by Leslie Cox; Monday; February 20, 2017

 

This is a warning to all lovers of hellebores…

Black Death is out there.

Scientists do not know a whole lot about this relatively new disease, but one thing they do know for certain…

There is no cure!

To back up a bit…Black Death has been identified as a viral disease which is species specific to hellebores. (“Species specific”, in this case, means Black Death only attacks plants in the Helleborus genus.)

So far, no one has been able to determine how this virus developed but it has been spreading further afield in the UK for more than twenty years now. And probably longer, as it would have taken a while for someone to pick up on the fact this disease was something new…and deadly.

More recently, Black Death has begun to show up in North America…thanks to global trade traffic. While reported incidences on this side of the pond are relatively few, to date, lovers and collectors of hellebores must be on the alert.

Black Death…or to give it its new botanical name, Hellebore net necrosis virus, (HeNNV for short)…usually begins as distortions on the new foliage which stunts the plant’s growth. Black streaks will start to appear on the leaves in early to mid-spring…generally following along the veins.

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 a less deadly hellebore disease called leaf spotting. This disease is caused by the fungus, Microsphaeropsis hellebore. Another disease, Botrytis cinerea…also less deadly than Black Death…causes general blackening on the hellebore leaves which could lead to a misdiagnosis by the gardener.

Regardless of which disease is causing the black, or dark brown, spots…or the general blackening…it would be wise to promptly remove infected leaves and destroy them. DO NOT PUT THEM IN YOUR COMPOST.

If your plant is indeed smitten with Black Death, the damage will become progressively worse as spring advances. Black streaks will start to develop on the stems and extend onto the flower petals.

Research on HeNNV is ongoing, with scientists focussing on how it is transmitted. Early suspicions place the fault on everyone’s pest scourge: the aphid. And they are pointing fingers at the species specific aphid, Macrosiphum hellebori…although any aphid is quite capable of carrying the lethal virus from one plant to the next.

Recommended control of Black Death is to dig up all infected plants and destroy them. It would also be wise to guard against aphid infestations by ensuring your plants are well nourished and cared for. Healthy specimens are far less likely to come under attack by pests.

 

Thanks to my friend, Sylvia Stone, for letting me photograph just some of the beautiful hellebores in her collection. My apologies for only including a “tasting” of her hellebores in this article. I promise more will be showcased in future blog postings.