Non chemical control
Where only a few lilies and fritillaries are being grown, the plants should be regularly inspected from late March onwards so that adult beetles, larvae and eggs can be removed by hand.
For extensive infestations, it may be necessary to use an insecticide, such as thiacloprid (e.g. Bayer Provado Ultimate Bug Killer), acetamiprid (e.g. Bug Clear Ultra), deltamethrin(e.g. Bayer Sprayday Greenfly Killer, Bayer Provado Ultimate Fruit & Vegetable Bug Killer) or lambda- cyhalothrin (e.g. Westland Resolva Bug Killer). Organic gardeners can use pyrethrum (e.g. Py Spray Garden Insect Killer, Doff All in One Bug Spray, Bug Clear Gun for Fruit & Veg, Pyrol Bug & Larvae Killer or Growing Success Fruit & Veg Bug Killer). Pyrethrum should control newly hatched larvae but will be less successful against the adult beetles.
Plants in flower should not be sprayed to avoid harming bees and other pollinating insects.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)