The vine weevils is an insect that can cause serious damage to a wide range of ornamental plants and fruits, especially those grown in containers.
Very common in UK gardens and highly destructive, adult weevils eat plant leaves during spring and summer, but it is their grubs that cause the most damage. Feeding on the roots of plants during autumn and winter, an infestation often results in plant death.
Here’s everything you need to know about the pernicious little bug, and how you can prevent it from wreaking havoc in your garden.
How do I recognise a vine weevil?
Adult vine weevils are usually about 9-10mm long, with a black body with yellow flecks that looks pear-shaped when viewed from above. As they hide in the dark during the day, you’re more likely to spot them on your plants at night – they can’t fly, and are slow-moving crawlers.
All adult vine weevils are female and each can lay several hundred eggs during spring and summer. As they are even more damaging to plants, it’s very important to keep an eye out for vine weevil larvae, which are c-shaped, legless and white, up to a centimetre long, with pale brown heads.
How do vine weevils affect the plants in my garden?
Adult vine weevils bite notches into plant leaves and vegetation, which looks unpleasant but rarely affects plant growth. Far more serious is the damage caused by the soil-dwelling grubs; these will eat the roots of a wide range of plants, and can bore into tubers and stem bases. They will cause plants to wilt and die if left unchecked; most plant damage is caused from September to March as the grubs grow to adulthood.
Plants growing in pots and containers, outdoors or under cover, are most likely to be by vine weevil grubs - cacti, succulents, cyclamen, begonia and heuchera are particularly at risk. Plants growing in the open ground are less likely to be damaged, though it is best to check carefully.
How do I control vine weevils?
In spring and summer, the Royal Horticultural Society recommends inspecting plants and walls by torchlight and picking off adult weevils. They suggest shaking shrubs over newspaper to dislodge and collect more. They can also be trapped using sticky barriers placed around pots.
In sheds and greenhouses, look under the base or lip of pots and under benches; vine weevils also love to conceal themselves under debris, so pick up fallen leaves and sweep up in the greenhouse to reduce the number of hiding places.
Ornamental plants grown in containers can be treated by drenching their compost with dedicated weevil-killing insecticides, which are widely available. Use in mid-to-late summer will control larvae for up to four months. Remember, though, that these can’t be used to treat edible plants or ornamental plants growing in the ground.
If you don’t want to use chemicals, there are also biological weevil killers available that contain nematodes - microscopic creatures that are a natural enemy of vine weevils – which can be used in containers and in the open ground. These should be applied in August and early September, but they do work best in lighter soil, peat and compost.
It’s also important to keep checking your plants, even after using weevil killers; stopping control measures can allow vine weevils to reappear.