Vine weevils

In short

The vine weevil is a beetle whose adults notch leaf edges at night and whose grubs eat roots, tubers and stem bases in the soil. The grubs are especially damaging to plants in containers, which can suddenly wilt and die with most of their roots gone.

How it looks

Adults are dull black, pear-shaped weevils about 9 mm long with a short snout, elbowed antennae and small dirty-yellow flecks on the wing cases. They cannot fly, move slowly and feed at night, hiding by day under pots, debris and in the leaf litter. All adults are female and reproduce without mating. Grubs are plump, creamy-white, legless and C-shaped, up to about 10 mm long, with a pale brown head; they are found among roots in the potting mix.

Signs

Irregular U-shaped notches chewed into leaf margins (adults). Plants that wilt and collapse even though the mix is moist, with roots eaten away and grubs visible when the plant is tipped out; tubers of cyclamen and begonia bored into.

Life cycle

Adults feed and lay several hundred eggs in the soil or potting mix through spring and summer. Grubs feed on roots from summer through to the following spring, when they pupate in the soil. In the UK the heaviest plant losses occur from about September to March.

What favours it

Plants in containers, where roots are confined; sheltered places such as greenhouses and patios where adults can hide under pots and staging. The species is native to Europe and is also common in North America.

Prevention

• Check leaves for notching and search for adults at night with a torch.
• Inspect roots of bought plants and discard mix containing grubs.
• Put sticky barriers around pots and on greenhouse staging legs.
• Encourage birds, frogs and ground beetles.

Treatment

Start with the first step and move down only if the problem persists.

1. Hand-pick adults at night and destroy them; tip out wilting pots and remove grubs from the roots, repot in fresh mix.
2. Drench pots with insect-parasitic nematodes when grubs are young (RHS: late summer): Steinernema kraussei works in cooler mix (about 5–20 °C), Heterorhabditis species at about 12–20 °C. Nematodes work best in open, moist potting mixes.
3. If still needed, insecticide drenches labelled for vine weevil larvae — follow the product label.

Pros and cons

Look-alikes

Cutworms

Caterpillars with legs and prolegs that cut stems at soil level, rather than legless grubs eating roots.

Root rot

Roots brown, mushy and smelly, but no grubs and no chewed roots.

Affected plants

Many container and garden plants, including rhododendrons, camellias, hydrangeas, hostas, cyclamen, begonias, strawberries and evergreen euonymus.

Related

• Cutworms
• Root rot
• Beneficial nematodes
• Ground beetles
• Quarantining new plants

Sources

1. Vine weevil — RHS
2. Otiorhynchus sulcatus — Wikipedia

Written in our own words from these sources. Check a product label before using any treatment.