Attack of the Killer Viburnum

No, this isn’t a review of a Grade B horror movie, although to my mind this shrub certainly could star in one if it had a mind to. It’s the same viburnum whose flowers were so attractive in May but whose evil nature revealed itself recently.

 

Perhaps I’d better start at the beginning. This shrub sits at the juncture of driveway, front walkway and garage. When I moved into the house in early November I made a mental note to cut it back in early spring because it had gotten much too tall and wide for the space allotted to it. This I did as soon as the snow disappeared, and reduced the shrub in size to about 5 ft high and wide. Nice and tidy, and I had a plethora of bare branches to dispose of. In fact, considering the amount of branches I removed, I was surprised that it eventually produced any flower clusters at all in May.

However, I recently noticed that the shrub had really gone to town in the new-growth department and if I didn’t want it to soon be as big as it had been last fall, I’d better get out the pruners again.

What I didn’t know was that this viburnum was armed and dangerous.

Now, I’ve grown viburnums before; my previous garden had Viburnum dentatum ‘Blue Muffin’ as well as V. dilatatum ‘Erie’ and ‘Michael Dodge’. I also had V. plicatum ‘Mariesii’ and the pink ‘Molly Schroder’ although they were ultimately despatched by Hurricane Sandy. All lovely shrubs which never displayed a hint of animosity toward me. However, this nefarious character who came with the Money Pit/Temporary Garden is another matter entirely.

The encounter began innocently enough: snipping some outer branches with my hand pruners. But in order to get to all the new tall central growths, I had to reach into the shrub itself and so a number of the multitude of leaves inevitably brushed against the sides of my face and neck, as well as the small amount of skin exposed between my (long) sleeve ends and glove cuffs.

I’d reached and cut for about two minutes before I felt anything, but suddenly it seemed as though a tiny needle was being stuck into one side of my neck. Thinking it was an insect, I instinctively brushed at the spot. It didn’t help. In less than a minute several areas of my face, neck and wrists felt as though millions of tiny red-hot knives were being stuck into them. What the….?!?!?!?!???

Stripping off my garden gloves, I dashed indoors and spent the next ten minutes at the nearest sink. After the pain subsided I returned to the scene of the crime and examined the shrub from a safe distance (i.e., with the zoom lens of my camera.) Apparently this plant has quite a bit of weaponry at its disposal.

 

The new growth is entirely covered in what looks like soft indumentum-like hairs. I don’t know if these are part of the arsenal and am not inclined to experiment by swiping it against my skin. I do know that when I pruned the shrub in early April all of the branches were woody and smooth.

 

The leaves actually have two secret weapons: their matte and almost invisibly hairy surfaces, and their very slightly serrated edges which are also edged with the deadly hairs as seen clearly in this backlit photo.

When I examined my pruning gloves (after donning a pair of disposable latex gloves, of course) they were covered with them. A thorough going-over of gloves, shirt and pants with a lint roller eventually removed them; I didn’t want to risk putting the items into the wash, in case their nasty effects might be chemical as well as structural in origin.

 

In any case, this is as far as I got with reducing the Killer Viburnum in size….not as much as I’d originally planned, but better than nothing.

Believing as I do in the tenet “Know thy enemy” I decided to sleuth out what species it is. The oldest leaves are 9” (about 23cm) long and 4” (10cm) at the widest point. Cornell University’s Dept of Agriculture has a handy interactive online viburnum identification guide (don’t be put off by the leaf beetle reference) which I was able to work through and determine that it is Viburnum x rhytidophylloides.

According to the Ohio State University horticultural site ts parentage is V. rhytidophyllum x V. lantana. Height is given as 12’x12’ “although sometimes larger” which I can well believe, and having a fairly rapid growth rate. Foliage description is spot on: dark green above while much paler white-green beneath……having a rough texture with sunken veins above, with prominently large veins beneath that have a reticulate branching pattern…. leaves are opposite, narrowly ovate to oblong, lightly serrated or entire… about 3 to 4 times as long as they are wide, and often in a tattered and ragged semi-evergreen state by early Winter [this is so true; it looks absolutely horrid]…. Fruits at first green, then transitioning to red, red-orange, or red-yellow by mid-Summer, then maturing to black in late August and early September [dead on, yet again]. The full description can be found here.

There are also two cultivars of this viburnum: ‘Willowwood’ which was developed in the late 1920s and ‘Allegheny’ dating from the 1960s. Supposedly the former tends to hold onto more of its leaves in winter, but the latter tends to produce more flowers/fruit. A good pictorial comparison of both (and to the leaves of the V. rhytidophyllum parent) can be found here at the University of Kentucky site.

August 2021 Update:

During the six years since this post first appeared, it has received a significant number of visits as the result of Google and Bing searches for ‘itchy viburnum’, ‘viburnum allergy’, ‘viburnum itch’ and similar phrases! Clearly, I was not the only victim of this plant and/or its parent, Viburnum rhytidophyllum, sometimes called the Leatherleaf Viburnum. Further research has confirmed that it is indeed that parent plant which is responsible for the discomfort associated with its offspring, V. x rhytidophylloides ….my ‘killer viburnum.’

A few web sites do acknowledge the allergenic capabilities of the parent plant, although the hybrid is rarely mentioned. The database entry for V. rhytidophyllum on Dave’s Garden does include, in the ‘Danger’ field, “Handling plant may cause skin irritation or allergic reaction”, and there are several discussion forum threads elsewhere in which people report experiences similar to mine from contact with that plant. But until now I have found no explanation of how it – and its’ hybrid offspring – manages to do what it does.

I found it, amazingly, on the website of a European manufacturer of microscopic equipment, in an October 2020 blog entry. The plant observed was V. rhytidophyllum but it seems that the relevant plant structure of its equally evil child in my garden is the same. Here is the science/biology behind the attack.

The Viburnum rhytidophyllum or Leatherleaf plant is…‘Hairy’; that is, occupied with stellate (star-shaped) non-glandular trichomes. Trichomes can have many functions like defence against harmful insects, humidity regulation and even a sensory function. …When handling Viburnum rhytidophyllum one should be careful because the hairs (stellate trichomes) sting. The hairs can be inhaled as fine dust during horticulture and cause itching, redness of the face, even memory problems and asthenia…

That certainly sounds like what quite a number of gardeners have reported. I had to look up asthenia; it is defined as “weakness; lack of energy and strength; loss of strength.”

What is absolutely fascinating is that the article also contains two microscope slides showing the culprit that causes gardeners such misery. Here is one of the slides but I highly recommend that you also look at the full-size version at this link for even greater detail, and/or the relatively short blog post itself, which is titled Viburnum’s annoying ‘hair’. The golden-yellow structures are the trichomes that cover the leaves and branches. It’s no wonder that contact or (yikes!) inhalation of these can produce a nasty reaction!

Although the slide is quite beautiful, resembling a piece of stained glass, it also makes clear how these very tiny structural features can be so very effective at causing a world of hurt! I suspect that the only way to safely handle or work near either V. rhytidophyllum or V. x rhytidophylloides is to wear long sleeves, substantial gloves, and probably also a KN95 or N95 face mask to protect against inhalation. (I doubt that a basic blue surgical-style mask would suffice.)

In my opinion, nurseries should be more responsible in the advertising of these two viburnums than most of them currently are; and databases and botanic garden websites should mention, as Dave’s Garden does, the probability of adverse reactions upon contact.

By the way, you can find out what eventually happened to my Killer Viburnum here!