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Common Hellebore Diseases – How To Treat Sick Hellebore Plants

Common Hellebore Diseases – How To Treat Sick Hellebore Plants


By: Darcy Larum, Landscape Designer

Hellebore plants, sometimes referred to as Christmas rose or Lenten rose because of their late winter or early summer blooms, are usually resistant to pests and diseases. Deer and rabbits also rarely bother hellebore plants because of their toxicity. However, the term “resistant” does not mean that hellebore is immune from experiencing problems. Read on to learn more about the diseases of hellebore.

Common Hellebore Problems

Hellebore diseases are not a common occurrence. However, in recent years a new hellebore viral disease known as Hellebore Black Death has been on the rise. Though scientists are still studying this new disease, it has been determined to be caused by a virus known as Helleborus net necrosis virus, or HeNNV for short.

Symptoms of Hellebore Black Death are stunted or deformed growth, black lesions or rings on plants tissues, and black streaking on the foliage. This disease is most prevalent in spring to midsummer when warm, damp weather conditions provide an ideal environment for disease growth.

Because hellebore plants prefer shade, they can be prone to fungal diseases which frequently happen in damp, shady locations with limited air circulation. Two of the most common fungal diseases of hellebore are leaf spot and downy mildew.

Downy mildew is a fungal disease that infects a wide array of plants. Its symptoms are a white or gray powdery coating on leaves, stems, and flowers, which may develop into yellow spots on the foliage as the disease progresses.

Hellebore leaf spot is caused by the fungus Microsphaeropsis hellebori. Its symptoms are black to brown spots on the foliage and stems and rotted looking flower buds.

Treating Diseases of Hellebore Plants

Because Hellebore Black Death is a viral disease, there is no cure or treatment. Infected plants should be dug up and destroyed to prevent the spread of this harmful disease.

Once infected, fungal hellebore diseases can be hard to treat. Preventative measures work better at controlling fungal diseases than treating plants that are already infected.

Hellebore plants have low water needs once established, so preventing fungal diseases can be as simple as watering less frequently and watering hellebore plants only at their root zone, without allowing water to splash back up onto the foliage.

Preventative fungicides can also be used early in the growing season to reduce fungal infections. Most importantly though, hellebore plants should be properly spaced from each other and other plants to provide adequate air circulation around all aerial parts of the plant. Overcrowding can give fungal diseases the dark, damp conditions in which they love to grow.

Overcrowding also leads to the spread of fungal diseases from the foliage of one plant rubbing against the foliage of another. It is also always important to clean up garden debris and waste to control the spread of disease.

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Read more about Hellebore


Hellebore Flowers Offer Beautiful Late-Winter Blooms

  • Common name: Hybrid Lenten rose
  • Zones: 4 to 9 evergreen in 6 to 9
  • Bloom time: February-May
  • Bloom size: 2 to 3 1/2”
  • Height/Spread: 18 to 24” tall and 24” wide
  • Site: Partial shade, well-draining soil
  • Characteristics: Low-maintenance, deer-resistant

Hybrid hellebores get their common name, Lenten rose, from the rose-like flowers that appear in early spring around the Christian observance of Lent. The “blooms” (which are actually sepals that protect the true flowers) last for several months, from February until May, and the foliage is evergreen in all but the coldest regions.


Helleborus-Black Death

The most common symptom is blackened leaf veins.

OSU Plant Clinic image, 2015.

Black streaks may occur as lines and, when severe, are associated with distortion and stunting of affected plant parts.

OSU Plant Clinic image, 2015.

Symptoms include blackened leaf veins, dark brown to black streaks on petioles and black streaks on flower bracts.

OSU Plant Clinic image, 2015.

Cause 'Black death' has been reported in a number of states in the Western and Eastern United States as well as other countries. Although the cause of 'black death' has not been determined definitively, evidence points to a virus as the probable causal agent, specifically a Carlavirus tentatively assigned the name Hellebores net necrosis virus (HeNNV). HeNNV is genetically distinct from other viruses detected in hellebores such as Hellebores mosaic virus , Cucumber mosaic virus , Tomato spotted wilt virus and Chrysanthemum virus B. None of these other viruses have been associated consistently with 'black death' symptoms. HeNNV is serologically related to other Carlaviruses including Hellebores mosaic virus . HeNNV has been detected in the pollen of symptomatic flowering plants, but little is known about the potential for pollen transmission of this virus. Symptomless infection may play a significant role in widespread dissemination of the 'black death' causal agent.

A limited number of aphid species have been demonstrated to colonize hellebores, one or more of which may serve as vectors of the Carlavirus. The hellebores aphid ( Macrosiphum hellebori ) has been recovered more frequently than other aphids on symptomatic hellebores plants in the Pacific Northwest, but this aphid remains to be verified as the vector of HeNNV. The crescent-marked lily aphid ( Aulacorthum circumflexum ) and the violet aphid ( Myzus ornatus ) have also been found to colonize hellebores.

