5 Common Hellebore Diseases: ID and Treatment

In addition to their lovely late winter blooms and handsome foliage, hellebores are relatively carefree perennials. While usually problem-free, they are susceptible to certain diseases, some recoverable and some serious. Join gardening expert Katherine Rowe in a look at common diseases for hellebores and how to treat and prevent them.

Close-up of white Helleborus flowers with five smooth petals, a pale yellow-green center, and fine stamens.

Contents

Hellebores, with their cupped blooms that grace the late winter landscape, are favorites in the woodland border, shaded bed, and container arrangement. Their elegant flowers in shades from blush to scarlet to near-black complement their attractive palmate leaves, mostly evergreen. 

With the right cultural conditions, the ornamental perennial is an easy-care, long-lasting garden performer. They slowly colonize to form a handsome groundcover.

While hellebores are mostly trouble-free, they are susceptible to common fungal diseases and viruses. Early detection helps them recover from infections and prevents the spread. Here, we’ll explore common diseases among the beloved blooms, as well as how to treat and prevent them.

Setting Hellebores Up For Success

A grouping of Helleborus plants featuring bell-shaped flowers in shades of pink, cream, and light green, growing upright near a tree trunk.
They grow best beneath a deciduous canopy that offers sunlight in winter and dappled shade in summer.

Hellebores are in the buttercup family, Ranunculaceae, with about 20 species native to Europe and Asia. Helleborus orientalis (Lenten rose) and their hybrids (x hybridus), and the earlier-blooming H. niger (Christmas rose), are long-lived, some reaching 20 years or more. There are those with tall stems, like H. argutifolius (holly-leaved) and H. foetidus, stinking hellebore. Heavily hybridized for vigor and bloom density, hellebores boast a long bloom time in various colors with single or double flowers. 

Providing optimal growing conditions builds sturdy root systems and boosts resiliency against pests and diseases. Hellebores grow best beneath a deciduous canopy that offers sunlight in winter and dappled shade in summer. They prefer fertile, loamy, or sandy soils with good drainage. The low-maintenance perennials are drought tolerant once established but do best with supplemental water during prolonged dry spells.

A gorgeous addition planted en masse under trees, as a border, or naturalized ground cover, hellebore pairs beautifully with other shade-loving plants like fern, heuchera, epimedium, acanthus, solomon’s seal, and hosta. 

Leaf Spot

The leaves exhibit dark, water-soaked spots that turn brown, surrounded by yellow halos, giving them a distressed appearance.
Brown, dead spots, round and patchy, increase in size and number and spread across leaves and stems.

Leaf spot is a common fungal infection that grows on leaf surfaces. Hellebores have their own specific fungus to watch for, Microsphaeropsis hellebori. Brown, dead spots, round and patchy, increase in size and number and spread across leaves and stems, causing them to blacken. As the dead tissue falls away, leaves become ragged, and stems collapse. Spots may also appear on petals and buds, causing wilting and failure to open.

The fungus develops in warm conditions from spring to fall but it is most likely to appear with spring’s new flush of growth. Any species may show signs; H. niger is highly susceptible.

The brown-black spots crop up when leaves stay wet from prolonged moisture from rain or overhead watering. 

Treatment

Early detection is the best control for leaf spot. Cut off diseased leaves and remove any that drop to avoid overwintering for the next season. Destroy or discard the impacted parts away from the garden to prevent spread, keeping them out of the compost pile. Sanitize pruners while moving between plants. An alcohol wipe or a dip in a 70% isopropyl alcohol solution is handy while working.

Prevention

Ample air circulation is the best defense against leaf spot. Also, water at the ground level rather than spraying the leaves to reduce damp conditions. Add a mulch layer to reduce soil splash during watering (and for other benefits like insulation, weed suppression, and moisture retention). Prune surrounding plants where appropriate to increase air circulation.

Hellebore Black Death

Close-up of Helleborus plants with wilted, darkened leaves and shriveled flower buds.
It shows black streaks and netting along leaf veins and margins, accompanied by yellow mottling.

The black death is as ominous as it sounds if you’re a hellebore. Helleborus net necrosis virus (HeNNV) shows black streaks and netting along leaf veins and margins, accompanied by yellow mottling. Growth may deform and stunt. Older specimens are the likeliest to exhibit signs with streaks on emerging new growth in late winter and spring. Symptoms become more pronounced as the season progresses.

The vector for the virus is the hellebore green aphid, Macrosiphum hellebore. This little pest can do big damage by spreading the pathogen as it feeds and flies from plant to plant.

Treatment

There’s no chemical control for this deadly virus. The best measure is to dig, remove, and destroy the infected specimen. This is the strongest course to prevent its spread to other lenten roses. If there’s a bright side, it’s that HeNNV only affects Helleborus; other garden plants are safe from its destruction. Sanitize any tools used in the removal.

