the essentials in brief
- Black weevils can be best combated by collecting them and / or using nematodes
- The pests do not like the smell of neem oil
- Beneficial organisms such as moles, hedgehogs and shrews prefer to eat the insects
- Insects do not like loose, peat-rich soil
Fight black weevils effectively
Continuity is important for successfully combating the extremely stubborn pest, because the infestation cannot be contained with a single measure. The animals reproduce too quickly and too numerous for you to catch them all at once.
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By collecting it by hand, weevil infestation can be combated quite well. However, you can only catch the nocturnal beetles late in the evening or at night, preferably during the summer months between May and August. Take a flashlight with you to catch the animals doing their nocturnal activities - and be as calm as possible. Ultimately, black weevils perceive the finest vibrations through their leg hairs and flee when danger threatens.
Collection can also be made easier if you place Flaming Cathies (bot. Kalanchoe blossfeldiana) next to infested or endangered plants, which the vine weevils particularly love. Many of the beetles will migrate to this plant and are easier to catch.
Fight biologically with nematodes
If the black weevil infestation is already very pronounced and your plants are plagued by the countless larvae, biological control of the animals with the help of nematodes helps. These are tiny roundworms with the name Heterorhabditis bacteriophora, which you can buy from well-known suppliers such as Bayer or Neudorff in specialist gardeners or simply order from Amazon. Nematodes destroy the vine weevil larvae by penetrating them and leaving bacteria there that are deadly for the beetle maggots. The plant is not damaged in the process.
In order to destroy the larvae in a targeted manner, precise dosing of the nematodes is necessary. Depending on the square meter treated, you should apply around half a million roundworms. If possible, distribute them as soon as possible, as the tiny ones die off quickly. However, they usually last a few days if you store them in a cool place. Nematodes need moisture to be active. The following video shows how to properly deploy the animals:Youtube
It is best to proceed according to this scheme when applying the roundworms:
- First, water penetrating the soil to be treated.
- Do the watering early in the morning on a warm summer day.
- Wait until the evening.
- Pour the nematodes from the packaging into a watering can filled with water.
- Stir gently.
- Use the mixture to water the root area around the plants to be treated.
- Keep the floor area evenly moist for the following weeks.
- However, avoid waterlogging, as neither plants nor nematodes can tolerate it.
Application in the dim evening hours is important because the beneficial animals are very sensitive to UV light. Ideally, the floor should also have a temperature between 15 and 25 ° C so that the nematodes feel comfortable in it.
In the meantime there are also trapping boards coated with nematode-containing gel that contain the species Steinernema carpocapsae and with whose help you can catch and destroy the adult beetles. Simply place the traps under the infested plants between May and September, the beetles will visit them as a welcome hiding place during the day and will quickly be attacked by the roundworms.
When using nematodes, however, it is not just the way they are used, but above all the timing that is important. Most products are only effective at floor temperatures of 12 degrees Celsius or more, which must be maintained over a period of four hours a day. Under this condition, there are two possible treatment periods in the year during which the nematodes can work particularly successfully:
- April / May : in the spring you control overwintering larvae, pupae and beetles
- August / September : in late summer the nematodes kill larvae in various stages
Infested plants in the home, on the other hand, can be treated all year round because there is no frost here.
Neem press cake / neem oil
Neem oil, which is obtained from the seeds of the Indian neem or neem tree (bot. Azadirachta indica), is an important pesticide. The natural insecticide contains the substance azadirachtin, which prevents pests from multiplying and thus lets them die. The remedy is also very effective against the black weevil, whereby you can use neem press cake - these are the residues that are left over during the production of the oil - for easier application.
Work this flat into the soil around the plant, which you should repeat over and over again every two months. Calculate a consumption of around 50 grams per square meter of surface. The plants take up the active ingredients from the press cake, so that both the larvae and the adult beetles gradually cease to eat.
Do not use neem products and nematodes at the same timeAs is so often the case with neem products, what works against pests often also kills beneficial insects. The ingredients in neem oil are also highly toxic to nematodes, which is why you should not apply the roundworms at the same time as the insecticide.
