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Toxicity

All helleborus plants are toxic. All parts of the helleborus plants are toxic and should be handled with care. . Hellebore poisoning is rare, but it does occur.

Poisonings will occur through ingestion or handling. Hellebore plants should not be ingested. Poisoning cases are are most severe when the plants are eaten in large quantities. Symptoms of ingestion will include: burning of the mouth and throat, salivation, vomiting, abdominal cramping, diarrhea, nervous systems and possibly depression. Cardiac glycoside is one of the chemical responsible, and typically found in the roots of hellebores.Cardiac glycoside poisoning can be treated by administering atropine and activated charcoal. Lidocaine should be used for Helleborus viridis. High amounts of ranunculin and protoanemonin on the outside of the plant, and especially in the leaves and sap, will also contribute to symptoms after ingestion.

Dermatitis may also occur from handling the hellebore plants. This is typically caused by the ranunculin and protoanemonin found on the outside of the plant, including areas such as the leaves, stem, flower, and sap. The poison on the outside of the plant will cause irritation and burning sensations on the skin. When collecting seeds from hellebore plants it is recommended to wait for the pods to dry and shake them out into a container or onto the ground to collect. Attempts to remove the seeds by hand will expose skin to the toxins in the sap of the hellebore, which will increase the risk of harm to the skin. Small or minimal exposure to the toxins should only cause a mild irritation to the skin, and the affliction should only last for a few minutes. If the burning persists or intensifies, it is recommended to wash the affected areas thoroughly and go to the doctor.

Pests and Diseases

Animals and Insects

Hellebore plants are usually left alone by animals such as deer and rabbits due to the fact that the leaves of the plant produce poisonous alkaloids, making them distasteful to animals. The poisonous alkaloids have been known to sometimes bother gardeners with sensitive skin.

Phytomyza hellebori or more commonly known as the Hellebore leaf miner is a small fly that infests only the H. foetidus plants in the Hellebore family. The leaf miner fly digs tunnels into the leaves of the H. foetidus. The tunnels create brownish-black blotches on the plant. These will later turn into a nesting ground where the flies will lay their larvae in, which will turn the leaves a brownish-white along where the tunnels were dug. The larvae will start to eat the inside of the leaves in August, and damage will develop from the late summer to the early spring, with heavy attacks leaving the foliage disfigured by spring.

The plant is not greatly harmed during by the leaf miners and the damage done is tolerable to the plant. To control heavy infestations, the leaves can be removed during the winter months before the adult flies emerge and destroyed. Insecticides can be used with limited effectiveness in controlling larvae and fly populations in the plant. Insecticides may harm non-leaf miner flies if applied during the hellebore's flowering period.

Macrosiphum hellebori, more commonly known as Hellebore aphid or greenfly, is a sap feeding aphid that infests the flowers and foliage of hellebore plants. The whitish-green aphids are about 2-4mm long and form dense colonies on hellebores, coating them with a honeydew that can lead to the growth of sooty mold on the leaves and flowers of the hellebore. This species of aphid only affect hellebores and are most active in March and April when the hellebores are flowering and when few aphid predators are around, though they may infest during any time of the year.

Aphids will start their feeding from the outside flowers on the leaves and then move inwards and into the flower as the hellebore beings to open. The aphids will then move to feed on the inner parts of the plant as well as the young stems and shoots. As the population grows, the aphids will eventually eat the remaining parts of the plant, such as older leaves, for food.

Aphid infestations can be controlled through persistent squashing of the aphids manually, or by using insecticides. It is not recommended to spray flowering hellebores as it may harm the non-aphid pollinating insects.

Diseases

Botrytis cinerea or grey mold is a fungal disease that infects most ornamental plants. The fungus causes a decay of plant tissues and will grow fuzzy gray-brown mold over the decaying areas, such as the buds, leaves, and flowers. Parts of the plant may shrivel and die after exposure to the mold, particularly the flowers. Typically the fungus will only infect plants through an open wound or when the plant is under stress, however it has also been known to also infect plants in humid conditions. If the humidity is low the mold may be contained to discrete spots on the plant, but the mold has been known to spread rapidly in highly humid conditions. Grey mold can infect a plant at any time of the year and is not seasonally dependent. The fungus will form black seed like structures in the dead plant tissue to create its spores to help it survive when new host plants are scarce. The spores are spread through the air to new plants.

To treat the plant, remove the infected and dying leaves, buds and flowers immediately along with any other dead plant materials around the hellebore. Reduce the humidity around the plant by improving the ventilation and ensure the plants are not overcrowded.

Coniothyrium hellebori is a fungus that causes the most common fungal disease for helleborus species known as Hellebore black spot or leaf spot. The disease is most common not only in botanical and ornamental gardens, but also in hellebore nurseries as well. Visible symptoms include blackish-brown spots that often appear as rings on the leaf blade or at the margins of the leaf. The spots will continue to grow larger as the disease progresses, retaining an elliptical or circular shape and turning a dark brown or black color. The spots will grow until they have infect the whole leaf. Petioles and flowers can also be infected, but the disease is primarily seen in the leaves. The symptoms become visible in the spring and worsen with time.

The small black fruiting bodies which carry the spores, pycnidia are formed in the dead cells of the leaf spots. The spores are mainly spread by water, wind and wind-blown rain. The fungus have an ideal habitat to spread and grow at the final growth site for hellebore plants and if left untreated the spores will remain for many years. The most effective method against C. hellebori is to remove and destroy the infected leaves immediately to avoid reinfection the following spring.

Helleborus net necrosis virus (HeNNV) also know as Hellebore black death is an RNA virus that can cause serious disease in Hellebore plants by stunting or deforming the plant as it grows. The disease marks the leaves of the hellebores with black streaks, often following the veins of the leaf, and creating ring patterns. It can also mark the sepals and flowers with black spots or streaks, but it will not always do so. When symptoms are severe new leaves will have limited growth before dying off. The most seriously affected in the UK is Helleborus orientalis, but all hellebores are susceptible to the disease. The most effective method of treatment against black death is to dig up and destroy all infected plants immediately. Many viruses are not transmitted through seeds, so it is possible to raise new disease resistant plants this way.

Pseudomonas viridiflava is a bacteria that has been claimed to cause disease in hellebores in New Zealand, among other plants. The bacterial disease manifested on hellebore plants in the form of black leaf spots, necrosis petal, and stem lesions. The most popular ornamental and commercial crop grown in New Zealand is the Helleborus orientalis and it's hybrids, of which 90% of the H. orientalis in the Tauranga nursery contracted the disease after several days of moderate rainfall. The disease caused discoloration in the form of: black leaf spots on the plant that were circular and about 1.5-2mm in diameter, black stem lesions, and dry, grey to brown lesions with distinct margins on the flower petals. The symptoms were different from other leaf-spotting hellebore diseases, such as those caused by the fungus Coniothyrium and the bacteria Xanthomonas The case in New Zealand is the only reported case of P. viridiflava infecting hellebores so far, but on other plants P. viridiflava has been reported to also induce symptoms such as leaf rot, leaf blotch, stem necrosis and blossom blight.