Strawberry root weevil
Otiorhynchus ovatus & Anthonomus signatus
also called Black vine weevil relatives, Strawberry clipper
Notched leaf edges above ground and grubs eating the crown below it — and a separate small weevil, the clipper, that snips the flower buds clean off.
How to know it
The root weevil is a small black weevil 5 mm long with a short snout, flightless, and active at night; the grubs are legless white C-shaped larvae with a tan head, in the soil at the crown. The strawberry clipper is a smaller reddish-brown weevil with a long curved snout, and identifies itself by the damage: flower buds cut through at the stalk and left hanging or dropped.
What you'll see
- Neat semicircular notches chewed into the edges of leaves, as if punched with a hole punch.
- Plants wilting and dying in patches, with the crown eaten away when lifted.
- Legless white grubs in the soil around the crown and roots.
- Flower buds hanging by a thread or lying on the ground, cut cleanly at the stalk — the clipper.
- Weevils indoors in late summer, since the root weevil is a notorious accidental house invader.
Where it comes from
Root weevils are all female and reproduce without mating, laying in the soil in summer. The grubs feed on roots and crowns through autumn and spring, which is when the plants die, and adults emerge in early summer to notch the leaves. The clipper is separate: it overwinters in leaf litter and woodland edges and cuts buds for a few weeks in spring only.
Strawberry beds in their second and third years, and gardens next to woodland for the clipper. Well-mulched, undisturbed beds favor the root weevil grubs.
Dealing with it
- Water in parasitic nematodes (Heterorhabditis or Steinernema) in late summer or early autumn while the grubs are small and the soil is warm and damp.
- Renovate and replant the strawberry bed on fresh ground rather than nursing a badly infested one.
- Trap adults at night under boards or rolled corrugated card laid in the bed and clear them each morning.
- Cover with mesh through the clipper flight in spring if bud clipping is severe.
- Take the notched leaves as a warning to treat for grubs in autumn, not as damage worth treating itself.
Keeping it out
- Start new beds from certified clean runners on ground that has not grown strawberries.
- Rotate the strawberry bed every three or four years.
- Clear leaf litter and rough growth from the boundary, which is where the clipper overwinters.
- Apply nematodes annually in a garden with a history of it.
- Encourage ground beetles and rove beetles with mulch and undisturbed edges.
What it goes for
Strawberries above all, then raspberries, blueberries, rhododendron, azalea, yew and heuchera.
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.
- 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
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com