Black Vine Weevil Control: Once you have pests such as the black vine weevils in your garden, it is often difficult to get rid of them. One simple, biological way to control the black vine weevil is with nematodes.
This article provides simple hints and tips on how to control black vine weevils. These are mainly active at night and leave characteristic feeding marks on plants such as rhododendrons, roses, clematis, or strawberries. More problematic than the unsightly feeding marks, however, are the larvae of the beetle, which damage plant roots.
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Identifying Black Weevil Infestation
If a garden is infested by thick-mouthed weevils, this can usually be recognized relatively easily by the semicircular feeding spots, the so-called bay feeding, on leaves of ornamental plants such as rhododendrons. The real problem for the plants, however, is not the nocturnal beetle, but its larva.
The larvae live in the soil, where they eat the roots of the plants and often even peel off the bark at the root neck. Thus, the plant is cut off from the supply of water and nutrients and may die. Therefore, once discovered, you should quickly begin to control the black vine weevil.
How to Get Rid of Black Vine Weevils and Larvae?
There isn’t much of a problem if you spot adult black vine weevils feeding on your garden plants while they are still in fewer numbers.
Your first priority should be killing the adults before they can lay eggs, which can take anywhere from 21 to 28 days of feeding. Hand-picking is a safe, albeit time-consuming, method of getting rid of a large number of black vine weevils at once.
When it gets dark, use a flashlight to find them, and then dump all of these black weevil pests into a tub of soapy water to finish them off. There may be something other than manual intervention that can get rid of all of your black vine weevils if hand-picking hasn’t worked or your plant is still suffering despite your efforts.
The application of nematodes against black weevils and their larvae is simple and does not require any special equipment. However, some points should be kept in mind: Because nematodes are sensitive to UV light, they should only be applied in the morning or evening and under overcast conditions. The required soil temperature of 12 °C is important for effective reproduction of the nematodes and thus for successful application.
When storing nematode preparations, keep in mind that they are living organisms. Apply the beneficial organisms as soon as possible after receiving them. When stored in the refrigerator, nematodes can be kept for a maximum of 6 weeks.
Important Considerations while using Nematodes
Before deciding to use biological agents like nematodes to combat pests, you should consider the following important questions.
What is the Best Time to use Nematodes to kill Black Weevil Larvae?
During the year, there are two phases in which the control of black vine weevils with nematodes is recommended: In spring from April to May or in late summer between August and September. The condition is that the soil temperature is above 12 °C for a few hours every day.
These recommendations are based on the life cycle of the beetle and the temperature requirements of the nematodes. To achieve complete control, it is advisable to treat once in spring and once in late summer.
Appropriate nematodes are effective only against black vine weevil larvae and pupae, but not against the beetles or eggs of the black vine weevil. Early treatment kills the pupae and then, in the fall, the newly hatched larvae. After application, the first larvae of the black vine weevil die within 7 days.
As the nematodes continue to multiply in the insects, the control success increases over time, so that a suitable long-term effect is achieved depending on the infestation level.
Which Nematodes can be used to Get Rid of Black Vine Weevil Infestation?
An example of nematodes that are effective against both the pupae and the larvae of the black vine weevils and it’s larvae are HB Nematodes. HB nematodes are tiny organisms of the species Heterorhabditis Bacteriophora, which are about 0.6 mm in size.
In the soil, they seek out and invade larvae and pupae of the pests. There, the nematodes continue to multiply and kill the infested larvae or pupae. Eventually, the nematodes leave their host and infest more larvae.
#Tip: In addition to controlling black vine weevil larvae, HB nematodes can also help control white grubs that cause turf damage.
Because HB nematodes specialize in only a few pests, they pose no threat to warm-blooded animals, humans, or garden plants. So, you also don’t have to worry about the unwanted spread of nematodes in your garden.
As soon as the work of the nematodes is done, i.e. there are no more pupae and larvae of the black vine weevil in your garden, the number of nematodes also decreases more and more. However, HB nematodes can also form longer-lived survivors, so some long-term protection remains.
Note: There are other nematodes that can be used to control black grubs. For example, nematodes of the species Steinernema kraussei parasitize mainly larvae, whereas Steinernema carpocapsae attack the adult beetles. HB nematodes, however, are most commonly used because of their good efficacy.
How to use Nematodes to get rid of Black Vine Weevil Pests?
You can follow these instructions to achieve the best results in controlling and killing Black Weevils and Larvae.
- Water the soil thoroughly.
- Select the appropriate nematode product.
- Mix the Nematode product with water as per the instructions on the package and the area to be treated.
- Keep stirring mixture vigorously or else nematodes will settle to the bottom.
- Pour finished mixture into a garden watering can or nematode sprayer and distribute evenly.
- Immediately after application, pour with at least 1 L of water per square meter to flush down nematodes from grass and plants into the soil, if necessary.
- Do not allow treated soil to dry out for at least the next 4-6 weeks, as nematodes require moist and wet soil to survive.
The information given relates primarily to HB nematodes against black vine weevils. There may be different application instructions for other products.