The red lily leaf beetle (Lilioceris Ilii) is a destructive pest that feeds almost exclusively on true lilies (Lilium spp.) including Asiatic and Oriental lilies as well as Orienpets and species lilies.
This extremely destructive pest was first discovered in Canada about 50 years ago and has gradually moved south, gradually infiltrating most of New England, Washington, Oregon and now is definitely in central Wisconsin as well. If this pest becomes active in your area, your lilies are at risk.
The lily leaf beetle is oblong, about ¼ inch long and bright, scarlet red, with black legs and antennae. They are easy to see, but they are fast and difficult to catch. If they sense you approaching, they immediately drop to the ground on their backs and quickly vanish into the soil.
There is one generation of these beetles per year. Adults overwinter in the soil and emerge in April and May to begin feeding and laying eggs. Each female can lay up to 450 eggs over a period of 3 to 4 weeks. The tiny, orange-brown eggs are laid in rows on the underside of lily leaves and the larvae begin hatching one to two weeks later.
The lily leaf beetle larvae are soft and slug-like. They are not pretty, but even worse, to protect themselves they carry their gooey, black excrement on their backs. Ingenious and disgusting.
The larvae are voracious eaters and the leaves of your lilies are soon gone. The flower buds turn black, wither and die. They feed for 3 to 4 weeks before moving down into the soil to pupate. About a month later they emerge as adult beetles and continue feeding before they return to the soil for the winter.
Most plants can generate new growth if their foliage gets eaten, but that is NOT the case with lilies. If lily leaf beetles eat the leaves, that’s it for the season and the plants may not have enough energy to return the next year. This makes it very important to be alert and catch the red beetles right away and prevent their damage.
Start scouting for lily beetles in late spring, shortly after your lilies emerge from the ground. You will need to sneak up and be prepared to grab them very quickly. Drop them into hot soapy water or use force to crush their shells. Inspect stems and leaves from all angles as the beetles hide in leaf crotches.
Destroying this pest’s eggs and larvae is equally important. Check your plants carefully at least twice a week, taking time to bend down and look under every leaf. Scrape off the larvae and remove the eggs. Wearing tight fitting rubber gloves makes the job a little easier.
There are two organic sprays that are relatively effective against the red lily leaf beetle. For both, spray coverage must be heavy and complete. Neem, an extract of the neem tree will kill young larvae. It should be applied every 5 to 7 days throughout early summer. Spinosad, an insecticide made from soil bacteria, is also effective if applied weekly. As with all insecticides, it is important to spray in the evening when bees are not foraging. Avoid spraying in windy weather when the spray may drift onto nearby flowers.
In some areas parasitic wasps are being released to keep lily leaf beetle populations in check. Don’t despair if you discover the red lily leaf beetle in your area. A combination of hand-picking and spraying the foliage weekly for the first half of the summer will keep this pest under control and let you continue to enjoy the beauty and fragrance of your lilies.