Diseases Affecting Viburnum: Learn About Viburnum Disease Treatment


By: Bonnie L. Grant, Certified Urban Agriculturist

Viburnums have layered branches that are coated in spring with lacy, delicate and sometimes scented flowers. They are remarkably tough plants and suffer from few pest and insect issues. There are more than 150 species of Viburnum with many available for problem areas of the garden. Plants that are not well taken care of, however, can occasionally develop viburnum diseases, primarily fungal issues, especially if circulation is not provided.

Common Viburnum Diseases

Viburnum shrubs are very adaptable plants. That means they rarely have any disease issues. Common viburnum bush diseases encompass those caused by fungus, while other disease issues are rare. In most cases, correct siting of plants, adequate air circulation and good watering practices can prevent these soil or air borne problems. Plants under stress are most prone to lasting damage from these types of illnesses.

Foliage

The most prevalent diseases affecting viburnums are fungal diseases of the foliage.

  • Powdery mildew affects many types of plants, from ornamentals to vegetables. It is characterized by fine white dusty growth on the upper surfaces of leaves.
  • Downy mildew causes leaves to develop splotched areas which die and shrivel in spring. It is most common when the weather is wet.
  • Fungal leaf spots are caused by a different fungus, Cercospora or sometimes Anthracnose. Spots on leaves begin small but gradually develop. The area is angular and irregular and may be reddish to grayish brown. These tend to occur in warm, wet summer months.

The viburnum disease treatment for these types of plants is all the same. Avoid overhead watering, apply fungicide if the disease is rampant and destroy damaged leaf material.

Roots

One of the most damaging diseases of viburnum is Armillaria root rot, also known as shoestring root rot or mushroom root rot. This is another fungus, but it affects the roots of the plant and can lead to death. Initially, the leaves and stems of the plant will appear stunted, yellow and leaves may drop to the ground. As the disease works on, the roots of the bush will gradually get sicker and sicker. The process can take several years but eventually the tree will die.

It can be hard to diagnose, as symptoms mimic other stresses such as lack of water or poor care. The upper crown and roots of the plant will pinpoint the cause if examined, however, and white fungal growth will be visible under the bark. If the root system is diseased and making its way into the trunk, the plant cannot be saved. This is one of the most dangerous of the viburnum bush diseases.

Bark and branches

Botryosphaeria canker is a serious disease of viburnum and many other ornamentals. It is characterized by dead or wilted leaves. The fungus produces fruiting bodies that show up on bark and branches as brown to black, plump bumps. Bark becomes dark brown. The fungus gets into the plants through some injury and destroys the cambium. Cankers form, which girdle the tree, effectively cutting off nutrients and water movement.

Drought stressed bushes are mostly affected. Prune off affected material with sterilized pruners and provide consistent water and fertilizer over the season. There is no viburnum disease treatment for this ailment, but once the plant gains health, it can usually withstand the fungal attack.

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Viburnum is susceptible to several fungal leaf spot diseases including Cercospora, Phoma, Phyllosticta and Plasmopara viburni (downy mildew). Cercospora, Phoma and Phyllosticta leaf spot infections produce small angular spots with red to brown coloration on leaf tissue. As the diseases progress, the spots enlarge and merge. Downy mildew symptoms appear on the lower side of leaf surfaces. Symptoms first appear as light green spots and change to red and brown as the disease progresses. Prevent fungal leaf spot infection by increasing air circulation to prevent free moisture on leaf surfaces and apply fungicides to control severe infections.

Bacterial leaf spot is a disease of Viburnum, caused by the bacterium Pseudomonas syringae. The disease initially causes sunken water-soaked leaf spots. As the disease progresses, the spots enlarge and turn brown, leaf growth becomes distorted and shoot dieback can occur. The bacterium overwinters in infected twigs and buds, so remove them to prevent perennial infection. Prune overgrown branches to increase airflow and avoid overhead irrigation to prevent infection. Copper-based bactericides help reduce the spread of new infections.

  • Viburnum is susceptible to several fungal leaf spot diseases including Cercospora, Phoma, Phyllosticta and Plasmopara viburni (downy mildew).
  • Prevent fungal leaf spot infection by increasing air circulation to prevent free moisture on leaf surfaces and apply fungicides to control severe infections.

