At peak lavender time when the plants are in full leaf and flower, you may find a particularly attractive beetle on the plant foliage. Commonly (but confusingly) called the rosemary beetle (Chrysolina americana), probably because it affects rosemary plants too, this psychedelic shiny, stripy purple and green metallic like beetle has iridescent armour covering its small body. It’s about 7-8 mm long and an illegal immigrant from Europe and eats the foliage of a range of aromatic plants such as rosemary, lavender, sage and thyme. It’s stripy larvae are also fairly destructive, feeding on foliage and flowers.
Controlling rosemary beetle
The beetle was first found in the UK in and around London but is now pretty widespread across the whole of the UK. While affected plants can look worse for wear with shredded foliage they are unlikely to die and will recover. Beetles can be dislodged by shaking the plants over newspaper to collect the fallen bugs or by collecting manually. Think carefully before applying a pesticide. Insect killers are not selective and will kill many types of insects including beneficial ones. The host plants are invariably edible herbs and unless you want to add pesticide dressing to the menu, poisonous sprays are best avoided. Prune out damaged growth, pick off the beetles and give your plants a restorative feed to help them recover.