Weevils can cause great damage to plants. We'll show you how to identify and successfully combat this unwelcome pest.
The beetles with the typical shaped head can cause a lot of damage in the garden. The beetles of the Curculionidae family can grow from a few millimeters to two centimeters in size. Find out here what you need to know about these guests in your garden and what is best done against them.
Weevil: The Life Cycle
The life cycle of the approximately 800 weevil species in Germany is quite similar. The twilight and nocturnal beetles have a trunk-like pulled forward head, at the tip of which are the chewing mouthparts. The adult beetles have a dark, hard chitinous 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 weevil species reproduce parthenogenetically (unisexually). Therefore, in our latitudes, the beetles are mostly females who lay clusters of unfertilized eggs in the soil or in plant material, from which female weevils then hatch again. Up to 1,000 eggs can be laid per female.
The optimum soil 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-like shape and possess biting-chewing mouthparts. The larvae mine in plants or feed on the roots. Mining means that the larvae eat a mine or tunnel into the plants, so to speak. The tissue then dies around the burrows and turns brown.
The larval development depends on the temperature. In autumn the larvae reduce their feeding activity. Some species overwinter on the ground under dry leaves, others in the ground, and there are species thatseek hiding places under the bark of trees to spend the winter. Maturation feeding 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 sense vibrations, they drop to the ground.
Weevils in the garden: The most feared species
There are 50,000 species of weevils in total. This makes the Curculionidae family, which recently even includes the bark beetles feared in forestry, the most species-rich family of beetles. At the moment, the Rübenderbrüssler (Bothynoderes punctiventris) is making the headlines, as it severely affects sugar beets in Austria and poses major problems for agriculture. The following species can be particularly problematic in your garden or on your fruit trees. Rhododendrons in particular are often affected by weevil plagues.
Dreaded weevil species in the garden
- Red Vine Weevil (Otiorhynchus sulcatus)
- Like eating strawberries, raspberries, blackberries, currants, rhododendrons, roses, cyclamen and grapevines.
- Lesser or spotted cabbage weevil (Ceutorhynchus pallidactylus)
- Prefers to eat cruciferous vegetables, radishes, horseradish and canola.
- Red cabbage weevil (Ceutorhynchus napi)
- Loves to eat cabbage, radishes, horseradish and rapeseed.
- Red Weevil (Ceutorhynchus assimilis)
- Likes eating cabbage pods.
- Striped leaf-margin beetle (Sitona lineatus)
- Loves to eat peas, beans and clover.
- Carbon gall weevil (Ceutorhynchus pleurostigma)
- Loves to eat cabbage, radishes, horseradish and rapeseed.
Dreaded weevil species in the orchard
- Apple Blossom Weevil (Anthonomus pomorum)
- Occurs on apple trees.
- Weeping or Green Weevil (Phyllobius spp.)
- Occur on willow, rose, apricot, and plum trees.
- Pear Bud Bite (Anthonomus pyri)
- Occurs on pear trees.
- Strawberry blossom weevil (Anthonomus rubi)
- Occurs on strawberries, raspberries, and blackberries.
Portrait of the vine weevil
The Furrowed OneVine 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. However, this species also occurs on many different crops, from strawberries to our ornamental plants/shrubs and grapevines. Therefore this beetle is also called Black Vine Weevil in English.
The weevil is about 8 to 13 mm in size and has an elongated, oval body shape. It is dark gray to black in color, but has yellow scaly hairs on its elytra, which is why it appears irregularly spotted. The flightless beetle eats indentations in the leaves starting from the edge of the leaf. The larvae feed on the root hairs as soon as they hatch, later also on the root neck and can even debark the trunk base of trees. The larvae also penetrate tubers and eat them up completely. This underground feeding activity can cause your plants to wilt and die.
