Lily beetle

Lily beetle – sometimes referred to as scarlet lily beetle or red lily beetle – is the most serious pest of lilies (Lilium), fritillaries (Fritillaria) and tree lilies (Cardiocrinum). It can reduce a lily plant to just about nothing in a few days.

The adult beetle is about 5-8mm (about ¼in) long, an attractive looking bright red with a black head and legs. They lay eggs on the underside of leaves in groups of up to 12-15; these can vary in colour from bright orange to nearly red.

The larvae that hatch from these eggs have dirty orangey bodies and cover themselves with their own excreta; this gives them some protection from predators and they can be mistaken for birds’ droppings. After feeding, they fall onto the ground and pupate, turning into adult beetles.

Adult beetles emerge from the soil from late March to May, laying eggs from April until September. They overwinter in sheltered places, often in the soil but not always near lilies.

Once restricted to certain parts of the UK, mainly the South-East, lily beetle is now more widespread over much of the UK.

• Lilies (Lilium)
• Fritillaries (Fritillaria)
• Tree lilies (Cardiocrinum)
• Adult beetles are sometimes found on other plants

Both the adult lily beetle and the horrible grubs (larvae) have a voracious appetite and devour lily leaves, stems, flowers and flower buds.

Apart from spoiling the plants’ appearance, and reducing the number of flowers produced, severe attacks can weaken the bulbs, which may not flower the following year.

You can easily control a small numbers of lily beetles. Check plants regularly from March onwards, and deal with any you see.

Slowly and carefully approach the plants, and pick off and kill any adults or grubs as soon as they’re seen. This is best carried out early in the morning when the adults are sluggish and easy to catch. If disturbed, they will drop to the ground on their backs where they can be difficult to see. Use gloves for the larvae. The eggs can be squashed on the leaves – or remove the leaf containing either larvae or eggs and destroy it.

There are numerous chemical insecticides available that will kill soft-bodied insect pests, such as lily beetle larvae. Just bear in mind that the majority of these are what is known as “contact” insecticides. That is, you have to spray the actual insect (make contact with it) to kill it. If you miss some, or others land on the plant after spraying, these will not be affected. Also, most are based on “organic” or “naturally-occurring” materials and have very little persistence once sprayed on to the plant. This means you have to spray regularly – which could be as often as every couple of days in a warm summer.

A systemic insecticide which also kills on contact – is absorbed by the leaves and moves all around inside the plant, so can control future attacks for up to two months.

Use plant protection products safely. Always read the label and product information before use. Plants in flower should not be sprayed due to the danger to pollinating insects. Either spray early in the morning or late in the evening when pollinating insects are less likely to be active.

There is very little you can do to prevent lily beetles attacking your plants. But don’t grow lots together, since the concentrated smell will attract the beetles, but even isolated lily plants can be attacked.

Research has shown that Asiatic lilies are the most vulnerable, while some Oriental lilies are more resistant to attack. The variety ‘Defender Pink’ shows resistance to lily beetle in trials.

• Contact insecticides
• Systemic insecticides