Print Version

Description:

The Viburnum Beetle (Pyrrhalta viburni) is a beetle closely related to the common Elm Leaf Beetle. It can strip the leaves from Viburnums in a very short time. Originally from Europe and Asia, established breeding populations were first recorded in 1978 in the Ottawa-Hull area. They are commonly found in Southern Ontario. The adults are present from July to September.

Adults are somewhat difficult to see. They are only about 4.5 to 6.5 mm in length (1/4 inch), with browish coloured head, thorax and wing covers. Females are slightly larger.

At maturity the yellowish brown, cylindrical larvae (somewhat depressed) are about 10 to 11 mm long (1/2 inch).

The brownish black egg caps are 1 -2 mm in diameter can be found in straight lines under the surface of terminal twigs.

Symptoms of Viburnum Leaf Beetle Infestation:

Look for skeletonized leaves. Both the adult and larva feed on the leaves between the midrib and larger veins. The holes created give the foliage a lace-like appearance. Much of the remaining leaf tissue turns brown. Damage is often very extensive. The damage can result in the vigor of the shrub being compromised or weakened. Plants that have been defoliated for two or three consecutive years may be killed. Closely examine the small twigs for egg laying holes and scars. Egg laying holes are often found in a straight line on the underside of the current season's growth.

Plants Affected:

Viburnum opulus (European highbush cranberry) and V.lantana (Wayfaring Tree) are host plants. Others may be affected but suffer little or no damage (e.g. V. rafinesquianum (Rafinesque viburnum), V. dentatum (Arrowwood), V. trilobum (American Highbush Cranberry), V. acerifolium (Mapleleaf viburnum) and V. lentago (Nannyberry).

Life Cycle and Habits:

Viburnum leaf beetles overwinter as eggs. Eggs hatch in May and the larvae begin feeding on the developing leaves. The larvae are quite small and darkly coloured when they first emerge. First feeding damage looks like small pin pricks or holes. The skeletonizing is quite apparent by June.

In June, the larvae drop to the ground and pupate in the soil. Adult beetles emerge in late July. They are 4.5 to 6.5 mm in length and brown in colour. When disturbed, the beetles will fly away or drop to the ground. The adult beetles continue to feed on what remains of the leaves, then they mate and lay eggs in the shrub's twigs.

Females lay eggs from late summer to the first frost. A hole is chewed in the small twigs. Several eggs are laid in each hole, which is then covered with a mixture of chewed wood and excrement. A single female may lay up to 500 eggs per season.

The beetle's life cycle, from egg hatch to adult, takes 8 to 10 weeks.

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.

Mechanical Control:

• In early spring, closely examine the small twigs from the previous season. Look for overwintering egg sites. As the weather becomes warmer, these holes appear to swell and the caps of the holes fall off. Prune out and destroy affected wood before egg hatch has occurred. One source suggests the use of dormant oil will help control the number of eggs that hatch.
• Once the leaves have begun to expand, look closely at both the surface and the underside of the leaves for larvae feeding.
• Avoid planting species that are particularly susceptible.

References:

• The Toronto Botanical Garden Weston Family Library is an excellent source for horticultural information.
• Yepson, Roger B.Jr. ed. The Encyclopedia Of Natural Insect and Disease Control. Pennsylvania, U.S.A.: Rodale Press, 1984.
• Cranshaw, Whitney. The Ultimate Guide to Backyard Bugs. Princeton, U.S.A.: Princeton University Press, 2004.
• Alford, David V. A Colour Atlas of Pests of Ornamental Trees, Shrubs and Flowers. Portland, Oregon: Timber Press, 2003.
• The Gardener's Handbook - An Integrated Approach to Insect and Disease Control, Toronto, Canada: Publication 64. Ontario Ministry of Agriculture, Food and Rural Affairs, Queen's Printer for Ontario, 1998.

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