Controlling Lily Leaf Beetles: Organic Methods to Protect Your Lilies

In my Gardener's Supply tenure, I've been staff horticulturist, retail nursery supervisor, product information specialist. For a natural teacher, avid gardener, and plant geek, this work is a perfect fit.

Twenty-five years ago, our old farmhouse yard was a blank lawn canvas. Native shrub/tree borders planted then now shelter/feed songbirds. Fertile soil supports productive vegetable gardens and flowering perennial beds. Added fruit/nut trees, blueberries, raspberries, elderberries feeding family and wildlife. Chickens and tropical houseplants occupy long New England winters. Education in horticulture/landscape design; authored four gardening books.

The adult lily leaf beetle. Photo: Ann Whitman

Colorful, hardy lilies have been perennial garden mainstays for generations. Sadly, in some regions gardeners have given up due to a small red beetle with insatiable appetite for lily foliage. Unchecked, lily leaf beetle devours leaves, leaving bare scarred stems instead of sturdy stalks with flamboyant trumpet blooms. Researchers study introducing natural enemies; meanwhile, safe organic methods help control this pest. In invaded regions, diligence protects lilies—but rewards (glorious flowers, delightful fragrance) are sweeter.

Accidentally introduced to North America via Montreal, Quebec in 1943; discovered in Massachusetts summer 1992. Scarlet lily leaf beetle (Lilioceris lilii) wreaks havoc wherever it travels. As of June 2012: all six New England states, New York, and near Bellevue, Washington. In Canada: Maritime Provinces (excluding Labrador/Newfoundland) west to Manitoba. Origin unclear; widely distributed in Europe, Asia, Middle East, North Africa.

Sierra Nevada, an Oriental type, is less susceptible to lily leaf beetles.

Preferred Host Plants

Lays eggs and completes life cycle exclusively on true lilies and fritillaria (daylilies unaffected). Oriental, rubrum, tiger, trumpet lilies, Oriental trumpets (orienpets), Turk's cap lilies, native North American species all vulnerable, but beetle prefers some. University of Maine research: Asiatic lilies most vulnerable; some Oriental lilies more resistant. Most resistant cultivars: Lilium henryi 'Madame Butterfly', Lilium speciosum 'Uchida', Lilium 'Black Beauty'. May impact native Canada lily (Lilium canadense) and other rare/endangered northeastern species.

Adults also eat: lily-of-the-valley (Convallaria majalis), Solomon's seal (Polygonatum), potato (Solanum tuberosum), flowering tobacco (Nicotiana), hollyhock (Alcea), hosta.

Identification

Egg masses on leaf undersides, red-orange to brown. Photo: Suzanne DeJohn

A chewed, defoliated lily may be your first sign. Both adult and juvenile phases are voracious, causing rapid damage. Examine lilies several times weekly from emergence. Adults overwinter in soil/plant debris, lay eggs early season, often starting on spring-blooming fritillaria emerging with daffodils. Each female lays up to 450 eggs, hatching in 1-2 weeks. Curb reproductive cycle early to prevent severe damage.

Adult: scarlet red top, black underneath, just under ½ inch, elongated body, long legs/antennae. Adults feed on foliage but primary concern is reproduction. If you see adults, check leaf undersides for egg masses—tiny, narrow, irregular rows.

Lily leaf beetle larvae covered in "fecal shield"

Larvae (grubs) cause most damage. Hundreds hatch at once, eat immediately. Prefer leaves but devour buds, flowers, stems. Most feeding under leaves or at leaf nodes. Larvae yellow/brown/orange but disguise effectively: pile excrement on themselves. Makes them hard to see (soft brown masses), hard to destroy (squishing doesn't necessarily kill), unpleasant to touch (some wear latex/nitrile gloves). Larvae feed 16-24 days, enter soil to pupate. Adults emerge 16-22 days later, feed until fall.

Controls

Spinosad Pest Control Spray

Biological control using natural predators shows most promise. No natural predators in North America, but University of Rhode Island Biological Control Lab (with CABI-Bioscience, French colleagues) identified European insects parasitizing lily leaf beetle grubs. Ant-sized parasitic wasps lay eggs on grubs, hatching and killing host. Released at research sites in all New England states, effective at decreasing populations for several miles. Not yet commercially available for gardeners, but long-term promise. See references for links.

Current gardener options:

Hand-picking adults: Effective for few plants. Must be vigilant and fast. Beetles drop to soil and lie on backs when sensing movement, making them hard to find. Use this: hold jar of soapy water under them, nudge off leaf—they fall in. Scout several times weekly, especially early season.

Destroy egg masses: Adults lay under leaves/along stems—destroy quickly (hatch in 7-10 days). Pick off leaf into soapy water or crush eggs. Tiny and hard—takes focused effort to ensure crushed.

Larvae control: Most difficult. Hand-picking requires near-daily patrols and careful observation. Squishing tricky due to fecal shield—slip between fingers. Wear gloves. Often easier to pick off whole leaf into jar.

Neem oil: Botanical insecticide from neem tree. Kills larvae, repels adults. Most effective early season on young larvae; apply every 5-7 days. Fecal shield provides some spray protection—coverage must be heavy/complete. Late-season larvae somewhat resistant.

Spinosad: Derived from soil bacterium. If used regularly at first sign, controls beetles.

Other insecticides effective but environmental concerns: impact on beneficial non-target insects. Imidacloprid-linked to honeybee death and colony collapse disorder—makes nectar/pollen toxic to bees.

More Information

• Invasive Species Compendium (CABI)
• Center for Invasive Species and Ecosystem Health, Assessing Host Ranges for Parasitoids and Predators, Van Driesche & Reardon eds., Ch. 10
• University of Massachusetts, Lily Leaf Beetle Fact Sheet
• University of Rhode Island, Lily Leaf Beetle Fact Sheet
• Washington State University Extension, Pest Alert: Red Lily Leaf Beetle
• Harvard School of Public Health, "Use of Common Pesticide Linked to Bee Colony Collapse"