How to identify and deal with Vine weevil

Vine weevil

Otiorhynchus sulcatus

Adults notch leaf edges at night; their plump C-shaped grubs devour roots, especially in containers. Hand-pick adults after dark and water in biological nematodes in late summer.

Insect Root feeder Ruinous SpringSummerAutumnWinter

How to know it

The adult is a dull black weevil about 9 mm long with a short broad snout and faint yellow flecks, flightless and strictly nocturnal. The grub is the real problem: a plump, legless, creamy-white C with a tan head, found curled among the roots when a pot is knocked out.

What you'll see

Neat semicircular notches bitten out of leaf margins, most obvious on heuchera, euonymus, bergenia and rhododendron.
A container plant that wilts and collapses in autumn or spring with no obvious cause.
A plant that lifts straight out of its pot because the roots below have gone.
Fat white C-shaped grubs with tan heads among the compost when the rootball is broken open.
Primulas, cyclamen, strawberries and heucheras dying one by one through the winter.

Where it comes from

Almost all adults are female and each lays several hundred eggs from midsummer, without needing to mate. The grubs feed on roots through autumn and winter — the season when the damage is done and nobody is looking — pupate in spring, and the new adults emerge to notch leaves from May. Adults live for a year or more and cannot fly, so they walk in, or arrive in a bought pot.

Container plants above all: peat-based compost, a soil-less environment and no predators is exactly what the grubs want. Open ground is far less affected, but strawberries, primulas and cyclamen suffer there too.

Dealing with it

Water in Steinernema kraussei nematodes in late summer or early autumn while the grubs are small and the compost is above 5 °C — this is the one control that reliably works.
Repeat the nematode drench in spring on pots that were badly affected.
Go out after dark with a torch and pick the adults off the foliage; they drop, so cup a hand beneath.
Knock out and check the rootball of any suspicious pot, and pick the grubs out by hand.
Bin infested compost rather than tipping it on the garden or reusing it.

Keeping it out

Check the compost of every bought container plant — this is how vine weevil arrives in most gardens.
Stand vulnerable pots on gravel or a bench, and use tight-fitting mulch mats or grit over the compost.
Grease-band the legs of staging and the rims of prized pots; the adults cannot fly and must walk.
Treat with nematodes annually as routine on heucheras, primulas, cyclamen and strawberries in pots.
Encourage ground beetles, frogs and birds, all of which take adults on open ground.

What it goes for

Roots & tubersLeavesBulbs & corms

Anything in a pot, but heucheras, primulas, cyclamen, begonias, fuchsias, strawberries, sedums and young shrubs are the classics.

and 43 more in the catalog

Who hunts it for you

Beneficial nematodesSteinernema & Heterorhabditis spp. Microscopic worms watered onto damp soil that hunt down soil-dwelling grubs and release a bacterium that kills them within days. Timing is the whole thing: warm, damp soil and a small target grub, which means late summer for most of what they are used against.
Frogs & toadsAnura A resident toad works the beds every night for slugs, cutworms, and weevils. Recruit them with water — even a sunken basin pond — plus damp shade and an upturned-pot toad house; skip the slug pellets that poison their prey.
Ground beetleCarabidae Fast, glossy night hunters that patrol the soil surface for slugs, cutworms, and root-fly larvae. Give them daytime cover — thick perennial edges, stepping stones, a log — and skip the tillage that wrecks their burrows. Grow to recruit it: Lavender,Mint,Thyme
HedgehogErinaceus europaeus A European animal, and worth saying so plainly: there are no hedgehogs in North America, and the ally that does the same night shift here is the toad, the opossum or the ground beetle. Where they do occur, cut a gap in the fence and skip the pellets.