How do I deal with vine weevil?

Vine weevil does its real damage out of sight. By the time a plant shows it, the grubs have usually eaten the roots away completely.

Safety

Step by step

1. Recognise the adult damage.Neat semicircular notches bitten from the edges of leaves, especially on heuchera, bergenia, euonymus, rhododendron and primula. Distinctive and largely cosmetic.
2. Recognise the serious symptom.A container plant that wilts despite moist compost, then dies quickly. Lift it — if it comes away with almost no roots, grubs have eaten them.
3. Know what you are looking for.Grubs are creamy white, about a centimetre long, C-shaped, with a distinct brown head and no legs. Legs mean it is something else and probably harmless.
4. Check the compost of any suspect pot.Tip it out onto a sheet and go through it. Grubs are usually clustered around the rootball, and finding them settles the diagnosis immediately.
5. Understand why containers suffer most.Peat-free and soilless composts suit the grubs, and pots lack the ground beetles and birds that eat them in open soil. Vine weevil is overwhelmingly a container problem.
6. Use nematodes as the main control.Steinernema kraussei or Heterorhabditis, watered into moist compost. Late summer to early autumn is the key window, when grubs are small and soil is still warm.
7. Follow the nematode conditions exactly.Soil above about 5°C, compost moist before and after, applied before the use-by date, and kept refrigerated until use. Most failures are one of these four rather than the product.
8. Repot a badly affected plant.Wash all the old compost off the roots, kill every grub you find, and repot into fresh compost. It is the fastest way to save something valuable.
9. Hunt the adults after dark.They are nocturnal, flightless and all female. A torch after dusk, and shaking foliage over a sheet, collects them. Every adult removed prevents several hundred eggs.
10. Use a physical barrier on pots.Grit or gravel over the compost surface makes egg-laying harder. A band of horticultural glue around a pot stops flightless adults climbing in.
11. Encourage predators.Ground beetles, birds, frogs and hedgehogs all eat them. Log piles, gaps under fences and less tidiness at ground level all help in open borders.
12. Check new plants before they join the collection.Vine weevil arrives most often in a bought plant's compost. Inspecting the rootball of anything new is worth the two minutes.
13. Treat the whole group of pots.Adults walk between containers, so treating only the affected one leaves the population intact next door.
14. Repeat annually where it recurs.One treatment reduces the population rather than eradicating it. An autumn nematode application each year keeps it under control.

Tips

• Notched leaves are cosmetic. A wilting pot plant with no roots is the emergency.
• Nematodes in late summer, into moist compost, is the treatment that actually works.
• Grubs are legless with a brown head. Anything with legs is not vine weevil.

Common mistakes

• Treating only the leaf damage — The adults chewing leaves do little real harm. The grubs eating roots below the surface are what kill plants, and they need treating separately.
• Applying nematodes to dry or cold compost — They are living organisms that need moisture to move and warmth to be active. Applied to dry or cold soil they die without reaching the grubs, and the treatment appears to have failed.

If it doesn't work

Questions people ask