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Recognize & successfully control weevils

Weevils can do a lot of damage to plants. We show you how you can recognize the unpleasant pest and fight it successfully.

The beetles with the typical shaped head can do a lot of damage in the garden. The beetles of the family of Curculionidae can be a few millimeters up to two centimeters in size. Here you can find out what you need to know about these guests in your garden and what is best to do against them.

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Weevils: The Life Cycle

The life cycle of around 800 species of weevils in Germany is quite similar. The crepuscular and nocturnal beetles have a trunk-like head that is pulled forward and at the tip of which the chewing mouthparts are located. The adult beetles have a dark colored, hard chitin shell. The beetle and its larvae feed on plants alone, often in a narrow circle of host plants. This means that the weevils do not eat their way across the vegetable garden, but are real gourmets. Depending on the species, they usually only prefer certain plants or plant families.

Some species of weevil reproduce parthenogenetically (unisexually). Therefore, the beetles in our latitudes are mostly females who lay unfertilized eggs in piles in the ground or in plant material, from which female weevils hatch again. Up to 1,000 eggs can be laid per female.

The optimal floor temperature is 16 to 27 ° C. The higher the soil moisture, the more beetles hatch. The larvae are legless, white and often have a dark head. They have a curved, maggot-shaped shape and have biting-chewing mouthparts. The larvae mine in plants or feed on the roots. Mining means that the larvae, so to speak, eat a mine or a tunnel into the plants. The tissue then dies around the ducts and turns brown.

The larval development depends on the temperature. In autumn the larvae reduce their feeding activity. Some species hibernate on the ground under dry leaves, others in the ground and there are also species that look for hiding places on trees under the bark to overwinter. The ripening process begins in May and lasts between 4 and 9 weeks. It is also important to mention the behavior of the beetles. Because as soon as the weevils perceive vibrations, they drop to the ground.

Weevils in the garden: the most feared species

There are a total of 50,000 species of weevils. That’s what the family does Curculionidae, to which even the feared bark beetles, which are feared in forestry, recently belong to the most species-rich beetle family. At the moment the Rübenderbrüssler (Bothynoderes punctiventris) Headlines because it is severely clogging sugar beet in Austria and is causing major problems for agriculture. The following species can be particularly problematic in your garden or on your fruit trees. Weevil plagues often affect rhododendrons in particular.

Dreaded species of weevil in the garden

  • Furrowed vine weevil (Otiorhynchus sulcatus)
    • Likes to eat strawberries, raspberries, blackberries, currants, rhododendrons, roses, cyclamen and grapevines.
  • Small or spotted cabbage weevil (Ceutorhynchus pallidactylus)
    • Likes to eat cabbage vegetables (cruciferous vegetables), radishes, horseradish and rapeseed.
  • Greater cabbage weevil or rape stem weevil (Ceutorhynchus napi)
    • Likes to eat cabbage, radishes, horseradish and rapeseed.
  • Cabbage weevil (Ceutorhynchus assimilis)
    • Likes to eat cabbage pods.
  • Striped scarab beetle (Sitona lineatus)
    • Likes to eat peas, beans and clover.
  • Cabbage weevil (Ceutorhynchus pleurostigma)
    • Likes to eat cabbage, radishes, horseradish and rapeseed.

Dreaded species of weevil in the orchard

  • Apple blossom cutter (Anthonomus pomorum)
    • Occurs on apple trees.
  • Narrow-bellied or green weevil (Phyllobius spp.)
    • Occur on willows, roses, apricot trees, and plum trees.
  • Pear bud picker (Anthonomus pyri)
    • Perform on pear trees.
  • Strawberry Blossom Piercer (Anthonomus rubi)
    • Occurs on strawberries, raspberries, and blackberries.

Portrait of the black weevil

The furrowed vine weevil (Otiorhynchus sulcatus) is one of the most economically important pests. The adult beetle likes to eat the buds of evergreens and deciduous trees such as rhododendrons or roses. The larvae tamper with the roots. This species also occurs on many different cultivated plants, from strawberries to our ornamental plants / shrubs to grapevines. This is why this beetle is also called Black Vine Weevil in English.

The weevil is around 8 to 13 mm in size and has an oval, elongated body shape. It is dark gray to black in color, but there are yellow scale hairs on its elytra, so it looks irregularly spotted. The flightless beetle eats bays in the leaves from the edge of the leaf. As soon as they hatch, the larvae feed on the root hairs, later also on the root neck and can even debark the base of the trunk of trees. The larvae also penetrate tubers and eat them up completely. This underground feeding activity can cause your plants to wither and die.

The apple blossom cutter in portrait

If you have a garden near the forest and you can find some apple or pear trees there, you could have problems with the little weevil (Anthonomus pomorum) to get. A cold spring is good for this 4 mm large beetle. It is light gray and has a light horizontal stripe on the wing covers. The apple blossom stick overwinters hidden on the trees or in the ground and begins to ripen in March. The beetles drill into the swelling buds and eat the sap that emerges. After mating, the females continue to feed on the closed flower buds and lay their eggs in them. The larva hatches after a few days and eats inside the flower. The damage caused by the apple blossom picker can be recognized by the fact that the eaten blossoms do not open, dry up and discolour.

