Crawling in the garden and holes in the rose petals – the alarm bells are already ringing for hobby gardeners who are more remote from nature. Don’t panic, we will tell you who is crawling and nibbling there, how you can fight this vine weevil and how you can design your garden in such a way that you no longer have to fear such bugs and many other pests in the long run.

The first step – identify vine weevils

If you’ve been spotting eaten leaves in your garden, namely leaves that have neat crescents or neat arches bitten into the leaf edges, you should be on the lookout for a black vine weevil. This Beetle is famous for the fact that it works extremely well, it is also called “ticket clippers” because of the accuracy of its semicircles.

The black weevil is barely to a good centimeter tall, like almost every beetle, oblong oval and quite dark in color (just like rich, moist garden soil). On the back it has longitudinal furrows and pale yellow flaky hairs. Otherwise it has 6 legs and a really thick trunk, like an elephant, pointing downwards. Since the black weevil is much smaller than an elephant and the trunk is also much shorter in proportion, you must have considerable visual acuity if you want to identify the beetle by this characteristic. The overall impression when something is crawling around in the bed (black weevils cannot fly) is more helpful, and the “crawling time”: black weevils are active at dawn.

The vine weevils that you see will only ever be females – this beetle has made itself independent of the often difficult sexual reproduction and relies on parthenogenesis, i.e. virgin generation. When such a virgin generation takes place, only females emerge from it. Whether there are (still) male vine weevils does not seem to be entirely clear, although photos of clear “mating positions” can be found (the author would be happy to receive information from a specialist). In any case, these females lay eggs on the root neck of their favorite plants (see prevention below), up to 1,000 per female. The more favorable the conditions, the more larvae hatch and survive, The larvae have the best chances at soil temperatures between 16 and 27 degrees and a high level of moisture in the soil. The larvae are white with a small brown cap on the head, have wrinkled skin and usually curve inwards. They grow to be a good one centimeter long.

The black weevil itself lives up to two years, nestling in root balls for the winter. During this time he produced offspring twice. The larvae develop differently over the summer depending on the temperature, soil moisture and food supply, in autumn they reduce their feeding activity, the larvae that have already developed sufficiently now also overwinter in the root area. In the spring they only eat a little strength again, in order to pupate in April / May and after around three weeks to hatch the next generation of beetles, which now start eating their plants with fresh energy. If vine weevils have made their home in a greenhouse or winter garden, they can do without hibernation, as it is warm enough here.

The damage caused by the black weevil

Immediately after hatching, the larvae begin to damage the fine root hairs of their host plants. As they get older, they also nibble on larger parts of the roots, at the root neck and at the base of the root, if they are numerous, they completely debark the roots. The larvae then gnaw the lower parts of the plant and penetrate the inside of plant tubers, which they then simply hollow out, e.g. B. in cyclamen and tuberous begonias. The damage in the root area leads to stunted growth in woody plants and to wilting in herbaceous plants; if too many larvae eat, the plants die.

The adult beetles can usually not do so much with their bay food if they (are allowed to) become very numerous, but they also go on buds or on shoots or gnaw off the bark.

How to prevent an infestation

When vine weevils come across a natural garden and strong plants, they will hardly be noticeable any further. If not, because they can nestle in a monoculture garden and then perhaps find favorable conditions, you will have a busy time ahead of you before you get the beetles under control. Therefore (and because the black weevil are growing, see below) certain measures are recommended for every enthusiastic gardener, with some specifically preventing the black weevil and others simply ensuring that your plants are better equipped against diseases and pests:

  1. The prevention of the black weevil begins with the purchase: it is best to buy your plants from specialist companies and not from occasional dealers, here you have a much better chance that you will receive pest-free plants. In addition, check the plants yourself when purchasing them to see whether they or the surrounding plants have pitting at their roots or pits, and watch out for larvae or feeding marks later when planting them.
  2. Buy organically grown, strong native plants in your region that will feel good in your garden and not exotic or beauty-grown but weak hybrids.
  3. Support your plants with plant strengtheners, various commercially available mixtures and self-made alkaline solutions come into consideration. Environmentally friendly plant strengtheners with silicon are said to help against the black weevil, which improve the plants’ resistance to the pests. Watering with wormwood slurry diluted in a ratio of 1 to 10 is also supposed to drive away the appetite of the black weevil larvae, to keep ants and snails off and to fertilize the plant.
  4. Design your garden so naturally that numerous beneficial insects such as shrews and millipedes, hedgehogs and spiders, ground beetles and insectivorous vertebrates feel comfortable in it. If you provide these beneficial insects with sufficiently favorable conditions through a few piles of branches and other hiding places, you will probably never get to know the black vine weevil. Do not use peat-containing substrates, which not only damage the moors, but also offer the black weevil ideal living conditions.
  5. Frequent tillage can disturb the black weevil and its larvae. This does not mean that you should start digging up again, which has long been frowned upon, and thereby turn the ecosystem in yours upside down. Rather, you can also practice gentle soil care that does not disturb the soil organisms: You can loosen the soil with the digging fork or garden claw by just piercing these tools into the soil, moving a little and pulling them out again.
  6. If an infestation is already suspected, you should perhaps change your planting plan and not just “put its favorite plants in front of the vine weevil’s nose” (sorry, in front of the proboscis). Weevils like (same with house and greenhouse plants): cyclamen and azaleas, begonias and garden chrysanthemums, clematis and thick-leaf plants, ivy and yews, strawberries and ferns, lilacs and fuchsias, gloxinias and heather plants, hydrangeas and camellias, laurels and lilies, laurels , Rhododendrons and roses, slants and taxus and grapevines. Incidentally, the fact that the beetles cannot fly does not protect your potted plants and balcony plants in the least, because as a counterbalance they are incredibly good on foot and can effortlessly climb even the smoothest walls or window panes.
  7. The black weevil loves the Flaming Käthchen (Kalanchoe blossfeldiana) so much that you can use it as a catching plant: Simply place it next to an endangered plant and let the black weevil wander towards its destruction in a concentrated manner. Contrary to popular belief, this can also be done in the garden, particularly robust outdoor varieties are sold as “outdoor” kalanchoes.
  8. Also in acute danger, the following measure could bring last-minute help: If the weather in May or June gives you the opportunity, let your garden dry out for a few days as much as you think your plants can. A plant needs a few days before it suffers seriously from drought, the larvae, which are considerably less voluminous, will probably dry out faster.

