Viburnum leaves turning brown

Brown Viburnum Leaves: Why Leaves Turn Brown On Viburnum

Many gardeners decide to plant viburnumbecause it is usually pest free. However, sometimes the plant does have disease problems that cause brown viburnum leaves. Why do viburnum leaves turn brown? Read on for information about the different reasons you might see brown leaves on viburnum plants.

Viburnum Leaves Turning Brown

So why do viburnum leaves turn brown? In most cases, fungus is to blame. Below are the most common situations for browning in these plants:

Fungal spot or Anthracnose

Take a close look at your browning viburnum leaves. If they have irregular brown spots that are sunken and dry, they may have a fungal spot disease. The spots begin small but merge together and may appear red or gray.

Among the most common causes for viburnum leaves turning brown or black are leaf spot diseases. Don’t panic. Leaf spot fungal diseases, as well as the fungal disease anthracnose, usually do not do lasting harm to your plants.

Keeping leaves relatively dry is the key to preventing leaf spot diseases where leaves turn brown on viburnum. Do not use overhead irrigation and leave sufficient space between your plants for air to pass through. Rake up and burn the brown viburnum leaves that have fallen.

If the brown leaves on viburnum are caused by leaf spot disease or anthracnose, you can treat the plants with fungicides available in commerce. For example, treat anthracnose by spraying the leaves with a copper fungicide.

Powdery or Downy Mildew

Mildew diseases can also be a reason leaves turn brown on viburnum species. Both powdery mildew and downy mildew can result in brown viburnum leaves as the foliage dies. You’ll see mildew diseases more often during times of humidity. Plants sited in shade suffer most from them.

The tops of viburnum leaves infected by powdery mildew are covered with a powdery fungal growth. This usually happens in summer. Downy mildew causes light green spots mostly on the lower leaves. Leaves that die from these infections turn brown.

If your leaves turn brown on viburnum because of mildew diseases, take steps to reduce water on them by using the same tips as for leaf spot diseases. You can also control mildew by spraying fungicides containing horticultural oil.

Rust

If the spots on your viburnum leaves are more rust-colored than brown, the plants may have a rust infection. This is also caused by various fungi. Viburnum leaves infected by rust will wither and die. This is a contagious disease, so you’ll want to destroy diseased plants in the spring before new growth starts.

Other reasons for leaf browning

Dog urine also causes viburnum leaves to brown. If you have a male dog that runs in your garden, this may explain the brown viburnum leaves.

We had several complaints of viburnum problems at the University of Illinois Plant Clinic toward the end of the summer. Usually, the descriptions included branch decline, plants that looked like they were dying, and early defoliation. We rarely hear of problems on viburnum, so it was odd to receive several such complaints on this host. This article describes some of the problems that may appear on viburnum, with comments on how you might use this information to work through a diagnosis. Solving plant problems requires information about the symptom development, the plant site, and the environment … really!

It helps to know what diseases are possible on a given host. Viburnums sometimes have problems with foliar diseases, including bacterial leaf spot, downy mildew, and powdery mildew. Bacterial leaf spot is a disease present in cool, wet weather. It causes angular leaf spots that appear water-soaked. The reported problem appeared in hot, dry weather of late summer. In addition, leaf spots were not apparent. The leaves were dying but not spotted. Downy mildew is another disease that is favored by cool, moist conditions. It causes angular leaf spots much like bacterial leaf spot; but lesions start out yellow, become brown, and may coalesce to form large brown blotches. Downy mildew also forms a fine, downy growth on the underside of these lesions. Again, no leaf spots were reported on the injured plants. Powdery mildew causes a white, dry, powdery growth on the leaves and certainly could be a problem in late summer. Severe cases can cause some leaf deformation and even some leaf drop, but stems should remain alive. Growers reported that stems were dying. Powdery mildew is also a disease that most growers recognize. None of these foliar diseases seemed likely, based on the problem description. Often, however, the description of the problem does not always match the actual symptoms. We received one suspect viburnum sample. In fact, it did not contain any leaf spots. Leaves were sectioned and found to be free of bacteria. Lab incubations of leaves did not yield any fungal pathogens.

Despite the fact that I am a pathologist, I am quick to point out that not all plant problems are caused by disease. It seemed logical to suspect a water deficit or heat problems. It also seemed logical to question root injury, insect borer activity in the stems, and time of planting (to rule out transplant shock). Further questioning revealed that this was an established bed of viburnums and that most of the plants in the front row were affected, while the back row appeared better.

Viburnums are susceptible to Verticillium wilt. The wood submitted was cultured in our lab when it arrived. There was no vascular discoloration. Eventually, cultures proved negative for this vascular pathogen. We could rule out Verticillium wilt.

Lower stems were cankered. These cankers were not extremely obvious, but they were present on the sample. Incubated tissue yielded a form of the Botryosphaeria fungus. Yes, the diagnosis was Botryosphaeria canker, but that is not the entire story. The back row of plants was not yet affected. As is often the case, the fungal pathogen was not able to cause a problem on its own. Botryosphaeria is a stress pathogen. When I looked in the literature, I found that the most common stress factor associated with viburnums and Botryosphaeria was drought. Discussion with the grower revealed that this area had been very dry. Management of the problem was not a matter of spraying a fungicide. In this case, we recommended removal of dead wood, supplemental watering until the ground freezes, and a light application of fertilizer. The grower realizes that he needs to monitor water deficits more closely in the future. Plant problem management depends on an accurate assessment of the problem (site stress and disease in this case) followed by alteration of factors that can be corrected.

(Answer)

Thank you for contacting Toronto Master Gardeners.

It would appear that you have some type of leaf spot disease on your Viburnum. The exact type is difficult to determine.

