The appearance of holes, notches, and chewed foliage on lilies requires accurate identification of the culprit for effective treatment. Damage to lily leaves is detrimental because the plant relies on this foliage to create the energy needed to produce next year’s bulb and flowers. Understanding the distinct signs left by different garden invaders allows for a targeted approach to pest management.
The Tell-Tale Signs of the Lily Leaf Beetle
The most significant threat to true lilies (Lilium species) is the non-native scarlet lily beetle (Lilioceris lilii). The adult beetle is instantly recognizable by its bright, glossy scarlet body, which contrasts sharply with its entirely black head, legs, and antennae. Measuring about a quarter-inch in length, these voracious feeders create irregular holes and notches in the leaves, stems, and developing flower buds shortly after emerging from the soil in spring.
Adult beetles use a defense mechanism called thanatosis, quickly dropping off the plant when disturbed and landing on their black undersides, making them nearly invisible against the soil. Females lay tiny, orange-red eggs in irregular lines along the undersides of leaves. These eggs hatch within one to two weeks into the destructive larval stage. The slug-like larvae, which are soft and yellowish-white, employ a unique form of camouflage.
The larvae cover themselves in dark excrement, forming a “fecal shield” that protects them from predators and the sun. This larval stage causes the most severe damage, feeding continuously for three to four weeks and often skeletonizing leaves until only the main veins remain. If left unchecked, both the adults and the larvae can completely defoliate a lily plant, severely diminishing the bulb’s energy reserves and compromising flowering for the following season.
Damage Caused by Slugs, Snails, and Other General Pests
While the lily beetle is highly specialized, other common garden pests also damage lily leaves. Slugs and snails, which are nocturnal feeders preferring moist environments, leave behind large, ragged, and irregular holes, often chewing through the center of the leaf or along the margins.
The most reliable sign of slug or snail activity is the presence of shiny, dried slime trails left on the leaves, stems, or surrounding soil. They are especially damaging to newly emerging lily shoots in the early spring, sometimes consuming the tender growth completely. Caterpillars, such as the lily caterpillar, leave behind larger, cleaner-cut holes than mollusks, and young ones may initially skeletonize leaves.
Damage caused by larger animals like rabbits and deer is distinct from insect or mollusk feeding, as lilies are a preferred food source for both. Mammalian damage is identified by a sharp, clean cut or tear on the stem or foliage, often near the ground for rabbits or higher up for deer. Deer especially target tender new growth and flower buds, and a sudden, extensive loss of the plant’s upper portion suggests a mammal was the culprit.
Effective Ways to Stop the Pests
An integrated pest management (IPM) approach combining mechanical removal and organic treatments is the most effective way to protect lilies. For the scarlet lily beetle, consistent handpicking is the primary non-chemical control method. Adult beetles should be removed immediately upon sighting, typically by holding a cup of soapy water beneath the leaf and nudging the beetle into the solution to prevent their escape into the soil.
The eggs and larvae must also be addressed, requiring gardeners to check the undersides of leaves at least twice a week throughout the early growing season. Eggs can be crushed, and larvae should be scraped off using gloves and destroyed, as the fecal shield makes them resistant to handling. Organic sprays containing neem oil or spinosad are effective against the young larvae. Neem oil works best when applied thoroughly every five to seven days, targeting the underside of the foliage where the larvae feed.
Managing slugs and snails involves reducing their access and creating barriers. Removing debris, excess mulch, and hiding spots around the lilies reduces the moist habitat they require. Diatomaceous earth can be sprinkled around the base of the plants; this fine powder causes desiccation when slugs and snails crawl across it. Beer traps, which involve sinking a shallow container of beer into the soil, attract and drown these pests.
For larger pests like deer and rabbits, physical barriers or repellents are necessary. Fencing or netting can be installed to block access entirely, which is the most reliable method against persistent feeding. Repellents containing ingredients like clove oil or putrid egg solids can be sprayed on the foliage to make the plants unpalatable, though reapplication is necessary after rain or every seven to ten days.