Because today many traders deal in plants that lack the necessary specialist knowledge, harmful camouflage artists such as the black weevil can spread more and more, and because our gardens and horticultural companies are far too seldom ecologically in balance, there is no defensive potential here. Help us to do something about it!

Fight vine weevils by collecting them

When the vine weevil is already there, the best time to control the adult beetles is when they are ripe. It begins in May / June and lasts one to two months, only then have the beetles developed eggs that they now want to lay. So you have some time to fight the beetles, as they cannot fly, you can confine yourself to a fairly narrow area – “good walking” does not mean that the beetles can travel long distances. You can do that:

  • During the ripening process you can spoil the beetle’s appetite with tansy tea, quassia broth or soft soap solution, the preparations are sprayed extensively on the plants and the surrounding area.
  • You can also go into the garden with a flashlight at dusk and collect beetles, or collect them when the population is just building up, which is definitely successful.
  • You can lay out brittle and well-soaked boards or thick, moistened cardboard under the plants, here the beetle will crawl after eating and can be removed during the day. To do this, take a bowl with a smooth rim and the largest possible diameter with you and strip off the underside of the board or cardboard at the edge, then the beetles will fall into the bowl.

Control the black weevil larvae with nematodes

If it turns out that in spite of all preventive measures and in spite of all “beetle-gathering” larvae have been developed, you can fight them biologically: You can use special nematodes that actively penetrate the pests (and only them) and leave bacteria there, which then multiply in the larvae and kill them. The rendered harmless larva now changes color from white to reddish or brown-orange, the nematodes first multiply in the larva and then swarm out and destroy the next larva.

The nematodes, which like black weevil larvae, are available (to order) in gardening shops, they are called “Heterorhabditis bacteriophora” and are used as follows:

  • The soil should have a temperature of at least 12 degrees, otherwise the nematodes will die.
  • They eat the larvae and pupae of the black weevil, regardless of the soil temperature, which results in recommended application times between the beginning of April and the end of May and between the end of August and the beginning of October.
  • The soil should be kept well moist during the 10-day activity of the nematodes, so that the nematodes can move best.
  • The roundworms are delivered embedded in clay mineral, the whole thing is simply dissolved in water and poured out with a watering can.
  • The package states a certain amount that must be applied in order for the nematodes to do their job successfully
  • Nematodes must not be distributed in full sunshine as they suffer from UV rays

Fighting black weevils with chemicals?

Caution, one can only say, the utmost caution, because in this case the use of chemicals could fully hit people back:

  • According to the information sheets of many plant protection offices, there are no effective chemical preparations against the black weevil, even if some commercial preparations claim the opposite.
  • These commercial preparations are or were in some cases even approved as pesticides for home and allotment gardens, but without exception they contain the active ingredients thiamethoxam, imidacloprid or thiacloprid.

At the beginning of 2013, the EU Commission recommended banning the insecticides thiamethoxam and imidacloprid (and clothianidin) because a study by the European Food Safety Authority (EFSA) has shown that these pesticides are partly responsible for the rampant bee deaths. How the implementation will take place remains to be seen and observed – according to the recommendation of the EFSA, these funds should initially only be banned for two years, which suggests considerable influence of the lobby of the pesticide industry.

Thiacloprid is less toxic to bees, even 1000 times less toxic, and yet a research project has been running since May 2012 that will investigate the long-term effects of thiacloprid on bees in more detail until summer 2014.

When researchers see an opportunity to examine the toxicity of the substance, which is a thousand times weaker, for three years, one really does not want to imagine exactly what the strong poison does. Anyone who would still like to have plants to eat in a few years’ time and knows that bees are needed as pollinators will not touch such products.

An acute and severe infestation by the black weevil has to be combated very labor-intensive. However, if you design your garden so close to nature “that it can defend itself against pests such as the black weevil”, you save costs and work and also help in general to maintain the biological balance.

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