Products with spinosad offer one more control option for lily leaf beetles.

Flower gardeners are a peaceful lot—at least until someone comes between them and their favorite blooms. Then, they get mean. At least some of us do.

It was about three years ago that I first heard whisperings in the halls at Gardener’s Supply of a new pest: “Something is destroying my Oriental lilies! What can I do?” The unspoken reply: “How far are you willing to go to save your lilies? Will you use chemicals?”

The culprit, the lily-destroyer, the evil insect is Lilioceris lilii, aka: The Lily Leaf Beetle. Oh, these scarlet beauties are striking in the garden. But then they breed and their disgusting offspring take over, devouring the lilies and covering themselves in their own poo.

The devastation brings out bloodlust in some gardeners—even the earth-friendly ones. At first, I tried neem, a relatively harmless spray that does wonders on aphids and controls blackspot on roses. It worked to control the larvae the first year, but I had to spray frequently (every 10 to 15 days). The second year, I couldn’t keep the larvae under control. My lily crop was hit hard, and I got few blooms. Last year, I decided to resort to a systemic called imidacloprid. The results were instantaneous and effective. No more poo-covered larvae; no more devastation.

Larvae of the lily leaf beetle

The eggs of the lily leaf beetle are usually found on the underside of the leaves, as shown on this fritillaria. They’re smaller than poppy seeds, and usually bright red. If you see these, you’ve got a problem.

Still, imidacloprid is not something I can feel good about. Systemic insecticides are harsh. Plus, studies have shown that imidacloprid can be harmful to bees, so I’m giving it up. I need a new approach.

I’ve been reading about something new, a substance called spinosad, which is made from a soil-dwelling bacterium, Saccharopolyspora spinosa. The sprays are said to control foliage-feeding caterpillars, beetles, borers and other pests. When used carefully (read the label!), it’s not supposed to effect beneficial insects. Plus, spinosad has been classified as an organic substance by the USDA National Organics Standards Board. This year, I plan to try Monterey Garden Insect Spray, which is one of the formulations. I’ll let you know how it goes. Have you seen lily beetles in your area? Let me know what works for you by posting a comment, below. Already I’ve had reports from two customers: one infestation on fritillaria and another on Asiatic lilies. Both sites were treated with spinosad.

In the meantime, keep your fingers crossed that researchers will find something that can be used to keep these pests in check. According to David Sims of the North American Lily Society, there is concern that the beetle will wipe out native lily populations. The group has been a sponsor of a study at the University of Rhode Island, where researchers are using predatory wasps to control the beetle. So far, the results have been encouraging.

-David Grist, Online Content Coordinator