Symptoms of 'black death' have been reported primarily on the various cultivars or hybrids known as Helleborus x hybridus (formerly H. orientalis ). Little is known about the susceptibility of other hellebores species, but symptoms have not been observed on H. niger or H. argutifolius .

Symptoms Symptoms typically develop on well-established (older) plants, particularly on newly emerging foliage and on flowers (usually in mid-winter or early spring). A variety of symptoms have been observed in association with 'black death,' the most common including blackened leaf veins dark brown to black streaks on petioles black streaks on flower bracts and stunted, brittle, brown to black new growth. Black streaks may occur as ring spots or lines and, when severe, are associated with distortion and stunting of affected plant parts. Vein marking initially appears as light-colored thin lines but progresses rapidly. Infected plants are severely stunted. Depending on the virus isolate and hybrid line, the plants may linger in poor health for several seasons, or may die within weeks. Plants may be infected for 1.5 or more years prior to developing symptoms. Symptomatic plants do not recover. In the early stages of infection, the symptoms of 'black death' can be confused with leaf spotting caused by Botrytis , Coniothyrium , or Phyllosticta .

Symptoms of other virus problems include line patterns in the foliage (TSWV), mottling and rugose foliage (CMV).

Cultural control Control tactics are based on the likelihood that HeNNV causes 'black death' by means of systemic infection.

  • Purchase clean stock.
  • Growers should dig up and destroy symptomatic plants.
  • Control of aphids may help prevent spread of the causal agent of 'black death.' See the PNW Insect Management Handbook for details.

References Eastwell, K.C., du Toit, L.J., and Druffel, K.L. 2009. Helleborus net necrosis virus: A new Carlavirus associated with 'black death' of Helleborus spp. Plant Disease 93:332-338.

Koenig, R. 1985. Recently discovered virus or virus-like diseases of ornamentals and their epidemiological significance. Acta Horticulturae 164:21-31.


The Darker Side of Hellebore

Photo credit: Wikimedia Commons

While hellebore’s herbal history isn’t exactly comforting, its magical history is downright disturbing. Like so many of the primary herbs of legend, hellebore is downright scary at times.

It was said that medieval witches harvested hellebore on moonless nights, facing the east in defiance instead of supplication. Unlike Pliny, they cursed the coming dawn and spat on the ground as they brought forth the root. Then, they used it to curse and control those around them.

In folklore, hellebore is often used to call forth demons and curse enemies. It was particularly known to curse food and fields. Furthermore, neighbors with evil intentions sprinkled hellebore on wheat or vegetable gardens to make the harvest toxic or foul-tasting.

Flying Ointment

Old world witches were famous for their flying ointment. They rubbed a salve of herbs and rendered fat over themselves and then took off flying in the air. Hellebore features prominently in all of these recipes, alongside belladonna. Both herbs have a reputation for disrupting heartbeats and causing hallucinations.

Who knows if medieval witches ever actually flew, or if they only believed they did so because of the herbs’ hallucinogenic effects? Either way, flying ointment was a dangerous high and hellebore played a significant role in its makeup.

Invisibility

Borkia / Pixabay

Hellebore’s other primary magical use was as an invisibility powder. Witches ground it into a powder and then walked on it to make themselves invisible. Sounds like a helpful skill to have if you’re poisoning crops or flying through the air.

This plant isn’t all darkness and evil. It’s occasionally used in protections spells as well. But for the most part, it was cultivated and used in dangerous ways for malicious purposes. It’s a witchy, spooky, and dangerous plant to work with. But hellebore’s dark past makes it a delightful addition to a gothic garden.

If you’re hoping to create a darkly themed garden, whether it’s a witch’s garden, a poisoner’s garden, a medieval garden, or a goth garden, hellebore’s magical history and folklore make it an ideal addition.

The Language of Hellebore

Kapa65 / Pixabay

In the Victorian language of flowers hellebore has an interesting dual meaning. It primarily refers to a scandal, which fits well with the plant’s dangerous history and links to both witchcraft and insanity. But, hellebore has another meaning that offers a positive spin on any situation.

Hellebore can mean hope as well. After all, this deadly plant blossoms from beneath the snow. It blooms in dark winter days and reminds us all that spring is on the way. Hope fits the hellebore plant perfectly. Like so many of us, this uniquely beautiful plant has a lot of regrets in its past.

But maybe that’s why hellebore continues to have a home in our gardens. We won’t be using it to curse our neighbors or poison a town. Instead, we use it to find hope again in the darkness. Watching hellebore blossom in the snow, we feel that within each of us lives “an invincible summer..no matter how hard the world pushes against [us], within [us all] there’s something stronger—something better, pushing right back.”


Watch the video: Hellebore Care Guide