The clever behavior of creating shields from their own excrement allows immature lily leaf beetles (Lilioceris lilii) to hide from predators. Under this fecal defense, larvae feed on lilies (Lilium spp.), undisturbed, for up to 24 days. With multiple species and hybrids, lilies grow across the country in U.S. Department of Agriculture plant hardiness zones 3 through 9. The invasive lily leaf beetle, first discovered in the U.S. in 1992, is most problematic in the eastern states, with only a few incidents of the pest reaching as far as the West Coast. Research into the best control methods is ongoing, but there are a few effective ways to rid your lilies of these destructive beetles.
Bright red adult lily leaf beetles emerge in early spring and immediately feed on lily shoots. This is the best time to stop the spread of the beetles, before they begin laying eggs. Hand pick the pests off your lilies and drop them into a bucket of soapy water. Gently shake the plant over the bucket since these insects often drop to the ground when disturbed. Lily leaf beetles lay clusters of orange-brown eggs on the undersides of leaves. Larvae hide under their black, slimy fecal shield while feeding. Frequently monitor lilies for eggs and larvae throughout the growing season. If they are too difficult to hand remove, pick off the entire infested leaf.
Insecticidal products containing the oil from neem tree seeds are effective against the early larval stages of lily leaf beetles, shortly after egg hatch. Mix 6 tablespoons of concentrated neem insecticide with 1 gallon of water into a garden sprayer and shake well. Spray all plant surfaces, paying close attention to the undersides of leaves. Repeat the application every five to seven days. Avoid inhalation of the mist and protect eyes, skin and clothing while spraying. Neem products are hazardous to aquatic wildlife. Avoid using this insecticide on or near water areas.
If you live in an area where lily leaf beetles are a problem, consider choosing pest-resistant lily hybrids for your garden. Hybrid lilies are typically separated into two groups -- Asiatic and Oriental hybrids. Those in the Asiatic group bloom in spring and early summer, while Oriental hybrids are late bloomers. Asiatic lilies are more susceptible to lily leaf beetles. Oriental hybrids, particularly Lilium henryi “Madame Butterfly” (USDA zones 5 through 8), Lilium speciosum “Uchida” (USDA zones 4 through 9) and Lilium “Black Beauty” (USDA zones 3 through 8) are significantly resistant to the lily leaf beetle, reports the University of Rhode Island Department of Plant Sciences.
Lily leaf beetles are less of a problem to lilies in Europe because there are predators there to keep populations in check. As an introduced species to North America, the beetles have no natural enemies here. The University of Rhode Island conducted controlled releases of tiny European parasitic wasps that specifically target lily leaf beetle larvae. Preliminary research shows that the wasps are becoming established in New England and reducing lily leaf beetle populations. The wasps are not yet commercially available, but you can encourage them into your garden by avoiding the use of broad spectrum, residual insecticides.
- UMass Extension, Landscape, Nursery and Urban Forestry Program: Lily Leaf Beetle
- Missouri Botanical Garden: Plant Finder -- Lilium
- Washington State University Extension: Pest Watch -- Lily Leaf Beetle
- North American Lily Society: The Lily Leaf Beetle (Lilioceris Lilii) -- An Unwelcome Invader
- University of Rhode Island, Department of Plant Sciences: Lily Leaf Beetle Resistance Among Lily Hybrids
- The University of Maine Cooperative Extension: Lily Leaf Beetle
- UMass Extension, Greenhouse Crops and Floriculture Program: Production of Hybrid Lilies as Pot Plants
- Plants for a Future: Lilium speciosum
- University of Rhode Island, Department of Plant Sciences: Establishment of Parasitoids of the Lily Leaf Beetle (Lilioceris lilii) in New England
- Photo Credit DreamyHarry/iStock/Getty Images
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