Common name: Viburnum crown borers
Scientific name: Synanthedon viburni and Synanthedon fatifera
Hosts: Viburnums (Viburnum species) are the hosts for the viburnum crown borer. The borer feeds as larvae, on the lower part of viburnum trunks, branches, and roots. There are two species which have a similar look and biology, viburnum crown borer (Synanthedon viburni) and the lesser viburnum crown borer (S. fatifera). These insects can seriously damage or kill the host plant. These insects are found across most of the Eastern United States.
The larva of the viburnum crown borer is the damaging stage. The larvae tunnel under the bark of the main trunks and roots and may be found anywhere from a few inches below the soil line up to 18 inches above the soil line. The first symptom noticed is dieback of entire branches. Other symptoms include swellings, cracks and emergence holes at the base of the plants. Ultimately, the entire plant may die.
Viburnum crown borer overwinters as larvae under the bark of the host. In spring, usually in late May, they will pupate and then emerge as adults in June. The adults are day-flying moths. They look similar to wasps and are classified as clearwing moths. They have one-half inch long, bluish-black bodies with yellow markings and clear wings, with a three-quarter inch wing span. The newly emerged adults will mate and then lay eggs near wound sites. The eggs hatch and the young larvae tunnel under the bark and feed on the cambium and inner bark. They will remain there for the rest of the season and through the winter. Larvae are legless and white in color, with reddish brown heads.
Cultural management:
Viburnum crown borers are attracted to stressed plants. Plants should be sited properly. Keep them healthy by watering in dry periods and mulching properly. Prevent injuries and wounds such as those caused from weed whips, lawn mowers, and improper pruning.
Biological management:
Beneficial nematodes (Heterorhabditis bacteriophora) can be applied as a soil drench in late August. To ensure that the nematodes stay alive, the soil should be kept moist.
Chemical management:
Susceptible viburnums can be protected with an insecticide sprayed on the bark of the plant from the soil line to about 18 inches high. Timing is critical. Spray while adult moths are active, typically in June. The insecticide is targeted at killing newly hatched larvae before they enter the bark.
The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. Use pesticides safely and wisely; read and follow label directions. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.
For more information, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).