Portrait of the apple blossom cutter
If you have a garden near a forest and there are some apple or pear trees there, you might get problems with the small weevil (Anthonomus pomorum). A cold spring benefits this approximately 4 mm large beetle. It is light gray and has a light horizontal stripe on the elytra. The apple blossom weevil hibernates hidden on the trees or in the ground and begins feeding on its ripening in March. The beetles pierce the swelling buds and eat the escaping juice. After mating, the females continue to eat the closed flower buds and lay their eggs inside. The larva hatches after a few days and feeds inside the flower. You can recognize the damage caused by the apple blossom stinger because the eaten blossoms do not open, dry up and discolour.
Prevent weevil infestation: defend yourself instead of fighting
You can preventively protect your plants, bushes and trees from weevils. Especially if you have had problems with the voracious beetles before (e.g. last year), these tips can help you avoid damage.
Since most weevils are nocturnal or twilight active, the weevils look for dark places during the day where they can be foundto hide and sleep. Clever gardeners can take advantage of this behavior and lay wide wooden boards around endangered plants. The weevils then congregate under these boards. During the day you can then remove the boards and collect and eliminate the weevils sleeping underneath. Of course you won't catch all the beetles this way, but you can reduce the infestation pressure.
Extra tip: Another method of catching weevils is to use homemade traps in trees and bushes, but you can also use them indoors. In principle, these traps are similar to an insect hotel. To do this, take a flower pot, attach a string to the bottom to hang it up and fill it with wood wool, straw or something similar. Hang this trap in the garden and the bugs will use it as a hiding place. Then all you have to do is wait a little, check the traps regularly and get rid of the ravenous weevils. Just be careful not to kill any beneficial creatures that might also be in your trap.
Another preventive measure can be to keep the soil moist. The female weevils prefer loose and dry soil to lay their eggs. Regular and sufficient watering can therefore help. You can also disturb the larvae in the soil by hoeing and loosening more frequently. Encouraging weevils' natural enemies can also help with prevention. These include in particular birds, shrews and hedgehogs.
Fighting Weevils: Biological and Chemical Options
If weevils have invaded your garden and are causing damage, it's time to do something about the uninvited guests. Find out here which methods are available to combat them.
Control biological weevils
There are some effective biological methods for getting rid of weevils. The use of nematodes has proven particularly useful. These parasitize the larvae of weevils 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 catch boards, special boards are laid out here that 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 time to hunt for this is at night, since the weevils can be found at dusk or at nighttravel 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 proven method is hot water. Boil some water and then pour it into the bucket. This is how you can kill the beetle.
A biological pesticide is also suitable for controlling weevils. The active ingredient is azadirachtin, the plant protection product is better known under the name neem or neem. This natural pesticide is obtained from the seeds of the neem tree, has an inhibiting effect on egg and larvae development and can therefore be used against the larvae. You can pour the remedy for this. In addition, the agent is also effective against the adult beetles when sprayed.
Here we have summarized all biological control methods against weevils:
- 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. The insecticides may also have an effect on the nematodes. The following active ingredients are approved for home use:
- Thiacloprid Spinosyne A and D
- Deltamethrin Acetamiprid
Always read the instructions for use before using insecticides and follow the instructions. Personal protection and dosage are particularly important. If you dose insecticides or other pesticides too low, resistance can develop and none of us want a resistant weevil in our home garden.
Weevils in the home: fighting and preventing
If you grow 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 the soil in the oven. To do this, place the soil in the 200 °C oven for about 15 minutes. After it has cooled down, you can use the potting soil to repot your plants as usual. Pay attention to any changes to the roots, feeding sites oreven larvae.
If weevils have spread anyway, you can use nematodes again or classic insect powder. Again, you should pay attention to the exact and safe application.
As already mentioned, you can also use the self-made trap made of a flower pot and some filling material (e.g. wood shavings or straw) in your own four walls to catch and dispose of 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 vine weevil is one of the most common weevil species in Central Europe. Find out how to identify and combat the vine weevil in our special article.