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Description:

The adult lily-leaf beetle is about 3/8 inch or 9 mm in length, with shiny red wing covers that contrast sharply with a black head, antennae (11 segments), legs and underside. Larvae are reddish brown with black heads (somewhat slug-like in appearance) covered with dark, slimy excrement. The adult beetle can produce chirping sounds, often when picked up.

Symptoms of Lily-leaf Infestation:

Both adults and larvae kill lilies by feeding on the leaves, and then the flowers. This pest causes devastating damage, weakening the lilies, making them susceptible to disease such as Lily grey mold.

Plants Affected:

This insect is a pest of lily species (Lillium spp.), Lily of the valley (Convallaria majalis), Solomon's seal (Polygonatum multiflorum), in addition to the fritillary (Fritillaria spp.).

Life Cycle and Habits:

The adult beetle emerges from the soil in early spring, after overwintering in plant debris or soil. It lays its yellowish, cylindrical eggs (200 to 300) in clusters or rows, on the undersides of leaves of young lily plants. Some beetles can survive two years and lay eggs each year. The newly hatched larvae feed on the underside of leaves, while mature larvae feed on the upper surface of the leaves. The larvae are usually coated with a protective covering of excrement. There may be 1 to 3 generations per year. A long egg laying and emergence period makes control difficult (mid-spring to mid-summer).

Organic Management/Control Strategies:

The City of Toronto adopted a new municipal by-law (spring 2004) that restricts the use of pesticides. For details about the by-law visit the Pesticide by-law page on Toronto Public Health's Web site at www.city.toronto.on.ca/pesticides or www.toronto.ca/health. Questions may be e-mailed to pesticide@toronto.ca.

Organic Control:

• The botanical insecticide Neem can be applied. It is most effective when applied to the newly hatched larvae.

Mechanical Control:

• Handpicking in the early morning is the best solution, throwing the captives into soapy water.
• Spray plants directly with insecticidal soap.
• You can also search for the eggs and destroy them.

Cautions and Considerations:

Early detection is the key. It is important to catch them right at the beginning or your lilies will be completely destroyed. They are more likely to be present after a mild winter.

References:

• The Toronto Botanical Garden Weston Family Library is an excellent source for horticultural information.
• Cole, Trevor (ed.).Practical Guide to Gardening in Canada. New York, U.S.A.: Dorling Kindersley, 1993.

Factsheets are produced by the Toronto Master Gardeners in association with the Toronto Botanical Garden. They provide introductory information about a broad range of horticultural topics and are intended for personal use and study purposes. Should your gardening group or organization wish to use multiple copies we ask that you inform the Toronto Botanical Garden at info@torontobotanicalgarden.ca.

Date revised: January 8, 2006