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Tuesday - February 02, 2016

From: Brooklyn, NY
Region: Northeast
Topic: Pests, Shrubs
Title: Viburnum Leaf Beetle Damage to Native Viburnums
Answered by: Anne Van Nest

QUESTION:

Dear Friends, I am an officer of Protectors of Pine Oak Woods, a Staten Island, NY land conservation organization which also involves itself in forest restoration and invasive species control projects. In 2010 I became aware of viburnum leaf beetle damage (Pyrrhalta viburni) in Staten Island woodlands, reported that to the Cornell VLB site and began to glean what information was available on the web. Letters to local park managers revealed that some were already concerned and others were unaware of the presence of this beetle. Nowhere was I able to find any information about whether or not native viburnums in eastern US woodlands showed signs of recovery after infestation by the viburnum leaf beetle or what might be an effective control. Since then there has been a suggestion that basal stem painting with an appropriate adhesive might prevent many of the larvae from reaching the ground to pupate (perhaps OK for a formal planting but somewhat impractical in woodlands), and that the most effective solution - although labor intensive and necessary to constantly repeat - is to cut the egg depositions from viburnum stems in the fall and early winter. Nowhere could I find information about whether these techniques proved practical or effective, or any information about whether the affected areas might recover after beetle infestation. I write to ask if you can direct me to any current research or even anecdotal information about these issues. I am aware of the 2008 Weston paper about the loss of viburnums from VLB damage in grasslands and the edges of grasslands, but I am concerned about recovery of native understory viburnums in the woodlands themselves. Thank you for any attention that you might be able to give to my request. Sincerely, Protectors of Pine Oak Woods

ANSWER:

James Gyeltshen and Amanda Hudges at the University of Florida have compiled an extensive amount of information about the Viburnum leaf beetle on the UF/IFAS website. Here's some of their background material. Of interest is the list of preferred host food which will help with your future planning for your Staten Island woodlands.

The Viburnum leaf beetle (Pyrrhalta viburni), which is native to Europe and Asia, was first detected in North America in 1947 in Ontario, Canada, but established breeding populations were noticed only in 1978 in the Ottawa/Hull region of Canada (Becker 1979). The VLB slowly spread in the region, and was discovered later in Maine (1994) and New York State (1996) (Weston and Hoebeke 2003a). Subsequently it expanded its range towards the east and south, and given its host range diversity, it may become widespread. The viburnum leaf beetle (VLB) is distributed throughout eastern Canada and the northeastern United States, including parts of Maine, New Hampshire, Vermont, New York, Pennsylvania, Ohio, and most recently in Washington (Murray 2005, Weston and Hoebeke 2003). Although it is rapidly spreading southward, studies indicate that the southern range expansion might be limited by mild winters. VLB eggs require a prolonged chilling period (Weston and Diaz 2005).

Adults and larvae of VLB feed almost exclusively on species of viburnum (Wheeler and Hoebeke 1994). It has strong preference for arrowwood viburnum (Viburnum dentatum), European cranberry bush viburnum (Viburnum opulus), and Rafinesque viburnum (Viburnum rafinesquianum). Other species of viburnums include Sardent viburnum (Viburnum sargentii), wayfaring tree viburnum (Viburnum lantana), nannyberry viburnum (Viburnum lentago), and blackhaw viburnum (Viburnum prunifolium). In a summary of the findings of the Viburnum Leaf Beetle Citizen Science Project 2003, Weston (2003) categorized commonly grown viburnums into most susceptible, moderately susceptible and resistant species. The project aimed at monitoring the spread and damage of VLB in New York by involving knowledgeable and motivated citizens in meaningful scientific research program. Participants included landscapers, master gardeners, garden clubs, and school classes.

The study provided these results:

Most susceptible to VLB:

Viburnum opulus/trilobum - European cranberry bush viburnum
Viburnum dentatum - arrowwood viburnum
Viburnum sargentii - Sardent viburnum

Moderately susceptible to VLB:

Viburnum acerifolium
Viburnum carlcephalum
Viburnum lantana - wayfaring tree viburnum
Viburnum lentago - nannyberry viburnum
Viburnum macrocephalum
Viburnum pragense
Viburnum prunifolium - blackthorn viburnum

Resistant to VLB:

Viburnum burkwoodii
Viburnum carlesii
Viburnum lantanoides/alnifolium
Viburnum plicatum f. tomentosum
Viburnum rhytidiophylloides
Viburnum rhytidiophyllum
Viburnum sieboldi

Mechanical control: The best management option for VLB is to prune and destroy the infested twigs and branches during the winter. It is best to start monitoring the eggs after the first frost in the fall or winter. Egg laying sites are easy to spot when leaves are shed. Twigs with egg scars should be pruned off and destroyed from October through early May (Weston and Cramer 2006).

On a small scale, the adult beetles can also be collected and destroyed. VLB readily drop to the ground when disturbed and they can be collected in a soapy water by knocking the adults off the branches with a gentle tap (Ventresca and Kessel 2000, Weston and Cramer 2006). Repeated collections may be necessary as the beetles are likely to migrate from other infested areas.

When the VLB larva is ready to pupate in the soil, it crawls down the plant instead of directly dropping to the ground from the leaves. Trapping the larva with sticky barrier around the base is also suggested (Weston and Cramer 2006).

Cultural control: Use of species or cultivars less susceptible to VLB may also reduce the severity of infestation. Some of the resistant species of viburnum include: Viburnum burkwoodii, Viburnum carlesii, Viburnum lantanoides/alnifolium, Viburnum plicatum f. tomentosum, Viburnum rhytidiophylloides, Viburnum rhytidiophyllum, and Viburnum sieboldi (Weston 2003).

In addition, the Massachusetts Introduced Pest Outreach Project has the following additional cultural controls: Horticultural oil sprays applied to egg laying sites may reduce egg hatch by 75-80% (before leaves emerge in spring).

And finally, you might consider contacting Dr. Gaylord A. Desurmont, University of Neuchatel (Switzerland) Dr. Desurmont was doing quite a bit of research on Pyrrhalta viburni between 2008 and 2014. Many of his articles were published with co-author, Paul Weston at Cornell University. He seems to be the most prominent researcher studying this pest.

Best wishes with your quest to conquer the Viburnum leaf beetle.