Prevention

Scout for the hellebore aphid and any signs of early disease. Unfortunately, it’s unlikely that treating for aphids will prevent the virus, as the winged creatures move throughout the season.

But, if you notice aphid populations, treat them with a strong spray of water early in the day to dislodge the insects from leaves and stems. In severe outbreaks, a horticultural soap or oil like neem is effective. Follow label applications, as these affect beneficial insects, too.

For a well-rounded garden system, attract beneficials with a diversity of plants. Predators like lacewings and ladybugs feed on aphid populations as a means of natural pest control.

Crown and Root Rot

Close-up of green shoots sprouting from dark brown soil, surrounded by white, fuzzy fungal growth.
With crown rot, brown patches and rotting may appear where the leafy stems emerge just above the soil line.

Root rot and crown rot occur in humid environments and overly wet conditions. With root rot, the pathogen Phytophthora, among others, impacts feeder roots, which are unable to absorb water and nutrients. Signs of root rot include drought-stressed leaves that turn yellow and wilt. 

Check for rot by inspecting stems and roots slightly below the soil line. Rotting roots will be yellow or brown rather than a healthy white. They may even have a foul odor.

Crown rot occurs after prolonged saturation from rainfall or irrigation and intensifies with a lack of air circulation and poorly drained soils,

With crown rot, brown patches and rotting may appear where the leafy stems emerge just above the soil line. Brown or black lesions may occur.

Treatment

The best action is to remove and dispose of severely impacted plants. Removal prevents the fungus from spreading to other plants, and many garden favorites are susceptible to crown rot.

Reduce irrigation frequencies to allow oversaturated soils time to drain. Keep soil evenly moist but not soggy.

Prevention

The best way to prevent rot is to avoid overhead watering and saturated conditions. Water at the base, either by hand or with drip irrigation or soaker hoses. These deliver moisture to the roots without splashing foliage or harboring damp situations. Increase air circulation, especially in humid conditions.

Water deeply and increase the length of time between sessions if needed. Deep watering allows better absorption over frequent, shallow watering.

Botrytis

This disease is indicated by light grayish-brown watery spots on petals.

Botrytis cinerea is a blight (also called gray mold) indicated by light grayish-brown watery spots on petals. Leaves discolor, and brown spots and “fluffy mold” appear.

Botrytis thrives in the cool, damp conditions of spring and fall. It affects a wide range of plants, from ornamentals to food crops.

Treatment

Botrytis is an adaptable fungus that adjusts to fungicidal treatments. Use both organic foliar applications and added soil microbes to keep the spores from developing immunity.

Neem oil is effective early on, as is potassium bicarbonate. Use a powdered formula mixed with water as a regular spray treatment, Mycorrhiza and beneficial bacteria added to the soil are suitable countermeasures. Look for Trichoderma and Cladosporium to ward off botrytis.

Prevention

To avoid botrytis is to prevent lingering moisture. Take care not to overwater or overfertilize, which causes weak growth  and increases susceptibility.

Like crown and root rot, botrytis thrives in high-humidity with limited airflow. Proper spacing and watering that avoids wetting the leaves unnecessarily is a good defense. Remove fallen debris that can harbor spores.

Downy Mildew

A flowering plant with deep red buds and dark green leaves marked with round, grayish spots.
This disease causes grayish-white lesions on leaves and blooms.

Peronospora pulveracea, or downy mildew, causes grayish-white lesions on leaves and blooms. While it may do no damage, it can lead to death as it spreads and feeds on water within the leaves.

Spores spread on the wind, on infected plants or tools, or by splashing up from the soil via raindrops and irrigation. The spores begin on the leaves and spread, depleting energy and nutrition.

Leaves turn yellow, distort, and drop during severe infections. The fungus spreads quickly, and if left untreated, plants wither and eventually die. Fortunately, powdery mildew is treatable with early detection and doesn’t usually kill hellebores.

Treatment

Handpick and remove the leaves when feasible. Discard them, keeping them away from the compost pile.

For more extensive outbreaks, horticultural oils like neem can treat downy mildew early on. Organic elements in fungicides like copper may be effective. Follow application directions, as these treatments may impact beneficial insects that visit plants for nectar and pollen. Time of day is important in using products effectively.

Prevention

To avoid splashing water on the foliage, water at the base of the stems. Splashing transmits spores and fosters their ideal environment. Avoid overfertilizing, too – hellebores usually don’t need supplemental fertilizer. Too much nitrogen leads to weak, leafy growth susceptible to disease.

Remove old leaves on most hellebores as new leaves and flowers emerge to prevent the spread. Keep the leaves on those with stems, like stinking (H. foetidus) and holly-leaved (H. argutifolius), until after flowering.

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