In the Garden:
New England
July, 2009
Regional Report

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Left unchecked, lily leaf beetles can decimate lily foliage.

Lily Leaf Beetle

If you grow lilies, you're probably familiar with the scarlet lily leaf beetle (Lilioceris lilii). And if you don't know this pest, be on the lookout. Both the larvae and adult beetles eat lily foliage; a bad infestation may reduce plants to naked stems.

A European native, lily leaf beetle was discovered in Montreal in 1945 and seemed confined there for decades until it found its way to Massachusetts in 1992. Since then, it has spread rapidly and is now a major pest across the Northeast.

Lily Beetle Life Cycle
The adult beetles are about a half-inch long and bright red, with black legs and antennae. They emerge from hibernation around the time lilies sprout, and the adults begin feeding and laying eggs on the undersides of leaves. The eggs hatch in four to seven days and the voracious larvae begin eating.

After two to three weeks the larvae drop to the ground to pupate. A few weeks later, they emerge as adults and again begin feeding on lily foliage, continuing to do so through the rest of the growing season. The adults overwinter in soil or plant debris.

Control
While the adult beetles are easy to spot and hand pick, the larvae are more of a challenge. Not only are they harder to see, they have the particularly offensive habit of piling their own excrement on their backs as they feed, rendering them slimy and difficult to squish. This protective covering also makes them challenging to control with sprays.

Some gardeners report limited success using neem oil. However, a relatively new pest control product called spinosad appears promising in controlling not only the lily beetle, but other garden pests as well. Spinosad is made from the fermentation of a naturally occurring soil bacteria. This organic biological pesticide is also effective at controlling caterpillars, leaf miners, thrips, and fire ants. It's sold under various trade names; read pesticide labels, looking for spinosad as the active ingredient. Spinosad attacks the nervous system of the pests, causing them to eventually become paralyzed and die.

Lily leaf beetle lays its eggs only on true lilies (that is, in the genus Lilium) and fritillaria. True lilies include Asiatic and Oriental lilies, as well as tiger lilies, turk's cap lilies, and Easter lilies. However, the beetle has been observed feeding on other plants, including hollyhock and hosta. It is not a pest of other "lilies" such as daylilies, calla lilies, and water lilies, none of which are true lilies.


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