Snowball Bush Viburnum Care

The snowball bush viburnum is relatively easy to care for. You can plant it in the spring or fall make sure to dig a shallow and broad hole that is as deep as the root ball but two to three times wider. Fill the hole with the removed soil, with the root crown remaining about two inches above the soil level. Water the newly planted bush well and place mulch around it about four inches deep.

When choosing a spot for your plant, keep in mind that it will grow fairly large. Pick a spot that will provide lots of sun and allow for the mature size of the bush. Since this deciduous bush can compete with native plants for soil nutrients and habitat space, many states have declared this plant an invasive, ecological threat. Because of this, solitary placement could assist in ensuring the viburnum does not interfere with the health of other native plants. Once established, the shrub will be low maintenance. It should be fertilized only once per year and you may want to do some pruning.

Light

The best location for the shrub will be one in full sun, especially in cooler Northern states. The snowball bush likes at least six hours of sunlight per day in order to produce the biggest masses of flowers. A location in partial shade may be advisable for gardeners in a location that gets consistently warmer weather.

The snowball bush prefers well-drained, loamy soil but it isn't too particular and will grow well in many different soil types. It also tolerates a wide range of soil pH, but slightly acid is best.

Water

Water your snowball bush enough to keep its soil evenly moist, as it does not like dry ground. A suggested schedule is weekly, but you should plan to water it more often if experiencing extreme heat. Additionally, you can conserve soil moisture by applying a three-inch layer of landscape mulch around your shrub, which will have the bonus effect of suppressing weeds.

Temperature and Humidity

The snowball bush can tolerate fairly harsh winters and is drought-hardy once established. Additionally, it doesn't have any special humidity needs.

Fertilizer

Fertilize your snowball bush plant in the spring with a slow-release fertilizer, or work compost into the earth around the plant at any time. Be careful not to go overboard—fertilizing too much can inhibit the plant's blossoms.


Blights and Rots

Bacterial blight, caused by the Pseudomonas syringae bacteria, causes various degrees of damage, depending on the specific strain of fungus attacking the viburnum. General symptoms include brown or black spots on foliage, stem dieback, black lesions and cankers. Bacterial blight persists in overly wet conditions and unfortunately, there is no chemical cure. To control the fungus, remove infected limbs from the plant. Healthy shrubs can typically survive attacks of blights if the infection is confined to the leaves. Phytophthora rot attacks the crowns and roots of the viburnum causing discolored and dull foliage. This fungal disease is prevalent in wet conditions and creates dark areas on the bark, which ooze sap. Control of phytophtohora requires proper site preparation by ensuring the plant is grown in a well-drained location. Furthermore, push the soil near the base of the plant away to expose the main roots and help the crown tissue to dry quicker.


Problems of Viburnum

Leaves Curled, Discolored due to Aphids
Aphids, also called "plant lice," attack tender branches and flower clusters. The pests are spindly-legged, pear-shaped insects little bigger than the head of a pin. They suck sap from leaves and stems, causing the foliage to curl, pucker, and turn yellow, while reducing the plant's vigor. Ants, attracted by the aphids' honeydew secretions, wander over the plants and protect the aphids from natural predators. Check leaf undersides for small groups of aphids. For light infestations, spray leaf undersides vigorously with water three times, once every other day, in the early morning. Eliminate nearby ant nests if possible. Use insecticidal soap every 2 to 3 days for heavier infestations. As a last resort, use pyrethrum spray.
For more information see file on Controlling Aphids.

Foliage And Flowers Skeletonized means Asiatic Garden Beetles
Asiatic garden beetles skeletonize new leaves, flowers, roots and the bases of young stems. They are most active at night. The larvae (grubs), which are grayish, 3/4 inch long, and bent in a C-shape like Japanese beetle grubs, live underground and eat the roots. The adults are velvety chestnut-brown, nearly 1/2 inch long, resembling Japanese beetles. They lay their eggs in the soil at the base of the plants. Immediate control steps include handpicking and applying beneficial nematodes to the soil. For long-term control, apply milky spore disease (Bacillus popillae) powder to the soil. In the spring, carefully cultivate the soil around the shrubs to expose insect eggs, larvae and pupae to the weather and to birds. Avoid damaging the roots. For more information see the file on Controlling Asiatic Garden Beetle.

