Control Lily Leaf Beetles | Gardening Advice
Both the grub (larva) and adult lily leaf beetle (also called the Asiatic lily beetle) feed on true lilies (not daylilies) in spring and summer. Left untreated, the lily leaf beetle will reproduce quickly and can kill your lilies.
The larva is really yellow or orange but looks black and gooey because it covers itself with its own excrement. If you prefer organic solutions to control lily leaf beetles, remove both the larvae and the adult beetles (careful—they jump and fly) by hand daily and crush them or drop them in soapy water to kill them. You’ll need to continue this process all season until no beetles or larvae remain and be vigilant the following year for survivors that overwinter in the soil.
Contact or systemic insecticides also will provide control. Biological controls are effective in Europe, and some are being developed here. Ask your local garden center for specific renovations.