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Pest Watch

Vine weevil control

 

Vine weevil is a garden plant pest problem that can be difficult to control. Gardeners with vine weevil will need to take measures to control them.

Vine weevil is one plant insect pest that most gardeners live in fear of. And it is a pest to worry about. Suddenly, otherwise healthy-looking plants collapse and die thanks to the root-eating, soil-borne grubs.

You should suspect a vine weevil attack if watering does not revive the plant. In severe cases, plants may be completely severed from their roots at ground level.

In the past, their favourite food was fuchsias, cyclamen, begonias and primulas. But in recent years they have become less fussy and will make a meal of a much wider range of plants - especially any that are growing in containers. This is possibly due to the use of peat-based and peat-free composts - being less gritty than John Innes composts, the adults are more likely to lay their eggs in them.

What to do if you notice a vine weevil attack?

Don't despair, there are several ways of dealing with this plant-nibbling nasty. It is important to be vigilant and keep a close eye on all your plants - especially those that are known to be favourites on the menu.

Always check the rootballs for grubs before you buy plants. Check when potting up or repotting plants, and destroy any that you see; it usually pays to dispose of affected compost too.

Because vine weevil is such a destructive pest, every effort must be taken to control both the adults and the soil-borne grubs.

There are three ways of controlling vine weevil: chemical, biological control and physical barriers.

Controlling vine weevil grubs

The C-shaped vine weevil grubs

Typical vine weevil grubs, which will eat the roots of a wide range of different plants.

They are creamy-white, up to 13mm (0.5in) long, C-shaped, with a brown head and no legs.

Often the first signs of damage are only spotted when a plant completely wilts and dies.

Commercial nurseries may sometimes add chemicals to the compost to control them. It is always worth asking when you are buying particularly susceptible plants if any such chemicals have been used.

There are a number of insecticides that can be used to treat plants and give protection against attack. Bayer Garden Provado Vine Weevil Killer 2* and Scotts BugClear Ultra Vine Weevil Killer are systemic insecticides that can be used for any container-grown plants (apart from edible ones); they are watered onto the compost.

Bayer Garden Provado Ultimate Bug Killer* and Scotts BugClear Ultra are also systemic and are sprayed onto plant foliage to kill leaf pests, but may also give some control of vine weevil grubs (some edible plants can be treated; check the label first).

Use plant protection products safely. Always read the label and product information before use.

If you don't like using pesticides, use a biological control based on nematodes. These microscopic creatures enter the bodies of the grubs and release a specific bacteria that poisons and kills them. They then multiply and go on to attack other grubs. The nematodes are available from several mail order supplies, such as Defenders, Scarletts PlantCare, Just Green and Green Gardener. See the suppliers list for details.

* In 2016, Bayer Garden changed the active ingredient in Provado Ultimate Bug Killer to one that doesn't have a systemic action. The company also stopped selling Provado Vine Weevil Killer 2.

Controlling vine weevil beetles

Signs of typical vine weevil beetle damage to a rhododendron leaf

Typical vine weevil beetle damage to rhododendron leaves...

Vine weevil adult

..and a typical vine weevil adult beetle.

One of the most effective - but time-consuming - methods of controlling the adult vine weevil beetles is to check your plants at night when they are active and feeding. They can then be scooped up and disposed of.

Another way is to use a physical barrier as the adult beetles cannot fly from plant to plant. Stand potted plants on upturned pots sat in saucers of water - the adults can't swim. Or surround the pots with Barrier Glue available from Agralan - the adults cannot walk across it. With either of these methods it is important to move plants away from walls or greenhouse/conservatory walls as the adults can jump down onto them; they cannot fly.

Physical barriers on top of the soil or compost also work very well. Add a 2cm (0.75in) deep layer of sharp grit or gritty gravel on top of the compost or around the base of the plant to prevent the adults from laying eggs; the egg-laying structure is irritated by the scratchy feel.

Vine weevil eggs

All vine weevil adults are female, and each one can lay hundreds to thousands of eggs from April to September; the main egg-laying periods are April and August/September.

If you spot golden-brown or clear egg-like objects in the soil or compost then they're NOT vine weevil eggs. Vine weevil eggs are brown and tiny and you'd need a hand lens to see them. Clear spheres are usually slug or snail eggs and the golden-brown ones are actually controlled-release fertiliser!

Suppliers

Buy a range of pest control products, inluding biological controls, from my affiliate companies, Harrod Horticultural and Greenfingers.com

 

If you want to know more, or if you've got a gardening problem you need help with, then send an e-mail to: info@gardenforumhorticulture.co.uk

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