How to spot and control vine weevil in your glasshouse

Learn how to eradicate vine weevil and their larvae.

Scientific name for vine weevil: Otiorhynchus sulcatus.

Vine weevil (or, more specifically, their larvae) are my nemesis. I am going to tell you how to get rid of them.

I know first hand just how destructive an infestation of vine weevil can be to your potted plants, once their eggs start hatching. Unfortunately, I have become experienced in spotting the tell tale signs of a larvae or two nibbling away at the roots of my beloved plants

Let’s take a look at the little grubs in a bit more detail and more importantly, find out ways to deal with them –

Facts about vine weevil:

Adults 

• Adult Vine Weevils are dark-coloured, wingless beetles, most active at night.
• They are ALL female - this means that they do not require a male to reproduce. This makes them particularly prolific at reproducing. One of these ladies can lay a thousand eggs in a season.
• Vine weevil egg are tiny, brown and near enough impossible to see without the help of a magnifying glass. They are laid in summer through to early autumn, on the surface of the soil.
• There are thought to be 60,000 species of weevil. Not all of them are considered a pest and not all of them do damage to plants. 
• The plant damage the adults do is not life threatening to the plant, but the energy they get from eating the leaves does give them the energy required to lay their eggs...so in turn leads to extreme vandalism.

Larvae

• The larvae eggs hatch out in late autumn and winter and the larvae eat the roots of the plant. 
• The larvae are small, 1cm sized, c-shaped, legless grubs. They are cream coloured with a brown head.
• They overwinter in the soil, laying dormant until they pupate and emerge as an adult in the springtime. 
• They are a particular pest for plants grown in containers, but they can, unfortunately, cause havoc in borders too.

Plants most affected by vine weevil

• Adult beetles are especially fond of shrubs and tough herbaceous plants such as Euonymus, Rhododendron, Hydrangea, Primula, and Bergenia.
• Plants grown in containers and undercover are at particular risk.
• Succulents and plants with fleshy stems/leaves are susceptible to vine weevil attack. E.g. Sedum and Cyclamen.

• Notches in the leaves - Look for signs of damage on the leaves of your plant. Adult Vine Weevil nibble away at the edges of leaves creating distinctive, notch-shaped bite marks around the borders.
• Yellowing leaves - Plants turn yellow and wilt. This could be down to improper watering, but if you think you have watered your plant correctly, you may have a naughty Vine Weevil grub eating the roots.
• Collapsing plants - Plants that yellow, wilt and then collapse for no apparent reason may be subject to a Vine Weevil larvae attack. The larvae happily hatch out in the soil, and chomp away at the root system. The plant collapses as it can no longer take up the water or nutrients it requires to live. 

Control methods and treatment of Vine Weevil:

• Physical control - Remove the adults before they have a chance to lay their eggs. As the adults are nearly always resistant to insecticides and chemicals, it is best to pick them off and remove them, by hand. Vine weevil come out at night, so are easiest to spot at dusk/nighttime when they are feeding. Go “hunting” by torchlight and tap your plants over a piece of newspaper to shake them off. They can’t fly so the paper will catch them and you can then squish them and throw them away. This is an effective, eco friendly method of control.

• Chemical control - As I mentioned earlier, I do not like using insecticides generally, but if you’re faced with a real infestation of adult larvae in the roots, the only way really to get rid of them is to drench the compost with a commercial, systemic insecticide. Treat soil from spring to early autumn, when the adult beetles are laying their eggs. Check the directions before using on edible crops.

• Biological control - Another eco friendly method of control is to use nematodes. These microscopic worms are parasites which can be bought and watered into the soil between March and October. They will not damage the plants, but will infect the larvae with a disease which will kill them. It can be difficult to ensure the conditions are entirely right to use a pathogenic nematode successfully.

If you have any questions about Vine Weevil or have a question about anything above, please comment below or contact me.