Viburnum Leaf Beetle Pyrrhalta viburni (Paykull) in the Nursery and Landscape
Recently, this beetle, closely related to the common elm leaf beetle, Pyrrhalta luteola (Mhller), has become a concern in many urban landscapes and nurseries. It can strip the leaves from viburnums in a relatively short period of time.
Originally from Europe and Asia, established breeding populations were first recorded in 1978 in the Ottawa-Hull area.
Both the adult and larva feed on viburnums.
Look for skeletonized leaves. Both the adult and the larva feed on the leaves between the midrib and larger veins. This gives the leaves a lace-like or skeleton appearance. Plants which have been defoliated for 2 or 3 consecutive years may be killed. Closely examine the small twigs for egg laying holes and scars.
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 injury appears as small pin pricks or holes. By June the skeletonizing has become quite apparent.
In June, larvae drop or migrate to the ground to pupate in the soil. Adult beetles emerge in late July. They are about 4.5 to 6.5 mm in length and brown in colour. When disturbed, they will fly away or drop to the ground.
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. Egg laying holes can be found in a straight line on the underside of the current season's growth. A single female may lay up to a total of 500 eggs per season.
The beetle's life cycle, from egg hatch to adult takes about 8 to 10 weeks.
In the early spring, closely examine the small twigs from the previous season. Look for the overwintering egg sites. As the temperature increase, these holes appear to swell and the caps of the holes fall off. Prune out and destroy affected wood before egg hatch has occurred.
Once leaves have begun to expand, examine both the surface and the underside for feeding larvae.
If chemical controls are to be used, best control will probably be achieved if applied while larvae are young. Adults may be more difficult to control as they will fly away or drop to the ground if disturbed.
For chemical controls, consult Ontario Ministry of Agriculture, Food and Rural Affairs Publication 383, Production Recommendations for Nursery and Landscape Plants.
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