Could Vine Weevil Grubs Be Eating My Rhubarb Roots?

Vine weevil (Otiorhynchus sulcatus) is a widespread garden pest whose C-shaped cream grubs feed on the roots of a wide range of plants. While rhubarb is not the most common victim — vine weevils often prefer container-grown plants and softer-rooted species — established rhubarb in gardens with high vine weevil pressure can be affected, particularly when grubs are numerous enough to attack the coarser roots. A plant that wilts inexplicably and is loose in the soil — when you tug it — with roots chewed off near the crown is a classic vine weevil signature.

Identifying vine weevil damage

Dig around a suspect plant and examine the soil and root zone. Vine weevil grubs are plump, C-shaped, creamy-white with a brown head capsule — up to 1cm long when fully grown. They feed from late summer through winter and into spring, typically with the worst damage in autumn and early winter. Adult weevils leave characteristic notched U-shaped bites around the margins of leaves (visible in spring and early summer) which can confirm their presence in the garden before root damage becomes apparent.

Biological control with nematodes

Steinernema kraussei (a parasitic nematode) is the most effective organic control for vine weevil grubs. Apply in late summer (August–September) or early autumn to warm, moist soil — this is when the young grubs are small and most susceptible. The nematodes seek out and kill grubs in the soil. Treatment needs to be repeated in subsequent years as it does not provide permanent control. Ensure soil temperature is above 5°C and the soil is moist at application.