Authors: PJ Liesch and Phil Pellitteri (retired) UW-Entomology
Revised: 01/30/2026
Item number: XHT1046

Viburnum borers are the larvae (caterpillars) of species of clearwing moths (Family Sesiidae), specifically associated with viburnums. The larvae tunnel into the stem and branches at the base of the plant which can lead to branch dieback, plant decline, and eventual death of viburnums.  Heavily infested plants appear unhealthy, and often show swelling, cracks, and emergence holes at the base of the plant. Two species of clearwing borer moths, the viburnum clearwing borer (Synanthedon viburni) and the lesser viburnum borer (Synanthedon fatifera), are associated with viburnums in Wisconsin.

Appearance: Adults of both the viburnum clearwing borer and the lesser viburnum borer are day-flying moths that mimic the flight and appearance of wasps. They are slender, bluish-black moths with yellow markings, clear wings, and a wingspan of 3/4  inch. Larvae (caterpillars) are whitish or pinkish with brownish heads and reach lengths of up to 5/8 inch.

Life cycle and damage: Viburnum borers have one generation per year in Wisconsin. Damage is caused by the caterpillars and is typically restricted to the lower 18 inches of the plants. After emerging in late spring and early summer, adults mate and lay eggs near the base of viburnums, especially near wounds in the bark.  After hatching from the eggs, the caterpillars tunnel into the plant and feed on the bark and cambial tissues.  Gnarled and scarred stems with sawdust are indicators of attack. Swellings and callus growth indicate the healing of old injury sites or long standing damage.  Over time this tunneling will cause distortions and swellings on the main stems and branches.  In addition, wounds caused by viburnum borers can serve as potential entrance points for plant diseases.

Management:

Non-chemical management: Strong, vigorous plants are less attractive to borers and more likely to survive attack. Good plant maintenance (e.g., proper pruning, watering, and prevention of bark injuries) will help reduce problems. There are some differences in susceptibility of different viburnum species and cultivars.  Planting viburnums that are less-preferred, can be another consideration for new plantings.  Also consider removing plants that face significant attack. Plants that require high maintenance and yearly pesticide treatments are not ideal.

Chemical management: Insecticides can be used around the time that adult moth are laying eggs to help prevent infestations. Treatments will create a protective coating and will kill small caterpillars as they attempt to tunnel through the bark. Timing is important—if larvae are already under the bark, they are protected and insecticide treatments will not work.  

To help pin-point the ideal timing of treatments, pheromone traps can be obtained through online vendors (e.g., Great Lakes IPM).  These traps monitor for the adult activity in spring.  Spraying once adults have become active will help prevent infestations. Insecticide options exist for both homeowners and professional landscapers.  Choose a product from the pyrethroid group (e.g., bifenthrin, cypermethrin, cyhalothrin, permethrin, etc.) labeled for use on landscape trees and shrubs. Apply the product to the bark of the lower 18 inches of the plants. If traps are not available to aid in the decision-making process, apply insecticides during mid-June and in heavy infestations reapply in mid-July.

Thanks to Karen Delahaut and Chris Williamson for reviewing previous versions of this document.