Gazette Gardener: Destructive lily leaf beetles make a local garden appearance

I’ve got another voracious insect to tell you about. It’s the lily leaf beetle and it has been found
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I’ve got another voracious insect to tell you about.

It’s the lily leaf beetle and it has been found in Schenectady and several other counties in upstate New York.

Native to Europe, they have been known to be in Canada since 1945, and in Cambridge, Mass., since 1992 when they arrived as stowaways in a shipment of bulbs from Europe.

The beetles are strong fliers but it is generally believed that gardeners and suppliers may have been unknowingly helping the spread by transporting the beetles from one area to another on host plants.

And while this insect is — as insects go — a pretty thing to look at with its distinctive bright red color, it is definitely a serious pest for gardeners growing true lilies and other host plants as both larvae and adults are capable of causing significant damage.

Not just lilies

To be very clear, they are not a pest on day lilies. They lay their eggs and are therefore a major problem on all true lilies, including the showy and commonly grown Asiatic and oriental lilies, and on Fritillaria species. In addition, researchers in Rhode Island have found adult lily leaf beetles feeding on other host plants including Solomon’s seal (Polygonatum sp.), Bittersweet (Solanum sp.), Potato (Solanum tuberosum), Hollyhock (Alcea), and various Hosta species, according to the University of Massachusetts Extension fact sheet on the beetle.

Chris Logue, executive director for Cornell Cooperative Extension, Schenectady County, said that they have been watching the progress of the lily leaf beetle in the Northeast and recently a homeowner from the Altamont area of Schenectady County “brought a sample of damaged lilies into our office along with several insects that turned out to be lily leaf beetles.”

This gardener had a planting of lilies that had been there 25 to 30 years, he added. He noted that on the USDA Invasive species website, the beetle presence in the county had been detected by survey in 2009 but this is the first time a homeowner has brought the insect to the extension office for identification.

This insect is so distinctive in every stage of its development that homeowners should be able to spot them in the garden and identify what they are. As an adult it is about a half inch long with a red body and black legs, head and antennae. The underside of the insect is black.

Adults overwinter in secluded, sheltered places and not necessarily near the host plants. Once they emerge in April, they begin to forage for food and seek a mate. Adult females lay their eggs in irregular lines on the undersides of the foliage.

“These reddish-brown eggs start to appear in April-May and hatch within 4-8 days. The young larvae initially feed on the undersides of the foliage but can later be seen on the upper surfaces and the buds. The larval feeding period is the most destructive and lasts for 16-24 days. They then drop to the soil to pupate and new adults emerge 16-22 days later and can be seen feeding throughout the rest of the growing season,” the fact sheet states.

The female can lay up to 450 eggs over her lifetime. And the larvae, which have a black head and an orange, brown or green body, have been described as slug-like. If that alone isn’t grotesque enough, they carry their excrement around on their backs.

“It must be some sort of defensive mechanism. It makes them look like a bird dropping, warding off predators and parasites. Tortoise beetles, for example, put fecal material on their backs for that reason,” Cornell entomologist E. Richard Hoebeke is quoted as saying in a Cornell University fact sheet on the beetle.

This life cycle repeats until cold weather sets in when the lily leaf beetle retreats into the soil or plant debris where it will overwinter.

Management

Logue suggested controlling the pest, by hand picking of the larvae, adults and eggs, is possible. “If you can’t stand handling the larvae with your bare hands, wear rubber gloves,” he said. Insecticidal soaps work on the larvae “because they are soft bodied,” he added. Insecticidal soap will not work as well on adult beetles.

The University of Massachusetts Extension website noted that neem products have been shown to kill larvae (especially the very young ones) and to deter the adults, but applications may need to be administered early in the growing season and then repeated with some regularity (weekly) in order to achieve the desired level of effectiveness.

As gardeners, one of the best approaches we can take is to inspect host plants we already having growing in our gardens carefully. Early detection can keep a problem from spreading.

And, when we are out buying plants, take the initiative and the time to examine prospective purchases carefully. By doing so we can avoid unintentionally bringing more back to our gardens than we planned.

Invasive Ash Borer

Being careful can also help with the spread of another pest, the Emerald Ash Borer which was found in mid-July in Steuben and Ulster counties in New York. This beetle has killed millions of ash trees in Canada and the Midwest. State environmental officials believe the insect is being transported into new areas by campers hauling firewood. Something as simple as buying firewood locally can help slow down this pest and protect the state’s 900 million ash trees.

Happy gardening.

Natalie Walsh is a horticulturist, speaker and garden consultant. She can be reached at [email protected]

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