Viburnum nudum, Part Deux

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  Note: As you await tonight’s Election results, situated in front of your TV or at watch parties, here is something horticultural for you to vote upon: should you plant Viburnum nudum?  Read on.  

  On October 28, 2016 we did a bygl-alert for the Shrub of the Week as Viburnum nudum (http://bygl.osu.edu/node/627). Quickly we had some responses noting that, for example “…it might be helpful to include V. nudum's susceptibility to infestation by the Viburnum Leaf Beetle. http://www.hort.cornell.edu/vlb/suscept.html.”

 

Viburnum leaf beetle feeding damage

 

  This came from Steve Herminghausen, a Master Gardener Volunteer from central Ohio, wondering if this is a good selection to highlight for those there worried about this invasive pest moving into their area.  This is exactly what we hope Master Gardener Volunteers to do relative to channeling research-based information.

  In that Cornell publication Steve listed, Viburnum nudum (possum-haw, smooth witherod) is listed in their category for:

  “Highly susceptible species are the first to be attacked, and are generally destroyed in the first 2-3 years following infestation.”

  To add to this, the highly knowledgeable Charles Tubesing, the Plant Collections Curator of Holden Arboretum notes:

  “We no longer have any V. nudum in our plant collection. Our policy is not to attempt to control chronic pests. We want to be able to display and recommend sustainable plant selections for gardens. We don't spray for VLB, which has meant that our viburnum collection has been reduced to the less susceptible taxa.. An interesting observation has been that, although V. dentatum has been eliminated from plantings by VLB, plants growing at riparian edges have survived, though they do sustain foliage injury.”  

 

viburnum leaf beetle larval feeding

 

viburnum leaf beetle adults

 

  So, a recommendation for gardeners and landscapers relative to Viburnum nudum of DO NOT PLANT seems eminently reasonable, right?  

  Perhaps. To my mind, though, let us pause a moment to take a look at some caveats in the Cornell list:

  “This is a preliminary list compiled by Dr. Paul Weston, Woody Plant Entomologist, Cornell University. It reflects our experiences so far. Just because a species is listed as most resistant doesn't mean that it won't be infested.”

I   do not doubt the list, but in addition I want to suggest a very important general caveat relative to list utilization: DO NOT ALWAYS TAKE LISTS TO WHAT MIGHT SEEM THEIR LOGICAL CONCLUSION. This is not to say that any given list is not relevant or even the ruling factor that we should use. It is not to say that Viburnum nudum is not highly susceptible. But, for example, does this list actually mean we should not plant Viburnum nudum?

  Why do I say this?  Let us listen to Paul Snyder, horticulturist at Secrest Arboretum:

  “I haven’t observed any feeding on V. nudum at Secrest. This year we had moderate infestations on V. trilobum and V. dentatum {also on Cornell’s highly susceptible list}, all planted in close proximity to V. nudum. Moreover, I haven’t observed any ovipositing on this year’s growth.”

  This fits with my admittedly anecdotal observations over the past few years. Viburnum leaf beetle has been at Secrest for a number of years, but so has V. nudum. Additionally, at the Bent Ladder Cidery and Winery just several houses down the road from me in northern Wayne County, V. nudum is thriving and showing no damage. In fact the lead image in this alert is from there. Yet, in past years I have lost Viburnum dentatum in my yard to viburnum leaf beetle (though I was famously wrong, as Erik Draper has pointed out repeatedly, in my thinking early on that this insect was not really an actual killer).

  So, what can be the cause of these disparities be? Here are a few thoughts:

  1. Possibly VLB will eventually catch up with V, nudum at Secrest and everywhere else, and it just has not happened yet at these locations.
  2. Maybe it is about population numbers. Perhaps there are just not enough VLB here.
  3. Is it possible that once the first wave comes through and natural enemies emerge, a “highly susceptible species” may not be killed or heavily damaged – or be unworthy of its listing in a “preliminary list”?

 

green stinkbug predation on viburnum leaf beetle

 

  Note above: a green stink bug nymph going all predatory on a viburnum leaf beetle at Secrest.

  4. Maybe there is variability among V. nudum cultivars. 

  I think these are interesting issues relative to information utilization from lists. Maybe V. nudum is doomed and should not be planted, and it certainly at least deserves some reservations regarding its use, but I am not sure that this adaptable and beautiful native shrub should be cast out of our landscape designs. Perhaps I am channeling my inner Peter Smithers who said: “I consider every plant hardy {and other characteristics } until I have killed it myself”.

 

viburnum leaf beetle feeding

 

viburnum nudum foliage