How do I deal with lily beetle?

Lily beetle has spread across most of the UK since the 1980s and is now the main reason lilies fail in gardens. It is completely manageable by hand if you look regularly, and very difficult to control once a generation of grubs has established.

What you'll need

• A pot or tub of soapy water
• Gloves
• Hand lens (optional)

Step by step

1. Know what you are looking for.Adults are bright scarlet with a black head and legs, about 8mm long, and only on lilies, fritillaries and a few relatives. Nothing else in a UK garden looks like it.
2. Start checking in April.Adults emerge from the soil as soon as the lilies come up. Catching the first arrivals in April prevents the first generation of grubs entirely.
3. Cup your hand underneath before you touch it.Disturbed beetles drop to the ground and land upside down, where their black underside makes them nearly invisible. Catch them from below.
4. Check leaf undersides for eggs.Rows of small orange-red eggs on the underside of leaves. Wiping them off with a thumb is the quickest control there is.
5. Look for the excrement-covered grubs.The larvae cover themselves in a wet black or brown mass of their own droppings, which looks like bird mess on the leaf. Wipe them off with a gloved hand or a cloth.
6. Repeat every few days from April to September.There are overlapping generations through the season. A weekly check is the difference between a few beetles and a stripped plant.
7. Check pots and the surrounding soil.Adults overwinter in soil and leaf litter, often not in the same pot as the lily. Autumn tidying reduces next year's population.
8. Use a systemic insecticide only as a last resort.Where hand picking is not practical, a systemic product labelled for ornamentals works. Do not use it on plants in flower where bees are foraging, and never on edible plants.
9. Grow lilies in pots you can inspect.Pots near the door get checked. Lilies at the back of a border do not, and that is usually where the damage happens.
10. Accept some damage.A few chewed leaves does not stop a lily flowering. The aim is to keep numbers down, not to achieve zero beetles.

Tips

• Cup your hand under the beetle before touching it — they drop and vanish.
• The bird-mess-looking blobs are the grubs, and they do far more damage than the adults.
• Check twice a week from April. Ten seconds a plant is all it takes.

Common mistakes

• Waiting until damage is visible — By then the grubs are established and will strip the plant within a fortnight. The whole method depends on catching the adults in April before they lay.
• Spraying an insecticide over lilies in flower — Lilies are heavily worked by bees and moths. If a spray is genuinely necessary, it goes on before flowering and never on open flowers.

If it doesn't work

Questions people ask