GARDENING: Vine weevil grubs are like Doctor Who giant maggots

HORROR SHOW: The unpleasant root�eating grubs. Below, an adult vine weevil.
HORROR SHOW: The unpleasant root�eating grubs. Below, an adult vine weevil.

I HATE vine weevils. They’re underhand and sneaky. Luckily, I’ve avoided any major attack until now.

My experience has been in my mam’s back garden, which is full of container­-grown plants ­- the perfect hunting ground for adults to lay their eggs (they like the non­gritty compost).

All her strawberries were killed a couple of years ago.

The adults are bad enough, but it’s the grubs that really get me. They look like the giant maggots in the 1973 Dr Who episode The Green Death.

Creamy, fat, C­shaped legless grubs have light brown heads and are up to 10mm (about 3/8in) long.

During autumn and winter, they feed on plant roots, causing wilting, and often plant death.

One of my new Heuchera Silver Blush simply came away in my hand as I was weeding round it ­roots severed, with a couple of grubs underneath.

Plants grown in open ground are less susceptible, although the grubs can kill strawberries, Primula, Polyanthus, Sedum, Heuchera and young yew plants.

The adult beetles feed on the foliage of many herbaceous plants and shrubs, especially Rhododendron, evergreen Euonymus, Hydrangea, Epimedium, Bergenia, Primula and strawberry.

They are about 9mm (about 5/16in) long, dull black beetles with a pear­shaped body when viewed from above.

All adults are female and each can lay many hundreds of eggs from April to September. The eggs are brown and less than 1mm (about 1/16in) in diameter, making them very difficult to see.

Larger yellowish­-brown spherical objects seen in potting composts are likely to be controlled-release fertiliser pellets ­- similar whitish objects are usually slug/snail eggs.

Organic Control

1. On mild spring or summer evenings, inspect plants and walls by torchlight and pick off adult weevils. Shake shrubs over an upturned umbrella to collect more. In greenhouses, look under pots or on the underside of staging where the beetles hide during the day.

2. Trap adults with sticky barriers placed around pots or on greenhouse staging.

3. Encourage natural enemies ­ birds, frogs, toads, shrews, hedgehogs and predatory ground beetles.

4. Stand potted plants on upturned pots sat in saucers of water ­ the adults can’t swim.

5. Surround pots with Barrier Glue from Agralan ­ the adults cannot walk across it. Move plants away from walls, as the adults can jump down on to them; they cannot fly.

6. 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.

7. Adult vine weevils hide in debris around the bases of plants so keep the area free from dead and fallen leaves.

8. Place landscape fabric at the base of plants to prevent newly­hatched larvae from entering the soil.

9. A biological control of the larvae is available as a microscopic pathogenic nematode (Steinernema kraussei). Apply in August or early September when the soil temperature is warm enough for the nematode to be effective (5­20oC/41­68oF).

10. Another nematode, Heterorhabditis megidis, is also available but is more temperature-dependent (12­20oC/ 54­68oF). Both nematodes can also be applied to garden soil, but give poor results in dry or heavy soils. They work best in open potting composts, such as peat or coir. Nematodes can be used safely on all edible and ornamental plants.