Viburnum is a genus of over 150 species of deciduous and evergreen perennials that feature showy flowers and attractive foliage, many of which are native to North America.
Most species are woody shrubs, though some have a spreading growth habit, and others can be pruned into a tree-like form.
These versatile, low-maintenance plants are easy to grow and – depending on the species and growing zone – will thrive in shady locations or full sun.
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In our guide to growing viburnum, we cover how to cultivate these plants in your landscape.
In this article, we provide an overview of the major diseases that may affect viburnum, most of which are treatable, and we explain how to control them.
Fortunately, viburnum is generally resistant to most diseases. Infected plants typically have been weakened by improper care or are in poor health otherwise.
Growing these shrubs in full sun will help to prevent many of these diseases, which typically occur in damp, moist conditions.
If the plant has grown very densely, the interior may retain moisture. Pruning the branches in the center of the plant can help to increase airflow and prevent a build up of humidity.
Also remove any plant material that falls to the ground, since it may harbor disease-causing organisms.
If, in spite of your best efforts, your shrub appears to have come down with symptoms of a disease, it’s likely to be caused by one of the following six conditions:
The arrowwood viburnum is a popular landscape shrub prized for its durability and multi-season appeal. But despite their hardy nature, these shrubs can still fall victim to a few troublesome diseases. Learning how to identify and treat common viburnum diseases is key to preserving the health and beauty of these garden favorites.
Below we cover the most prevalent infections you may encounter and provide integrated disease management tips
Anthracnose
Caused by: Elsinoë viburni fungus
Symptoms Small, round brown spots on emerging leaves in spring Spots enlarge and coalesce into large dead patches Infected leaves curl, wither and drop. Dieback of twigs may occur.
Conditions Warm, humid, wet weather. Common on crowded, stressed shrubs with poor air circulation
Treatment:
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Improve air flow through correct spacing and selective thinning.
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Prune out infected branches well below symptoms.
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Rake and dispose of fallen debris promptly.
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Apply fungicide sprays containing chlorothalonil, myclobutanil or propiconazole at bud break. Repeat every 7-14 days through spring.
Bacterial Leaf Scorch
Caused by: Xylella fastidiosa bacterium
Symptoms: Leaf margins scorch and turn reddish-brown. Scattered dead areas form between leaf veins. Leaves droop, curl and drop. Dieback of branches may occur.
Conditions: Spread by sap-feeding insects like leafhoppers. Favored by prolonged hot, dry periods.
Treatment:
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Improve plant vigor through proper watering, mulching and avoiding excess fertilizer.
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Apply broad spectrum insecticide sprays to control leafhopper vectors.
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Prune out infected branches, disinfecting tools between cuts.
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Remove susceptible viburnums growing near infected plants.
Powdery Mildew
Caused by: Erysiphe fungi
Symptoms: White to gray powdery coating over leaves and shoots. Infected leaves yellow, curl and drop. Dieback occurs in severe cases.
Conditions: Thrives in shady, crowded, humid conditions with poor air flow.
Treatment:
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Prune for open structure and good light penetration.
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Water at base, avoid wetting foliage.
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Apply fungicides like myclobutanil, propiconazole or neem oil at first sign. Repeat every 7-14 days.
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Rake and remove fallen leaves to reduce spore levels.
Root Rot
Caused by: Phytophthora fungus
Symptoms: Stunted growth, leaf wilt, dieback of shoots and branches. Roots turn brown and mushy. Sudden plant collapse.
Conditions: Wet, poorly drained soils. Spread by contaminated garden tools and water.
Treatment:
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Improve drainage and avoid over-watering.
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Disinfect tools after each use.
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Apply fungicide drench containing mefenoxam. Repeat 2-4 times annually.
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Severely infected plants should be removed and destroyed.
Rust
Caused by: Pucciniastrum viburni fungus
Symptoms: Yellow/white lesions on upper leaf surfaces. Corresponding orange/brown spore pustules erupting on leaf undersides. Heavy infections lead to leaf drop.
Conditions: Cool, moist weather. Spreads via wind and rain splash.
Treatment:
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Rake and dispose of fallen leaves to reduce spore levels.
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Apply fungicides containing myclobutanil, propiconazole, or chlorothalonil at first signs.
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Improve air circulation through correct spacing and pruning.
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Avoid overhead watering.
Prevention Is the Best Medicine
While treatment options exist for many viburnum diseases, prevention is always the best solution. Support robust shrub health through proper care and smart practices:
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Select disease-resistant Viburnum varieties like ‘Blue Muffin’ and ‘Morton’.
