The viburnum leaf beetle (VLB) (Pyrrhalta viburni) is a non-native invasive species that is making Ohio its home - well at least some of the buckeye state. While the insect has been detected and is known to be in the northern portion of the state, we are encouraging all Ohioans to monitor for the pest and become aware of signs and symptoms if you aren't familiar with exotic invader.
Last week, Mary Visco, horticulturist with the Toledo Botanical Garden (TBG) in Toledo, Ohio was scouting the viburnums in the Garden and noticed first instar larvae had hatched and began feeding. Last year (2016), was the first time the insect had been identified in Lucas County in several locations in the county including TBG.
This insect overwintered in the egg stage in "pits" created by mated females on twigs of the viburnum shrubs last year. The newly hatched larvae tend to feed side-by-side on the underside of the leaves between the veins of the leaf. Frequently the young larvae lay parallel to the leaf veins making it a challenge to see them when they are very small. This is exactly what Mary saw and brought to the attention of the Extension office.
The larval feeding initially appears as skeletonizing where both the lower leaf surface and middle layer of the leaf is consumed and upper leaf surface is left intact. This damage will become more exaggerated as the leaf continues to mature and expand resulting in the skeletonized areas ripping out from between the veins, leaving only midribs and major veins intact. As the larvae grow, their feeding becomes more aggressive and holes are produced through the entire leaf. Heavy feeding by the larvae can result in leaf drop to total defoliation.
So if this pest is new to you, where do you start looking? Weston (2003) classified a number of common viburnum species into categories of most susceptible, moderately susceptible, and least susceptible species based on a multitude of field observations. If you plan to scout, efforts should be focused on viburnums in the most susceptible category. Below is a summary of the viburnums mostly found in Ohio and appears in the OSU Viburnum Leaf Beetle FactSheet AGR-39:
Most susceptible viburnums:
- Arrowwood viburnum (V. dentatum)
- European cranberrybush viburnum (V. opulus)
- American cranberrybush viburnum (V. opulus var. americanum = V. trilobum)
- Rafinesque viburnum (V. rafinesquianum)
Moderately susceptible viburnums:
- Sargent viburnum (V. sargentii)
- Wayfaringtree viburnum (V. lantana)
- Nannyberry viburnum (V. lentago)
- Blackhaw viburnum (V. prunifolium)
Least susceptible viburnums:
- Koreanspice viburnum (V. carlesii)
- Burkwood viburnum (V. burkwoodii)
- Doublefile viburnum (V. plicatum var. tomentosum)
- Judd viburnum (V. x juddii)
- Lantanaphyllum viburnum (V. x rhytidiphylloides)
- Leatherleaf viburnum (V. rhytidiphyllum)
Check out the complete OSU FactSheet written by Curtis Young online at http://ohioline.osu.edu/factsheet/anr-39
Detection is the first step. If you suspect you found the VLB, reports can be made on the Great Lakes Early Detection Network (GLEDN) App: https://apps.bugwood.org/apps/gledn/ This App is a great way to monitor the spread of VLB and other invasive pests including insects, diseases and plants.
Stay tuned to BYGL for future updates of VLB as the season, and damages, progress.