Preventing weevil infestation: repelling instead of fighting

You can protect your plants, bushes and trees from weevils as a preventative measure. Especially if you have already had problems with the voracious beetles (for example in the previous year), these tips can prevent harm.

Since most weevils are active at night or at dusk, the weevils look for dark places during the day to hide and sleep. Shrewd gardeners can take advantage of this behavior and lay wide wooden boards around endangered plants. The weevils then gather under these boards. During the day you can then remove the boards and collect and dispose of the weevils sleeping underneath. Of course you won't catch all of the bugs this way, but you can reduce the infestation pressure.

Extra tip: Another method of catching the weevils is to make homemade traps, which you can hang in trees and shrubs, but can also be used indoors. These traps are basically similar to an insect hotel. To do this, take a flower pot, attach a string to the floor to hang it up and fill it with wood wool, straw or something similar. You hang this trap in the garden and the beetles will use it as a hiding place. Then all you have to do is wait a bit, check the traps regularly and remove the voracious weevils. But be careful not to kill any beneficial insects that may also be in your trap.

Another preventive measure can be to keep the soil moist. The female weevils prefer loose and dry soil for laying eggs. Regular and sufficient watering can therefore help. You can also disturb the larvae in the soil by chopping and loosening them more frequently. Encouraging the weevil's natural predators can also help in prevention. These include, in particular, birds, shrews and the hedgehog.

Fighting weevils: biological and chemical options

When weevils have spread to your garden and are causing damage, it's time to do something about the uninvited guests. You can find out what methods of combating it there are here.

Fight weevils biologically

There are a number of effective biological methods that can be used to attack weevils. The use of nematodes has proven particularly useful. These parasitize the weevil larvae in the soil and kill them. To treat the larvae in the soil, there are nematodes for watering. But there are also new products that capture the adult beetles. Similar to the wooden catching boards, special boards are laid out here, which are prepared with a nematode gel. Here you will find information on the correct use of nematodes as beneficial insects.

Another method is mechanical collection. The best way to do this is to hunt at night, as the weevils are out at dusk or at night. To do this, arm yourself with a flashlight and a bucket and collect the weevils. But what do you do with a bucket full of bugs? A tried and tested method is hot water. Heat some water and then pour it into the bucket. This is how you can kill the beetle.

An organic crop protection product is also suitable for combating weevils. The active ingredient is azadirachtin, better known as neem or neem. This natural pesticide is obtained from the seeds of the neem tree, has an inhibiting effect on the development of eggs and larvae and can therefore be used against the larvae. You can pour the remedy for this. In addition, when sprayed, the agent also shows action against the adult beetles.

Here we have summarized all biological control methods against weevils for you:

  • Nematodes
    • Nematodes for watering
    • Nematode gel on catch boards
  • Collecting the weevils
  • Azadirachtin or better known as neem

Chemical control of weevils with insecticides

If you resort to chemical weevil control, you should not use nematodes at the same time. It is possible that the insecticides also have an effect on the nematodes. The following active ingredients are approved for household use:

  • Thiacloprid Spinosyne A and D
  • Deltamethrin acetamiprid

Before using any insecticide, always read and follow the instructions for use. Personal protection and dosage are particularly important. If you use too little insecticides or other pesticides, resistance can develop and none of us want a resistant weevil in their home garden.

We recommend the following products for combating:
  • HM nematodes: beneficial insects to control the black weevil and garden beetle.
  • Neudorff beneficial insects order set: Tick the desired beneficial insect on the order form, send it in and receive it conveniently by post.
  • Neudorff Neem Plus Pest-Free: A purely plant-based spray (neem meal + rapeseed oil), which can be used against other pests (weevils, aphids, etc.) in addition to the boxwood moth.

Weevils in the apartment: control and prevent

When you get new ornamental plants, you should always repot them in fresh soil and not use cheap soil. Insect larvae can often hide there and then attack our plants. If you are not sure about your potting soil, you can also sterilize it in the oven. To do this, put the soil in the oven at 200 ° C for about 15 minutes. You can use the potting soil as normal for repotting your plants after it has cooled down. Pay attention to any changes to the roots, feeding spots or even larvae.

If weevils have spread anyway, you can use nematodes again or classic insect powder. You should again pay attention to the precise and safe application.

As already mentioned, you can also use the self-made trap made of a flower pot and some filling material (for example wood wool or straw) in your own four walls to catch and dispose of the uninvited guests. In general, however, it is very important to first identify the starting point of the tormentors in order to be able to fight them efficiently.

The black weevil is one of the most common species of weevil in Central Europe. In our special article you will find out how you can recognize and fight the black vine weevil.

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Kathi

I study phytomedicine in Vienna and grew up on a farm. So the diversity of nature has been with me all my life: from the large vegetable garden to our pasture areas. I am particularly interested in topics related to crop protection.
Favorite fruit: strawberry
Favorite vegetable: tomato