Strawberries: Vine weevil grubs on the roots
Question: In the past four or five years my strawberries have died off and when I pull them up I find maggots have been eating the roots. (Mr LP Giles, Stoke Ferry)
The problem with your strawberries is vine weevil, a pest that infests a wide range of ornamental plants and fruits, especially those grown in containers. Adult vine weevils eat leaves, and the grubs eat roots, indoors and outdoors.
It is one of the most common and devastating garden pests. The adult weevils eat plant leaves, but it is the grubs that cause the most damage over autumn and winter when they feed on plant roots.
Plants growing in the open ground are less susceptible, although the grubs can 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, Epimedium, Bergenia, Primula and strawberry.
Adult vine weevils are responsible for the leaf damage, which can be unsightly but rarely affects the plant's growth. The adults are 9mm long, dull black beetles with a pear-shaped body when viewed from above. Far more serious is the damage caused by the soil-dwelling larvae, which are plump, white, legless grubs up to 10mm long with pale brown heads. These eat the roots and also bore into tubers of cyclamen and begonia, and into stem bases of cacti and succulents. They can also kill woody plants by gnawing away the outer tissues. Most plant losses occur during September to March.
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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 greenhouses, look under pots or on the underside of staging benches where the beetles hide during the day. Trap adults with sticky barriers, such as Agralan Insect Barrier Glue, placed around pots or on greenhouse staging.
Encourage natural enemies, and a biological control of the larvae is available as a microscopic pathogenic nematode (Steinernema kraussei) available from suppliers of biological controls.