by Erin Marissa Russell
When you raise hellebores, the last thing you want is to lose your carefully tended plants to disease midway through the growing season. That’s why we’ve prepared this guide that will arm you with the knowledge you need to recognize hellebore flower diseases early and take action to fight against them—and keep them out of your garden for good.
Defend Your Hellebores Against Downy Mildew Fungus
The spores that spread downy mildew fungus among plants proliferate when weather is cool and wet with high humidity. Plants that stay wet are especially susceptible. This disease can spread from plant to plant through wind, splashes of water, or by hitching a ride on traveling insects.
If downy mildew becomes a problem in your garden, you’ll recognize the telltale white, brown, purple, or grayish powder coating leaves, stems, and flowers on your impacted plants. Downy mildew fungus may also manifest as yellowish patches on plant leaves. As the disease progresses, plants may drop blooms or foliage, fall victim to other infections, and become weak. Without treatment, downy mildew can kill plants, so it’s important to take action. Fungicide can be successful if you use it early enough, but there are other steps gardeners can take to battle downy mildew as well.
First, make the environment less habitable for downy mildew by watering carefully. Make sure not to over-hydrate your plants, and water them from the base to minimize wetness remaining in foliage. You may rearrange your garden to maximize spacing between plants and increase air circulation. As always, make sure that the soil where plants are growing offers plenty of drainage. Mulch can keep air moving while also preventing the spread of disease when rainfall splashes soil through the garden.
Protect Plants Against Hellebore Black Death
Not all of the diseases that cause your hellebores to turn black fall into the category of the hellebore black death virus. Black death tends to affect mature plants, blackening new foliage and flowers along the plants’ vein systems. You may also notice blackened new growth that isn’t developing as it should and dark areas, jagged streaks, or ring spots on petioles and bracts.
To tackle hellebore black death in your garden, you’ll need to remove all affected foliage carefully. Because black death is contagious, be sure to clean your tools before and after use. You’ll also need to bag up all the plant matter you remove and dispose of it properly. After this treatment, if a hellebore continues to display black death on new growth, the entire plant must be removed from the garden. If you just can’t shake the hold of black death in your garden, consider attacking aphids, which are known to spread the disease.
Fight Against Leaf Spot and Black Spot Fungal Disease
Leaf spot and black spot are fungal diseases that are known for spreading quickly, which means gardeners should know the signs and stay vigilant against them. These fungi tends to attack in late winter when hellebores are just about to flower. Leaf spot disease targets new growth especially, affixing its spores to the undersides of hellebore leaves and stems. Until leaf spot and black spot are treated, these spores will continue to proliferate and spread the disease as hellebores mature.
Affected plants may display yellowing leaves, damaged blooms, or patches and round spots of brown and black on foliage. The disease will start small, the damaged area spreading until plants lose tissue, causing holes in leaves or collapsed stems.
To treat a leaf spot or black spot epidemic, remove any hellebores that are showing signs of the disease. If the plants have begun to drop leaves, pick the leaves up and dispose of them with the affected plants. Be sure to clean your gardening tools before and after this task, and use clean practices when handling the diseased plant matter, to avoid spreading the fungus throughout your garden.
To strengthen your hellebores against leaf spot or black spot, there are preventive measures you can take as well. Applying a fungicide in December or January that contains mancozeb or myclobutanil, especially targeting the bases of plants, will help hellebores flourish. Pruning damaged or dead foliage throughout the year, with a final major pruning in autumn, goes a long way toward keeping plants healthy.
You can also guard against these fungal diseases by picking up dropped leaves throughout the season and disposing of them carefully. Finally, ensuring that plants are spaced widely enough to allow plenty of air circulation will make it harder for leaf spot fungus to take hold.
As you can see, there’s no reason to let your hellebore plants fall prey to hellebore black death, downy mildew, and black spot or leaf spot fungus. Often, an ounce of prevention is worth a pound of cure, so simply knowing how to keep your plants healthy from the start can ensure you never deal with these diseases. However, should a hellebore epidemic break out in your garden, now you know exactly how to fight back.
Want to learn more about hellebore diseases?
Extension covers Hellebore Diseases
Dave’s Garden covers Hellebore Leaf Spot
The Garden of Eaden covers Pests and Diseases of Hellebores
Helleborus covers Pests and Diseases
Northwest Garden Nursery covers Hellebore Care Instructions
Pine Knot Farms covers Caring for Hellebores
Pacific Northwest Pest Management Handbooks covers Helleborus Plant Diseases
Royal Horticultural Society covers Hellebore Black Death
Royal Horticultural Society covers Hellebore Leaf Spot
The Seattle Times covers Lenten Rose
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