A number of years ago, I wrote an article warning of looming doom and gloom. It was a report on the relatively new disease attacking hellebores ominously called Black Death. Or to be scientifically correct: Helleborus net necrosis virus, HeNNV for short.
In the winter of 2015–2016 I had come across an article by the Royal Horticultural Society about this viral disease. No date on the article but further research revealed this virus was first declared in the United Kingdom and Continental Europe in the 1990s.
I also found another reference article noting there were a few hellebores that tested positive for HeNNV in a nursery somewhere in Washington state in the year 2000. This was the only mention I could find of the virus in North America and it did not give a specific location in Washington.
New Zealand identified the virus in the Waikato region in 2009 where some hellebores in a home garden were exhibiting black streaks on their leaves and stems. No mention of whether these hellebores had been imported from overseas or if the virus “just appeared.”
But six years ago, when researching the initial article, I could not find any mention of Black Death anywhere in Canada. Fast forward to present day and a fresh, exhaustive search has still not turned up any mention of this viral disease in our country. Good news for now, but will it always remain so? As we have learned with COVID, viruses do have a habit of getting around.
So far, scientists have not been able to determine how this virus developed in the first place but they do know it is specific to hellebores. And it usually develops in older plants; not so much in young plants.
When it comes to the garden, I try to be proactive… getting ahead of any potential problem, if I can. Part of that philosophy is knowing what may be coming, when it may come, and what to look for.
Remember those little white pupae I wrote about in a June 2021 column that turned out to be black vine weevils when they emerged? I now keep a watchful eye for them when I am moving plants because those pupae are typically amongst plant roots. (The ones I found just happened to be nestled in the roots of a hosta.)
This time of year, I am keeping a close watch on my hellebores for any telltale signs of HeNNV.
One symptom to watch for is any black- or brown-coloured new growth that is stunted and brittle-looking. Also, keep an eye on older leaves that may develop black streaks along the veins, or any stems with black or dark brown streaks, or black streaking on any of the flower bracts.
But do not be fooled! Black Death has been known to develop a pattern of rings, rather than streaks, which can confuse a gardener into thinking their plant is afflicted with the much less deadly disease, black spot. Regardless of which disease is causing the black, or dark brown, spots, promptly remove infected leaves and destroy them. If the streaking is spreading, dig up the plant and destroy it.
Over the years, it has been determined some hellebore species and cultivars are more susceptible than others to HeNNV. Most vulnerable seem to be Helleborus x hybridus and H. orientalis, along with their named cultivars. Less susceptible species are Helleborus niger and H. argutifolius.
Forewarned is forearmed, I always say!
Special note: I will be offering my workshops starting in late February. The list and details are on my website at duchessofdirt.ca.
Leslie Cox co-owns Growing Concern Cottage Garden in Black Creek. Her website is at www.duchessofdirt.ca