The Content Of The Article:
- Larvae destroy the roots
- Combat by collecting
- Biological control with nematodes
- Apply Nematodes: It depends on the time
- Neempresskuchen spoils the appetite
- Promote natural enemies
At the top of the menu of the Fringed Weevil (Otiorhynchus sulcatus) are shrubs with slightly coarser leaves such as rhododendron, cherry laurel, boxwood and roses. The beetles are not very picky and also like to eat strawberries, potted plants such as angelic trumpets and Mandevillen as well as clematis and many different perennials. At the characteristic bastard feeding, semicircular feeding along the leaf margins, you can see that a Black-weevil is doing its job.
Bittern feeding on a Bergenia leaf caused by black-backed weevil
Larvae destroy the roots
The feeding damage of the beetles are not nice to look at, but represent no serious threat to the plants. More dangerous are the larvae of the weevil: they live in the root area of the plants mentioned and eat first the important for water absorption fine roots. Older larvae often work their way to the root base, where they nibble the soft bark of the main roots. If the larvae themselves do not kill the plants, there is still the risk of infection with soil fungi such as Verticillium. These can penetrate into the plants via the feeding sites at the roots.
The larvae of the weevil are living in the soil. They are light and legless
For optimal control of the weevil it is important to know its life cycle. Its development time depends heavily on the weather. The first black-backed weevils hatch in May, the last often in August. They are almost exclusively female animals that after a short period of maturation without mating from the end of May to August up to 800 eggs. As oviposition sites, they prefer sandy, preferably humus rich soils in the root area of the host plants. Two to three weeks after oviposition, the first larvae hatch and begin to eat immediately. They hibernate in the ground and pupate from April. About three weeks after pupation, the first young beetles free themselves from the pupal shell.
The grasshopper's larvae live in the ground and eat at the roots of the plants. The adult beetles cause the typical battening on the leaves
Combat by collecting
Adult weevils are difficult to control with contact insecticides because they live very hidden. For infestation control you can best feel it in the dark with a flashlight. If you have discovered beetles, it is best to place flower pots filled with wood wool underneath the infested plants. The beetles hide in it during the day and can be collected.
Biological control with nematodes
Most effective is the control of larvae with parasitic nematodes. The roundworms of the genus Heterorhabditis are about 0.1 millimeters long - so you can see them only under the microscope. They actively move in the bottom water to the larvae and penetrate through the skin and body openings. In the larva, the nematodes secrete a bacteria that is harmless to humans and animals, and kill the larvae within three days. The nematodes have a very long-lasting effect, as the parasites continue to multiply in the body of the dead black weevil larva - up to 300,000 new nematodes are created in each larva.
Apply Nematodes: It depends on the time
HM nematode under the microscope
The months of April and May as well as August and September are optimal for controlling the weevil larvae. For nematodes with the trade name "HM-Nematoden" you can buy order cards in the garden center. The fresh nematodes are then delivered directly to your home in a plastic bag with special carrier powder. You need 500,000 nematodes per square meter, the smallest package size is enough for about six square meters.
The thread worms should be applied as soon as possible, but can survive in cool storage quite a few days in a plastic bag. Before application, you must thoroughly water the plants to be treated. The roundworms need enough moisture in the soil to move around, but they do not tolerate waterlogging at all. On a warm summer's day, soak in the morning so that the floor can warm up again. The soil temperature should not be below twelve degrees, optimally 15 to 25 degrees.
With a dosing system on the garden hose, the nematode solution is targeted against the larvae of the weevil
The nematodes are best brought out only in the evening or in cloudy skies, because they are very sensitive to UV light. Fill the contents of the bag into a watering can with stale tap water or groundwater and pour the root area around the infested plants.For the nematodes to work optimally, you should also water regularly for the next six to eight weeks. As weevils can turn three years old, it makes sense to repeat the nematode treatment over the next two years. In the meantime there are also special dosing systems in the garden trade, with which the nematodes can be easily deployed.
Neempresskuchen spoils the appetite
To prevent feeding damage to the plants, you can incorporate Neempresskuchen flat in the soil around the plant. These are squeezed seeds of the neem tree. In addition to various nutrients, they contain about six percent of neem oil, which is toxic to insects. The active substance is absorbed by the plant and causes the beetles and also the larvae to stop their feeding activity. Deliver about 50 grams per square meter and sprinkle this amount about every two months - the best year-round for thawing and evergreen plants. But beware: Neem also works against nematodes. Never use neem press cake if you have fought the weevil larvae with HM nematodes.
Promote natural enemies
The black-eared weevil has many enemies, including shrews, hedgehogs, moles, lizards, common toads and various garden birds. These animals can help you by providing ample shelter and nesting opportunities. Thus, a natural balance can be established over time. Free-range chickens also help to stem the weevil plague in the garden.