Hello,

The damage to your lilies is caused by the lily leaf beetle. Lily leaf beetles can be a destructive nuisance—to the point that they can kill the plant. Cutting the plant down is one solution but does not mean that you will eradicate the beetles. There is only one generation per season but they overwinter as adults in soil, plant debris and other sheltered areas. The next spring, the adults who are strong fliers emerge to seek out host plants. Read about the lily leaf beetle and how to manage it here: https://hort.extension.wisc.edu/articles/lily-leaf-beetle/

And here: https://www.canr.msu.edu/news/lily_leaf_beetle_watch_out_for_this_garden_pest

In addition to hand picking they can be treated with insecticides which, sadly, may also affect friendly insects, pollinators and predators.

As a solution, replace the lilies with other perennials. There are lilies that are not susceptible to the beetle such as daylilies.

If you do choose to treat with insecticide, read the label to ensure that the insecticide can be used on lilies and follow the directions on the proper application of the chemical.

Thank you for contacting Ask Extension.