructions for use.
If you are not only struggling with the black weevil in your garden, you can read more about nematodes as beneficial insects in our special article.