Vine Weevil (Otiorhynchus sulcatus)

What are Vine Weevils?

Vine Weevils are a type of beetle which feed on plants.  They cannot fly but crawl and climb to feed on their chosen leaves.  The adult beetles are around 1cm in length and are a dull black or dark brown colour.

The grub emerges in late Spring and feeds on the host plant for between three and six weeks.  At this point they lay between 500 to 1500 eggs over a period of around a month and take around 1 to 2 weeks to hatch.  A prepupal stage develops late in the year and remains like this until late spring when it pupates fully for a few weeks before the adult finally emerges.  The adults are able to re-produce without a mate.  Whilst the adults are responsible for unsightly chunks being eaten from leaves

Adults can be seen on foliage at night but during the day hide in dark crevices.

Do they harm plants?

Yes.

What damage do they cause?

Damage made by the adult weevils is easier to spot than from their grubs. Notches which are not uniform in shape appear on plant leaves in Summer.


Vine Weevil damage on a holly leaf

Vine Weevil grubs eat plant roots after which the leaves on the plant turn yellow then wilt and the plant eventually dies.

Do they affect any particular plants?

Any plants growing in pots outdoors are particularly at risk, especially young, tender plants. Less likely to be affected are plants growing in the ground.

Adult Weevils feed on many plants, especially the foliage of herbaceous plants and shrubs including Bergenia, Epimedium, Euonymus, Hydrangea and Rhododendron. Grubs feed on many young plants but especially Cyclamen, Heuchera, Polyanthus, Primulas, Sedum, Strawberries and young Yew plants.

How do I get rid of them?

Non-chemical control

Look for adults on spring or summer evenings in the evening with a torch. They have a habit of dropping off a plant when they are disturbed though and their colouring makes them difficult to see on the soil. That said, either take more care than usual or shake the bush over an upturned umbrella or sheet of newspaper. During the day you can find them hiding under pots or in dark corners.

Traps are available for adults which work like a glue barrier trapping the beetle as it crawls up to it's food.

Perhaps the best way to control them is to encourage their natural enemies: birds, frogs, ground beetles, hedgehogs, shrews and toads.

Biological controls are also available to deal with the larvae and grubs which cause the most damage in the form of pathogenic nematodes. Steinernema kraussei needs to applied in August or September as the soil temperature needs to be between 12^oC and 20^oC for the nematode to be effective and before the grubs have caused too much damage. A second nematode, Heterorhabditis megidis is also available but relies more on temperature.  Both can be applied to garden soil but they give best results in damp, less heavy soils like peat.

Chemical control

Some composts available now have the slow release pesticide imidacloprid already mixed in and will control the larvae for up to 12 months.  This is good for potting up hanging baskets, seedlings and cuttings and other 'at risk' plants.

The nematodes described above give perhaps the best option for established plants, but thiacloprid used in liquid form may also be effective.  This is effective for up to 4 months but if the treatment is applied in mid to late summer it will control larvae and therefore prevent damage later in the year and in spring too.

Once the weevils have apparently been controlled, it is a good idea to still keep looking for them as they can re-appear.

Always use chemicals as instructed on the label and wear any gloves etc. when necessary.