Vine Weevil
Vine weevils are a classic 'silent' container pest.
Vine Weevil at a glance
| Also known as | Black vine weevil (Otiorhynchus) |
|---|---|
| Affected parts | Leaves (adults), roots (larvae) |
| Most at risk | Container trees of many kinds; a serious hidden root pest (yew, privet, many broadleaf) |
| Main cause | Weevil larvae feeding on roots in the pot |
| Severity | Larvae are very destructive — can kill a tree before you notice |
| Reversible? | If caught before roots are destroyed |
What to look for
- Leaves: Irregular notches bitten out of leaf edges (adult feeding); adults are dull black, slow, flightless beetles ~9 mm, active at night.
- Soil: Creamy-white, legless, C-shaped grubs (~10 mm) with a tan/brown head in the soil and around the roots.
- Roots: Roots eaten away/stripped; the tree may lift loosely in the pot.
- Whole tree: Sudden wilting, poor growth, or collapse despite correct watering — often the first obvious sign, by which point root damage is advanced. Confirm by checking the rootball.
Overview
Vine weevils are a classic 'silent' container pest. The night-feeding adults notch leaf edges (mostly cosmetic), but the real danger is below ground: their fat, white, C-shaped, brown-headed grubs devour roots inside the pot, and a tree can be hollowed out at the roots and collapse before the owner realises anything is wrong.
Causes
Adults laying eggs in container soil through summer; grubs then feeding on roots into autumn/winter; introduction on infested nursery plants.
Commonly confused with
Caterpillars/sawflies also chew leaves but from the surface, not neat edge-notches. Drought and root rot also wilt/collapse a tree — but here you find grubs and chewed roots. Always check the rootball when a healthy tree declines for no clear reason.
Which species are affected
Very wide host range in containers; notably damaging to yew, privet, and many broadleaf species; any potted bonsai is at risk.
Treatment
Check the rootball — pick out and destroy all grubs; repot into fresh soil, washing the roots. Drench the soil with an appropriate weevil insecticide, or apply pathogenic nematodes (Steinernema kraussei / Heterorhabditis) when soil is warm enough. Pick off adults at night. Repeat inspections.
Prevention
Inspect roots at every repot; quarantine and check new plants; apply nematodes preventively in late summer where weevils are known; trap adults; keep pots off the ground where practical.