While some beetles, especially ladybirds and various ground beetles, are a gardener’s best friend – as they eat a range of insect pests – others are definitely the opposite. Many adult beetles and their larvae (grubs) attack a wide range of plants. They will eat the leaves and flowers of plants, and some – such as vine weevil grubs – eat the roots.
These are the big 3 plant pest beetles to be on the look out for.
While the adult beetles eat characteristic ‘mouth-shaped’ notches from the edges of many plants, it’s the root-eating, C-shaped, creamy-white grubs that cause the most damage. Affected plants may wilt, no matter how much you water them, and finally die. Adults only tend to come out at night.
The red adult lily beetle may look attractive, but it and its grubs can strip a lily plant of leaves and flower buds in a matter of days. Check the underside of leaves for adults, black/brown grubs and clusters of orange eggs.
Viburnum beetle grubs start attacking viburnums from mid to late spring. They make holes in the leaves, skeletonising them and leaving them look like lace doilies, which gives affected plants a very tattered appearance. Viburnum tinus and Viburnum opulus are most commonly affected.
Other beetle pests of plants include rosemary beetle (also attacks lavender), raspberry beetle, asparagus beetle and flea beetle, which attacks young plants and seedlings – especially those of brassicas.