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Give viburnum optimal growing conditions – fertile, well-drained soil and appropriate sun exposure.
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Prune annually to improve air flow and light penetration into the canopy.
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Water appropriately at soil level – avoid wetting foliage.
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Apply an organic mulch layer to conserve moisture and discourage splash.
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Remove nearby weeds and diseased plants that may harbor infections.
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Disinfect tools regularly with bleach solution (1 part bleach to 4 parts water).
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Clean up and dispose of fallen leaves/debris promptly to reduce spore levels.
By correctly identifying and treating any diseases early, plus consistently providing good cultural care, you can help keep your arrowwood viburnum resilient, healthy and thriving for years to come.
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Algal Leaf Spot
As its name indicates, this disease causes an infection that shows symptoms on the leaves. The spots start out small and pale green before becoming reddish or light brown. They often have feathered edges and look like they are slightly raised.
Cool and moist conditions favor the development of algal leaf spot. Wind and splashing rain will spread this type of algae to nearby foliage.
The organism that causes it, a type of algae known as Cephaleuros virescens, overwinters in the leaf spots, ready to strike again in springtime.
You can control algal leaf spot with copper fungicide, such as this one from Bonide that’s available from Arbico Organics.
Treat your viburnums when you first see the symptoms, then repeat every 10 to 14 days until the disease is under control.
Armillaria Root Rot
Unfortunately, species of Armillaria (the honey mushroom) are found in soils throughout the world, and may cause fatal infections on a variety of trees and shrubs, including viburnum.
You may have no idea that your shrub is infected until it suddenly dies. Symptoms include yellowing of the leaves and stunted growth.
You can observe signs of the presence of this fungus as a white mat if you peel back the bark near the bottom of the shrub. Sometimes there will be stringy black growths on the roots or the soil surrounding your plant that are known as rhizomorphs or shoestrings.
There is no cure for this disease, and if you discover that your viburnum has a severe infection, you should immediately dig it up and destroy it in the trash, not on your compost pile.
Try and remove as many roots as you can and destroy those, too. This will help to prevent the fungus from remaining in the soil and infecting other plants.
In addition, you should remove the soil from around the root zone and dispose of it.
You will not be able to grow viburnum in the same area once the soil has become infected.
However, healthy plants are less likely to contract this disease, so make sure the soil drains well, fertilize properly, and provide additional water during periods of drought.
This fungal infection is serious, but fortunately it only afflicts shrubs that are already in poor health.
Your viburnum will be the most susceptible if it’s drought stressed, so be sure to provide additional irrigation during dry spells.
Areas of the shrub that have been pruned or that have damaged bark are also vulnerable to invasion by this fungus. Healthy plants will generally ward off such infections, but they can spread in unhealthy ones.
The first indication of this disease is leaves that wilt and die.
Next, the branches die. They will be covered with black or dark brown pimple-like fruiting fungal structures. If you look under the bark, the wood will be dark brown.
The afflicted areas will eventually become sunken, causing cankers to form. The cankers start out small, but they can grow together to form larger ones that can girdle the affected trunk or branch. This prevents water from moving throughout the plant.
Areas with cankers may fail to grow leaves the next spring.
Prune back the branches that are infected. Cut them all the way back to the green healthy wood, and sterilize your pruning shears between cuts.
If you have to prune an entire branch, cut just outside of the branch collar and do not make the cut flush with the trunk.
Be sure to destroy the material you pruned, since it contains fungal spores that could spread.
If you have mulched your shrub, it will be more resistant to mechanical injury from lawn mowers and weed wackers. Apply two to four inches of leaf mold, bark, or pine needles. Do not pile the mulch up against the trunk.
This is a disease that doesn’t kill its host, but it can be debilitating on viburnum.
Downy mildew is caused by Plasmopara viburni, and it is typically a problem when the weather is wet in the spring and moisture builds up on the leaves.
Symptoms include angular spots between the leaf veins that grow larger and cause the leaves to redden and turn brown before they shrivel up and die. The underside of the leaves will be covered in white fungal growth.
You can take measures to prevent this disease by raking up and destroying any infected leaves. It is particularly important to do this when the leaves fall to the ground in the autumn. Any diseased leaves that remain on the ground can cause infections when the rain splashes the spores to the new growth.
Do your best to keep the leaves dry. For example, avoid using overhead irrigation, and water only at the base of the shrub.
Prune any overhanging tree limbs or adjacent shrubs that might be growing into your plant, causing a damp, humid environment.
If you observe this disease, apply a copper fungicide as soon as possible. However, be sure to avoid those containing sulfur, since they can be toxic to viburnum.
Problems with Viburnum
FAQ
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