Lily beetle

Be on the look out for Lily beetle on prized blooms from June onwards, says Plant Doctor Helen Derrin

I would forgive the beautiful lily beetle almost anything apart from eating my lilies! Despite my best efforts, they seem to return year after year at this time to munch irregular holes in leaves, flowers and anything else they can find called lily – actually they limit themselves to the true lilies (lilium) and fritilaries. If the attack is severe, plants can be destroyed. Ten years ago they were considered a pest of the Home Counties, but now they have spread out far and wide.

What to look for

They are the easiest adult pest to recognise in the garden because they’re pillar-box red, about the size of my little fingernail (6-8mm) with black heads. They literally shine out from the pale green leaves, flowers and seedpods they are happily destroying. The orange, black-headed grubs are not nearly so loveable – appearing on the plants from mid-summer – often looking like dirty slugs because they cover themselves with their own excrement – yuck! The scarlet adult and slimy grub are active throughout the summer, so they have plenty of time to cause maximum damage.

Lifecycle

Adults overwinter in leaf litter to emerge in early spring when they mate and lay small clusters of brown eggs on the undersides of leaves. Each female can lay a couple of hundred eggs. These hatch about a week later when the larvae emerge to feed voraciously for a further three or four weeks. They then pupate in the soil, to emerge as adults after less than a month. Up to three generations can occur each year.

Control

Despite being easy to see and recognise, lily beetles are very hard to control. I’ve done my best picking off adults and destroying them, but the grubs are more illusive. Unfortunately, chemicals need to be sprayed directly onto them and even this has limited success in my experience. Use an insecticide containing the active ingredients bifenthrin, pirimiphos-methyl or permethrin. Good luck!