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June: Vine Weevil

One of the most destructive pests found in many gardens today is the invisible vine weevil. The adult emerges from its daytime hiding place to feed on leaves and to lay eggs at the base of the plant. The developing grubs munch away at the roots. The first signs of any damage are when the plant begins to wilt even though the soil is moist. And then it is almost sure to be too late to save it.

Plants grown in containers are particularly susceptible to attack because they are growing in close proximity to each other and this gives excellent protection from predators. Plants growing in pots or other containers, in the open or under cover, can be severely affected by vine weevil grubs. In open ground damage is less likely although the grubs sometimes cause damage, particularly to strawberries, primulas, polyanthus, sedum, heuchera and fuchsias. The adult beetles feed on the foliage of many herbaceous plants and shrubs especially rhododendron, evergreen euonymus, hydrangea and bergenia.

Irregular-shaped notches are eaten in leaf margins by the adult weevil during the summer. Plants wilt and die during autumn to spring as a result of grubs devouring the roots.

Adult vine weevils are responsible for the leaf damage that can be unsightly but rarely affects the plant's growth. The adults are 9mm long, dull black beetles with a pearshaped body when viewed from above. They are slow moving insects that cannot fly but they are very persistent crawlers and climbers.

Far more serious is the damage caused by the soil-dwelling larvae that are plump, white, legless grubs up to 1cm (0.5") long with pale brown heads. These feed on roots and also bore into tubers and succulent stem bases devastating many herbaceous plants. They also kill woody plants by gnawing away the outer tissues of the larger roots and stem bases.

Non-Chemical control

On mild spring or summer evenings inspect plants and walls by torchlight and pick off the adult weevils. Shake shrubs over an upturned umbrella to dislodge and collect more. In glasshouses, look under pots or on the underside of staging where the beetles hide during the day. Trap adults with sticky Tree Grease bands around pots or glasshouse staging. Encourage natural enemies. Vine weevils and their grubs are eaten by a variety of predators such as birds, frogs, toads, shrews, hedgehogs and predatory ground beetles.

When potting established plants such as shrubs into containers a liquid drench of Provada Vine Weevil Killer to the root ball before planting is recommended. Repeating the drench to the container every four months. These products also give excellent control of aphids such as green, white and black fly but note they can only be used on ornamental plants, NOT on plants that are to be consumed. It is important to recognise the signs of vine weevil damage as stopping treatment after the apparent disappearance of the pest can allow numbers to build up again.