(Otiorhynchus sulcatus) Vine weevils are beetles that attack a wide range of plants. The adults eat the leaves, but the more devastating grubs, or larvae, eat the roots and kill plants.
- Dark brown or black beetles with yellow markings found on leaves and flowers
- Creamy-white, C-shaped, legless grubs with brown heads in soil or compost
- Characteristic “mouth-shaped” notches on the edges of leaves
- Plants suddenly wilt, even when watered, and may die
What are vine weevils?
Vine weevil is a type of beetle. Both the adult beetle and the larvae attack plants.
The adult beetles measure around 9-10mm (5/16in) long and are a dull black colour with yellow markings. Being a weevil, they have a proboscis or snout, bearing their antennae. They can be found walking over the leaves of plants, on the ground, on walls and even in the home or greenhouse. They cannot fly.
The creamy-white, C-shaped, legless larvae have a brown head and are roughly the same size. They can be found in the soil or compost, usually close to plant roots. You may also find them in begonia tubers.
All vine weevil adults are female, and each one can lay up to 1,00 eggs per year from April to September; the main egg-laying periods are April and August/September.
What do they affect?
- Bulbs, tubers and corms
- Herbaceous perennials
What do they do?
The adult beetles feed on the leaves of many different plants, but especially bergenia, epimedium, hydrangea, primula and rhododendron, producing characteristic “mouth-shaped” notches on the margins of leaves, but do very little damage.
The larvae, on the other hand, can cause severe damage. They feed on plant roots, preventing the plant taking up water. Plants start to wilt and continue wilting, even when thoroughly watered. In severe cases, plants may be completely severed from their roots at ground level, causing them to wilt and die.
The larvae will also feed on large root-like food storage organs – begonia tubers are a favourite food.
Despite their name, vine weevils don’t only feed on vines, they will attack a wide range of plants. In the past, their favourite food was begonias, cyclamen, fuchsias, primulas and sedums. But now they are much less fussy and will make a meal of a much wider range of plants, both indoors and outside, especially any that are growing in containers.
How to control vine weevils
Inspect plants regularly for signs of the adult beetles and pick off and destroy any you see. They are mainly nocturnal, so you’ll have to go out at night with a torch. You could shake plants over an upturned umbrella to dislodge and collect them. Look under pots, including in the greenhouse, as this is often where the beetles hide during the day.
Check plant rootballs for grubs whenever repotting, potting up or buying plants, and destroy any that you see. It is also worth disposing of affected compost too, since there may be eggs (which are small, brown and more-or-less invisible to the naked eye) in the compost.
Clear or golden-brown egg-like objects in the soil or compost are not vine weevil eggs. Clear spheres are probably slug or snail eggs, and the golden-brown ones are controlled-release fertiliser!
Both vine weevil adults and grubs have numerous natural predators – including birds, frogs, ground beetles, hedgehogs and toads – so do what you can to encourage these into your garden.
There are biological controls for vine weevil larvae, based on nematodes, these are watered onto the compost or soil. The best times to apply them are April and August/September.
A trap containing nematodes is also available from Green Gardener for controlling adult vine weevil.
As the adult beetles cannot fly from plant to plant, physical barriers may help prevent them getting to your plants. Stand potted plants on upturned pots or a brick sat in saucers full of water, as the adults can’t swim. Or surround the pots with Barrier Glue, since they cannot walk across it. With either of these methods it is important to move plants away from walls or greenhouse/conservatory walls, as the adults can jump down onto them.
Contact insecticides are unlikely to give any control of the adult beetles, but a systemic insecticide, which is absorbed by the leaves and moves all around inside the plant, should be effective when the beetles eat the leaves.
BugClear Ultra Vine Weevil Killer is a systemic liquid drench watered on to the compost of container-grown plants. It should kill the grubs and give protection from further attack for up three or four months. This is not approved for use on edible plants or plants growing in the ground.
Use plant protection products safely. Always read the label and product information before use. Plants in flower should not be sprayed due to the danger to pollinating insects. Either spray early in the morning or late in the evening when pollinating insects are less likely to be active.
Not all insecticides have approval for use on all edible crops. Check the label before spraying.
Physical barriers placed on top of the soil or compost should prevent the adult beetles laying eggs, and so stopping the larvae in the first place. A 2-2.5cm (¾-1in) deep layer of sharp grit or gritty gravel placed on top of the soil or compost around the base of the plant usually works well; the beetle’s egg-laying device is irritated by the scratchy feel.
- Contact insecticides
- Systemic insecticides