Basically, every garden owner should be happy who has hedgehogs, moles, shrews, common toads or lizards in the garden: These animals like the adult weevils and their larvae to eat and thus keep the population low. If you create refuges and hiding places for these animals, the voracious beetle has no chance. Free-roaming chickens also like to scratch for the nutritious larvae, but they cannot be used everywhere in the garden. The poultry do not only eat the pests, but also all kinds of vegetables and fruit.
This is how you recognize a black vine infestation in good time
Since the black weevil has a wide host range, it quickly eats its way through the garden and attacks a large number of different plant species. However, it has some preferred food plants and nests itself mainly in rhododendrons, cherry laurel, hydrangeas, roses, berries, yew and bergenia. But many other shrubs and trees are also on his menu.
The feeding damage also manifests itself in two ways. The adult beetles feed on the above-ground parts of the plant, while the larvae feast on the roots and other subterranean parts of the infested plant. The beetle damage is quite easy to recognize because the adult animals eat real bays in the leaf margins. On the other hand, it is much more difficult to identify larvae infestation, because here the damage pattern appears to be quite inconsistent. The table clearly shows you which symptoms indicate a black weevil infestation:
|Stage of development||Above-ground damage||Underground damage||Effects on the plant|
|Imago (adult beetle)||Arched pens on the leaf margins, damage to the bark and shoot tips||usually none||poor condition, little growth, hardly any development, leaf discoloration, wilting|
|larva||Feeding marks on stems and trunk close to the ground||pitted roots, pitted root neck, debarked roots, hollowed out tubers and rhizomes||Wilt, stunted growth, leaf discoloration|
If you suspect an infestation with black weevil larvae in withered plants, you have to look in the root area. The small, white maggots are often found here in great numbers. It is important to act as quickly as possible when an infestation is identified in order to prevent further damage and even death of the plant.
Check potted plants after winter
Unfortunately, the black weevil not only feels at home in the garden, but also in potted plants - regardless of whether they are in the winter garden, on the balcony or in the room. In most cases, indoor and other potted plants are attacked by potting soil contaminated with eggs and / or larvae. You should therefore carefully check potted plants with the described damage patterns for any beetle larvae or even adult beetles. Such a control is particularly important when clearing the winter quarters in order to prevent further spread in good time.
Prevention is better than fighting
So that you do not get a problem with the black vine weevil in the first place, you should prevent an infestation. A few measures help here, which make life difficult for the pest and therefore can hardly reproduce:
- Avoid potting soil containing peat for potted plants
- Often work the garden soil gently with a hoe or digging fork (do not damage the roots!)
- Careful pricking into the ground with the digging fork is sufficient
- Refrain from mulching, instead pull weeds more often
- Keeping chickens - the larvae of the black weevil prefer to pick them out
- Water plants regularly with plant strengtheners
- Tansy or wormwood manure are particularly suitable
Make and use tansy or wormwood manure
Tansy and wormwood can be used to easily produce non-toxic, but nevertheless effective plant strengtheners that not only drive away the black weevil. Tansy, for example, also helps against aphids, whiteflies and other leaf sap suckers as well as against downy mildew, which often occurs in the garden. Wormwood, on the other hand, also helps against rust diseases and mites. Both plants can be found in nature, especially the tansy is common in the summer months at the edges of fields and roads and can be easily recognized by the bright yellow button flowers. Collect the flowering herb whole and either use it fresh or dry as a supply for later use.
Preparation of the plant manure in the step-by-step instructions:
- Crush one kilogram of plant matter (leaves, flowers, stems)
- Fill this into a plastic bucket.
- Do not use a metal container as this can cause undesirable chemical reactions.
- Pour 10 liters of cold water over the plant material.
- Add a handful of rock flour (€ 14.95 at Amazon *), this will bind the odor that will later develop during fermentation.
- Put the bucket in a dark and warm place.
- Cover it with a breathable net or something similar
- But don't put a lid on.
- Let the mass ferment for 10 to 14 days.
- Stir the liquid manure daily with a wooden stick.
The liquid manure is ready as soon as no more bubbles rise or the liquid no longer foams. Now dilute it 1:10 with water and water the endangered plants with it at regular intervals.
