Plants growing in pots or other containers, out of doors or under cover, can be severely affected by vine weevil grubs. Plants growing in the open ground are less likely to be damaged, although the grubs will sometimes kill Strawberries, Primulas, 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, Epidmedium, Bergenia, Primula and Strawberry. Irregular-shaped notches are eaten in leaf margins by the adult weevils during the summer. Plants wilt and die during Autumn to Spring as a result of grubs consuming the roots. The serious damage is caused by the soil-dwelling larvae which are plump, white, legless grubs up to 1cm (0.5in) long with pale brown heads, feeding on roots and boring into tubers and succulent stem bases, ruining many herbaceous pot plants. They can also kill woody plants by gnawing away the outer tissues of the larger roots and stem bases.
The two main methods for control are:
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 barriers, such as Agralan Insect Barrier Glue, around pots or glasshouse staging.
Vine weevils and their grubs are eaten by a variety of predators such as birds, frogs, toads’ shrews, hedgehogs and predatory ground beetles, so encourage natural enemies. A biological control of the larvae is available as a microscopic pathogenic nematode available from biological control suppliers. Apply in August or early September when the soil temperature is warm enough for the nematode to be effective. 5-20OC (41-68OF) and before the vine weevil grubs have grown large enough to cause damage.
Applying a liquid drench such as Provado Vine Weevil Killer 2 is a better option for established plants. This insecticide gives protection against the grubs for up to four months, but treatment in mid to late summer will control the young larvae and prevent damage occurring later in the Autumn to Spring period.
Gardeners with vine weevil should be vigilant, because stopping treatment after the apparent disappearance of the pest can allow numbers to quickly build up again.
Remember to use chemicals safely and always read the label before use.
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