Holes In Twigs, Exuding Sawdust indicates Dogwood Twig Borers
Borers enter stem tips and bore out some of the twigs soon after blooming time. As they grow, these larvae bore into the main stems, pushing out fine sawdust as they go. The borers' activity leaves ugly scars and sometimes kills large branches. Dogwood twig borer grubs are dull yellow, 3/4 inch long. They winter over in the twigs of the viburnum. Adult beetles appear in the spring. In June, crush any eggs that you can find. An effective but tedious remedy is to shove a wire into each borer hole to crush or remove the borer. Try injecting nicotine paste into borer holes. The most complete control is to prune and burn affected stems if you can avoid deforming the shrub.
For more information see file on Controlling Borers.

Plant Stunted, Leaves Yellowed Root Lesions because of Nematodes
Plants infested with nematodes look sickly, wilted, and stunted. They develop yellowed or bronzed foliage, decline slowly and eventually die. Their root systems are poorly developed, even partially decayed. Southern root knot nematodes attack Viburnums. These are slender, unsegmented roundworms that live in the soil. They're less than 1/-inch long, invisible to the unaided eye. They have piercing-sucking mouthparts. Add lots of compost (especially decomposed leaves) to the soil around the Viburnum plants to encourage beneficial fungi that attack nematodes. Liquid fish emulsion, poured into the soil as a drench, is toxic or repellent to nematodes. Try inter-planting French marigolds among the Viburnum plants their root exudations repel or kill nematodes.

Leaves And Branches Encrusted With Small Bumps caused by Scale Insects
The first sign of a scale attack is often discoloration of upper leaf surfaces, followed by leaf drop, reduced growth, and stunted shrubs. Aptly named, scale insects are covered by hard, rounded waxy shells, which are colored white, yellow, or brown to black. They are about 1/10 to 2/5 inch in diameter. Heavy scale infestations may kill viburnums. Some species of scale insects excrete honeydew, which coats foliage and encourages ants and the growth of sooty mold, a gray to black coating on the leaves and stems. Early on, you can scrape scale off plant surfaces with your fingernail or a cotton swab dipped in rubbing alcohol. Spray more heavily infested plants with a mixture of alcohol and insecticidal soap every three days for two weeks. Mix 1 cup of rubbing alcohol and 1 tablespoon of insecticidal soap concentrate in 1 quart water. If your insecticidal soap is already mixed with water, add 1 tablespoon of alcohol to a pint of the diluted soap spray.
For more information see file on Controlling Scale

Leaves Have Silvery Pallor due to Thrips
Thrips damage results from these insects' habit of rasping at plant cells and sucking sap from the injury. Viburnum leaf surfaces are flecked and whitened leaf tips whither, curl and die. Leaf undersides are spotted with tiny black specks of excrement. Adult thrips are tiny, slender insects, 1/25 inch long. They are variously colored--pale yellowish, black or brown. They have 4 long, narrow wings fringed with long hairs and very short legs. Their larvae are usually wingless. Since thrips burrow deeply between flower petals, early identification and control are necessary. Set out yellow sticky traps about 4 weeks after last frost as early warning devices. As soon as you spot thrips on the trap, apply a spray of insecticidal soap every 3 days for 2 weeks. Commercially available predatory mites, lacewings, ladybugs and beneficial nematodes are effective backups to the soap spray. Thrips prefer a dry environment, so make sure plants are adequately misted or watered. For more information see the file on Controlling Thrips

Sunken Spots on Leaves means Anthracnose
This fungus disease forms distinct lesions on leaves, which appear as moist, sunken spots with fruiting bodies in the center. The spots may run together, resembling a blotch. The dead areas follow the veins or stop at larger veins. Sometimes terminal shoots die down to several inches below the buds. Gather and destroy diseased leaves when they fall and prune away diseased branches. Maintain plant vigor by feeding and watering well, especially during droughts. Spray with a copper fungicide such as Bordeaux mixture.
For more information see file on Controlling Fungal Disease