Instead of liquid manure, a brew also helps very well. Boil 300 grams of fresh or dried herb in one liter of water for half an hour, then strain off the solids. Let the brew cool down, dilute it 1:10 with water and water or spray the plants with it. The liquid can be kept hot for several months when filled into a screw-top jar or a well-sealable glass bottle.
Way of life and reproduction
However, the pests are rarely seen, because black weevils are both nocturnal and fast. The flightless animals are excellent at climbing and can perceive even the finest vibrations through special hairs on their front legs. As a result, they quickly recognize approaching dangers, simply drop on the ground and hide. Even during the daytime, the animals spend their time in protective hiding places near the infested plants, preferably in the mulch, in leaves or buried in the upper layer of the earth.
The animals only become active at twilight, when they climb up the plants and enjoy the leaves, shoots and buds of herbaceous plants. In contrast to many other insects, adult vine weevils live to a fairly old age and can live up to 12 months.
Development of the larvae
While the adult beetles show their first signs of feeding in spring, the larvae only become active late. The eggs are laid in the open quite late between July and October, whereby the females do not have to be fertilized. Instead, the pest usually reproduces through parthenogenesis, i.e. through first generation. The round, white eggs, which are not even a millimeter in diameter, are laid in packets near the host plants, with each female beetle laying down up to 1000 eggs.
The larvae, which are quite similar but significantly smaller, hatch after about three weeks and spend their entire larval phase underground. How fast (or slowly) they go through the various stages of their development depends heavily on external conditions. These weather conditions are ideal for rapid pupation and thus even faster reproduction:
- Temperatures between 16 and 27 ° C
- sufficient soil moisture
- no drought
In favorable weather the larval phase lasts only two months, in unfavorable conditions, however, the pest can remain in this stage for up to 12 months. The maggots overwinter without any problems in the field and become active again in spring. There is only one generation per year, with the exception of greenhouse and winter garden crops: here the animals do not take a winter break due to the favorable temperatures.
What does the black weevil do in winter?Black weevils overwinter as adult beetles and also as non-pupated larvae, mainly in the root area of their host plants, which they visit when autumn temperatures drop. But other hiding places, especially underground ones, are also possible, for example in a thick layer of mulch or leaves that the gardener has left in preparation for winter. Here the beetles fall into a frozen state from which they only wake up and become active again in April or May - depending on the weather. The animals hidden underground are usually not affected by frost.
What are black weevils?
Black weevil (lat. Otiorhynchus) are a genus of beetles from the family of weevils (lat. Curculionidae), which cause great damage both in agriculture and in hobby gardens. Both the adults, known as adults, and their larvae have a great appetite. While the adult beetles live above ground and feed mainly on leaves, young shoots and buds, the grubs are in the ground and eat roots, rhizomes and tubers there.
The black weevil genus is very species-rich and includes around 1000 different species. The furrowed black weevil (lat. Otiorhynchus sulcatus) occurs as a pest in the garden. The species is not very specialized in certain types of plants. In addition, the following species make life difficult for the gardener:
|Art||Scientific name||distribution||Characteristics beetle||Larvae||Preferred plants|
|Furrowed vine weevil||Otiorhynchus sulcatus||originally Europe, now almost worldwide in temperate regions||black with brown spots, about an inch long, unable to fly||yellowish-white, brown head capsule, about one centimeter long, curved||little specialized, preferably rhododendrons, cherry laurel, hydrangeas, yew trees, euke cones|
|Bristly vine weevil||Otiorhynchus scaber||originally North America, introduced also in Europe||spotted brown, about an inch long, unable to fly||yellowish-white, brown head capsule, about one centimeter long, curved||little specialized, preferably rhododendrons, cherry laurel, hydrangeas, yew trees|
|Little black weevil or strawberry root weevil||Otiorhynchus ovatus||Northern and Central Europe, North America, in lowlands||black with longitudinal wrinkles and parallel rows of dots, up to five millimeters long||whitish, red-brown head capsule, up to six millimeters long, curved||Spruce, spruce forests|
|Big black weevil||Otiorhynchus coecus||Low mountain ranges and Alps, mainly Europe||black with reddish legs, longitudinal wrinkles and parallel rows of dots, up to one centimeter long||whitish, red-brown head capsule, up to an inch long, curved||Spruce, spruce forests|
|Lucerne weevil||Otiorhynchus ligustici||all of Europe, North America||up to 12 millimeters in length, great variance in appearance, mostly brown||whitish with a brown head capsule, up to an inch long||Vineyards, fields, meadows, mainly eat clover and alfalfa|
Due to the great importance of the furrowed black weevil, the article only deals with this, but the different species are very similar in terms of their biology and possible control options.
