Vine Weevil

Vine Weevil - Otiorhynchus sulcatus is possibly the most troublesome of the weevils, as their larvae damage the roots of a wide range of pot plants, e.g. Begonia, Cyclamen and Fuchsia.

They have become a more frequent pest in the UK due to containerised plant production and importation.

The adult weevils are matt black with small, yellowish-brown flecks on their wing cases.

Because they are unable to fly (their wings are fused together), they are sometimes mistaken for a form of ground beetle.

Ground beetles are larger, flatter and have a less pointed head.

The adult weevils emerge from the pupa stage in late spring.

They feed on plant material for up to 45 days then they are ready to lay eggs.

Locating and killing adult weevils at this point is a good preventative method of limiting the damage.

They are difficult to control once established, simply because they are nocturnal feeders,and hide in the soil or in plant debris during the day.

Setting traps consisting of rolls of corrugated cardboard that are laid in strategic places for the adults to hide in during the day can help in this process.

Similarly, moist sacking laid on a path provides a dark daytime hiding place for the adults.

In both cases these traps should be inspected daily and any adults found should be disposed off.

Their presence can be recognized by the irregular notching on leaf edges, particularly those nearest to the soil, and on the innermost portions of the plant.

This damage by the adults is not fatal, just unsightly and a good indicator that there will be eggs, and larvae hatching in the autumn.

The real damage will be done by these larvae as they feed on the roots of the plant.

Outdoors, the adults eat the leaves of rhododendrons and other ornamental plants and also damage strawberries and raspberries.

Good garden hygiene may reduce the number of hiding places, and a persistent insecticide, such as BHC, applied as a dust or spray to foliage, soil or potting composts, gives reasonable control.

Adult weevils are all female and each can lay up to 1,500 eggs in a two month period starting from circa Week 27>.

The round eggs are about 1 mm across, and are laid in the soil close to a plant.

They are white at first then turn brown later.

The eggs can often be confused with slow release fertiliser pellets in the soil.

A method of testing is to crush a few of the pellets.

You will find that a fertiliser pellet crushes easier than the relatively hard egg.

The eggs hatch 10 to 12 days later and the creamy-white larvae then burrow down into the root system of the plant/s.

The Larvae:

The larvae are highly destructive.

They feed on roots and bark, and severely damage plants to a point where they often wilt and die.

The first sign of the presence of the larvae is usually yellowing leaves, poor growth and a wilting plant which does not respond to watering.

Unfortunately it is often too late to save the plant.

However, if the symptoms are seen in good time, the plant might be saved by washing off all the compost from the root ball.

This should remove the grubs and remaining eggs from the root system then it only remains to repot the plant into fresh compost.

The legless C-shaped larvae are creamy white with a brown head and grow up to 10mm long.

One generation of pupation occurs in the soil each year.

Control:

Vine weevil can be controlled biologically by treating with nematodes Steinernema kraussei, which are watered into the potting compost.

These remains active for about four weeks at soil temperatures of over 5°C (40 °F)

The treatment is best used between August and November when the weevil eggs are hatching and again from March to May when the soil is warm enough and the larvae are active.

A natural predator is the Centipede which eats both eggs and larvae.

An alternative treatment is to use suitable systemic insecticide.





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