Buds and Flowers Spotted, Leaves Blotched indicates Blight
When infected by this fungus disease, flowers become spotted, spots enlarge into blotches, and the flowers deteriorate. Leaves develop grayish brown decayed patches. The fungus attacks dense flower clusters during wet weather. Spray plants with copper fungicide when symptoms first appear and then every 10 days in wet seasons. Avoid overhead watering. Prune to increase air circulation around plants, taking care to sterilize pruning tools by dipping them in household bleach to prevent the disease from spreading.
For more information see file on Controlling Fungal Disease

Tumor-like Swellings on Stems because of Crown Galls
A bacterium infects viburnum shrubs through wounds. It stimulates cells to form tumor-like swellings (galls) with irregular rough surfaces along the stems. Serious infection causes branches to die back. Prune out and discard all branches bearing galls.

Dead Blotches on Leaves caused by Leaf Spot
Various leaf spot fungi cause yellow, brown or black dead blotches on the leaves that frequently run together. Heavily infected leaves turn yellow or brown and fall prematurely. Cool, moist weather favors these diseases, especially when new leaves are developing. Shake out all fallen and diseased leaves from the center of the viburnum shrubs and destroy them. Remove all dead branches in the center of specimen plants or hedges to allow better aeration. Mulching helps prevent the disease from splashing up from the ground and infecting plants. Spray at weekly to 10-day intervals with sulfur or Bordeaux mixture or other copper fungicide, particularly in rainy weather. Cut down and discard seriously infected shrubs together with the soil ball.
(Note: Sulfur-based fungicides may harm some viburnum varieties. Test the sensitivity of your particular Viburnum by treating one branch and watching it for 3 days to see if any discoloration occurs. If the branch and leaves seem to be unaffected after that time, you should be able to use sulfur on the plant.)
For more information see file on Controlling Fungal Disease

Leaves Covered With White Powder due to Powdery Mildew
Powdery mildew, caused by a fungus, develops mostly on the upper surfaces of viburnum leaves and appears as whitish blotches. In late summer, bushes in shady spots may be badly infected. If the disease is serious, spray thoroughly with wettable sulfur once or twice at weekly intervals, starting as soon as the whitish coating of the fungus is visible. Collect and discard all plant refuse in the fall.
For more information see file on Controlling Fungal Disease

Rust Colored Spots on Leaves means Rust
Rust infections usually appear as numerous rust-colored, orange, yellow or white, powdery, raised localized spots. Infected leaves wilt and wither and the plants may be stunted. Rusts are caused by various fungi that attack leaves and stems and sometimes flowers. Remove infected leaves as soon as possible. Remove and destroy diseased plants and all debris before growth starts in the spring.
For more information see file on Controlling Fungal Disease

Foliage Burned indicates Dog Urine
Urination by dogs may discolor foliage and even kill branches. Spraying foliage with an anti transpirant gives some protection. Screen the plants or spray with an aerosol pet repellant. For more information see the file on Dealing With Dogs and Cats

Bark of Trunk and Roots Gnawed because of Rodent Injury
Small rodents gnaw bark off trunks, causing injury that allows disease organisms to invade. Rake mulch away from tree bases during the winter keep the area clear of weeds and grass and wrap the trunk base with a guard of 1/4-inch hardware cloth.
For more information see files on Dealing With Mice and Dealing With Rabbits and Dealing With Voles

Do you have a gardening question? Ask Nancy


Hello, All 3 of my Viburnum Cardinal Candy (Viburnum dilatatum 'Henneke') have many of the leaves turning brown from the outside edge going inward, curling and becoming crispy. Planted on 4-20-2018. Any help would be appreciated. Thanks, John

The type of drying that the photos show appears to be from desiccation/drying. That can be a result of water-deficit/drought-stress or fertilizer burn. High Nitrogen, high salt index chemical fertilizers can desiccate roots and therefore restrict uptake of water. The extremes of the leaf tips and leaf margins dry up first. If the condition is severe the drying can continue into wider scale leaf burn and die-back.

This link is for an article on viburnum leaf browning, for your general information. But I don't believe your plants are suffering from any of the fungal disorders indicated.


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