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Hellebore black death is a serious disease of hellebores, probably caused by the virus Helleborus net necrosis virus (HeNNV), where plants become stunted, deformed and marked by black streaks and netting patterns.
Hellebore black death
The disease known colloquially among hellebore growers as ‘black death’ causes stunting, distortion and black streaking and netting patterns on the leaves. It is probably caused by a virus called Helleborus net necrosis virus (HeNNV).
In the UK, the most seriously affected hellebore is Helleborus × hybridus (syn. H. orientalis) but similar symptoms have been seen in other species. New damage can be expected from mid-spring.
You may see the following symptoms:
Symptoms not to be confused with general blackening caused by Botrytis cinerea or leaf spotting caused by Microsphaeropsis hellebori.
There are no chemical controls for plant virus infections.
Control of aphid vectors is not feasible with the products available to amateur gardeners because these are non-persistent and would need to be applied at unrealistically short intervals to give any protection against the arrival of winged aphids.
This disease has been recognised for about two decades in the UK, but is becoming progressively more serious. It is also known from mainland Europe and North America. A virus called Helleborus net necrosis virus (HeNNV) is associated with the disease and believed to be the cause. The virus is thought to be transmitted by the hellebore aphid, Macrosiphum hellebori. However, conclusive evidence for both suspicions is still lacking.
Aphids transmit viruses by feeding on the sap of plants with virus infection, and thus contaminating their mouthparts with virus particles. When they fly to healthy plants and begin to feed, they then infect the plant with virus. Seriously infected plants are so stunted they are unlikely to be attractive to aphids and the most dangerous plants are probably those that are still lightly infected and suitable for aphid feeding.
Hellebore leaf miner
Hellebore leaf spot
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