Appearance of the black weevil
The furrowed black weevil has a characteristic appearance of beetles, which has the following features:
- Legs : three jointed pairs of legs
- Upper wing : armor-like, strongly arched
- Color : dark to brown, without a metallic sheen
- Size : up to 12 millimeters long
- Special features : granular or corrugated back, often with yellow or brown dots
- Proboscis : strong, twice as long as wide, lobe-like enlargements
- Larvae : legless, yellowish-white, brown head capsule
- Larva size : about one centimeter, crooked posture is typical
Are there any effective insecticides against the black weevil?
Toxins in the garden not only kill pests, but also destroy beneficial insects and damage biological diversity.
Commercially available chemical sprays such as thiacloprid, imidacloprid or thiamethoxam are expressly not recommended for use in the garden, as they not only fight the black weevil - on the contrary, they destroy the delicate biological balance and can cause considerable damage to flora and fauna.
For example, these funds are held responsible for the death of bees - with the result that fruit trees and other plants that rely on pollination bear little or no fruit at all. For this reason, refrain from using toxic pesticides such as these, because you have enough effective biological preparations on hand against pests such as the black weevil.
frequently asked Questions
Is it true that coffee grounds help against vine weevils?
In fact, dried coffee grounds are both a good fertilizer and an old home remedy for the black weevil. Since the remedy is not very effective in comparison to other preparations, you should not rely on them alone.
Does garlic help against the vine weevil?
Garlic is also one of the plants that the vine weevil does not like. As a result, you can counteract an infestation with garlic broth or stock just as effectively as with a remedy made from tansy or wormwood. The remedy also helps against many other pests (for example against aphids, thrips or spider mites) as well as against various plant diseases. And this is how you make the brew:
- Crush 3 to 5 large, fresh cloves of garlic into small pieces.
- Put the garlic in a container.
- Pour a liter of hot, but no longer boiling, water over it.
- If the water is hard, add a splash of fruit vinegar.
- Let the brew stand in a warm and dark place for 24 hours.
- Sieve off the brew and fill it up to one liter with water.
- Fill it into a boiled, sealable glass bottle or a screw-top jar.
- Water or spray endangered or infested plants with it.
- Repeat the application at regular intervals.
How can I build a trap myself?
You make it easier to collect the beetles at night if you build this one trap. For this purpose, place flower pots filled with wood wool or thick, well-moistened cardboard directly under the infested plants. During the day, the pests like to take these as hiding places and can thus be caught in a targeted manner. Alternatively, rotten, well-soaked boards also help.
Why does the black weevil treatment not help?
If the black weevil infestation occurs again and again despite repeated treatments, it is usually not the supposedly ineffective remedy to blame. Instead, there could be various reasons why the measures were not successful:
1.) The treatment was not carried out often and / or tightly enough so that some larvae and / or beetles have survived and are now proliferating.
Countermeasure: Repeat the treatment, but this time more closely and over a larger area.
2.) Beetles and / or larvae have survived in hiding places not covered by the treatment, perhaps even overwintered, and have migrated from there.
Countermeasure: Remove any hiding places (including plant pots, boxes and the like!) And treat them thoroughly.
3.) Adult bugs have migrated into yours from outside, for example from your neighbors' garden.
Countermeasure: Treat your plants again and make your neighbors aware of any black weevil infestation.
Unfortunately, the fact is that, despite the available effective means, the black weevil can recur. The animals are simply too willing to reproduce and are not well adapted to certain plants to be able to kill them in an uncomplicated manner. One remaining larva is sufficient, which pupates the following year and in turn lays 1,000 eggs - and the big eating is already underway again.
Even if your garden plants seem to wither for no reason, the black weevil is not always behind it. Instead, such wilting can have many different causes, which are often due to incorrect care and / or an unsuitable location.