It is not possible to identify the exact disease from a photo. The following links will take you to websites which discusses leaf spot diseases. By closely examining your shrub and comparing the symptoms to the photos on the site you may be able to narrow down the possibilities. The site also discusses management strategies.

It is imprtant to note that some leaf spot diseases are caused by fungi; some by bacteria. With any disease of this type, the best practice is to remove the affected leaves and destroy the leaf debris, and this includes leaves that fall at the end of the season because often spores or bacteria will overwinter in fallen leaves, or in twigs. Do not put the leaves in your compost but put them either in the City of Toronto’s leaf pick up or the garbage. Your compost will not get hot enough to destroy fungi and spores.

We have a several helpful Q&A posted on our website that might help. The link is noted below:

What is eating the leaves of my viburnum?

If you’re noticing lots of holes in the leaves of your viburnums from late spring through summer, chances are good that you have viburnum leaf beetle (VLB). Native to Europe, VLB was accidentally introduced to North America sometime in the last century. Since then, it has become a significant landscape pest and has discouraged the planting of susceptible viburnum species.

VLB larva hatch in mid to late spring and immediately start feeding on their host plants. Larva are initially greenish-yellow, turning yellow-brown with black spots as they develop, reaching a total length of about 10 mm. Larva usually feed on the undersides of leaves, making them difficult to spot, especially when they are small. Groups of larva will often feed on the same leaf, exacerbating damage further. The tell-tale mark of VLB feeding is “skeletonized” leaves, or in other words, leaves that have been eaten between the major leaf veins, leaving the leaf mid-rib intact.


Viburnum leaf beatle larvae. Milan Zubrik, Forest Research Institute – Slovakia, Bugwood.org.

In late June through early July, VLB larva crawl down the trunk of the shrub to the ground to pupate in the soil. In a very short amount of time adult beetles emerge and begin feeding on viburnum foliage once again, creating distinctive irregular oblong holes in the leaves. In fact, it takes as little as 8-10 weeks to go from hatching to adult. When they aren’t damaging plants, VLB adults are mating and laying eggs on the new growth of viburnum shrubs. Females chew small holes in twigs and lay around eight eggs inside each, sealing up the cavities with a cap made of excrement and chewed bark. Rows of 1-2mm brownish-black bumps on the undersides of new growth are the evidence of VLB egg laying. Adult females can lay hundreds of eggs before the first killing frost.

The most important management strategy is to remove and destroy egg-infested twigs, which are easiest to locate once the plant has dropped its leaves between October and April. Encouraging beneficial insects is also key. Lady beetles, lacewings, spined soldier bugs, and assassin bugs are all known to prey upon VLB and provide a good measure of control. Boost their populations by avoiding the use of broad-spectrum insecticides and maintaining or increasing plant diversity in the yard and garden. Chemical control options should be viewed as a last resort. Some insecticides are registered for use against VLB and are generally most effective if applied when larva are active. Spinosad and insecticidal soap are slightly friendlier options in terms of protecting beneficial insects, but they must come in direct contact with larva to be effective.

Know that some viburnums are more susceptible to VLB than others. Arrowwood (Viburnum dentatum), European cranberrybush (V. opulus), American cranberrybush (V. opulus var. americana), and downy arrowwood (V. rafinesquianum) are especially attractive to the pest and frequently suffer considerable damage. Avoid VLB problems from the start by planting resistant species such as Koreanspice viburnum (Viburnum carlesii), siebold viburnum (V. sieboldii), witherod viburnum (V. cassinoides), and blackhaw viburnum (V. prunifolium).

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Black-haw viburnum

Size & form

12 to 15 feet high and 8 to 12 feet wide
A large, suckering shrub or single-trunked tree

Tree & Plant Care

Adaptable to most sites, wet, dry, sun or shade.
Can form thickets
Flowers on old wood, prune after flowering
Tolerant of black walnut toxicity and aerial salt spray

Disease, pests, and problems

No serious problems

Native geographic location and habitat

C-Value: 5
Most common in woods and forest edges. Tolerant of roadside edges to stream banks.

Attracts birds & butterflies

Provides food and shelter to many bird species

Bark color and texture

Mature bark is brownish and broken into a blocky pattern
Young stems are slender and straight with a pinkish bloom on reddish stems.
Leaf scars are V-shaped and slightly raised.

Leaf or needle arrangement, size, shape, and texture

Opposite leaves up to 3 to 4 inches long, narrow to oval with serrated edges. Leaf tip pointed.
Leaf surface smooth and medium green with a lighter underside, Leaves turn reddish-purple in fall.
Often confused with Nannyberry (Viburnum lentago). Petioles are reddish but not winged like nannyberry.
Two types of terminal buds during winter months.

Flower arrangement, shape, and size

Small, creamy white flowers in flat-topped to slightly domed clusters, slightly fragrant.
Flower buds in winter are larger, bulbous, pinkish at ends of stems.

Fruit, cone, nut, and seed descriptions Black-haw fruit photo: John Hagstrom

Berry-like fruits (drupes) turn a dark blue or black in fall

Cultivars and their differences

“This plant is a cultivar of a species that is native to the Chicago Region according to Swink and Wilhelm’s Plants of the Chicago Region, with updates made according to current research. Cultivars are plants produced in cultivation by selective breeding or via vegetative propagation from wild plants identified to have desirable traits.”

Guardian™ black-haw viburnum (Viburnum prunifolium ‘Guazam’): Upright habit grows 10 to 12 feet high and 6 to 8 feet wide, dark green foliage turns crimson-red in late fall

Forest Rouge™ black-haw viburnum (Viburnum prunifolium ‘McKrouge’): Oval to upright small tree or large shrub reaching 8 to 10 feet high; outstanding maroon fall color

Summer Magic black-haw viburnum (Viburnum prunifolium ‘Summer Magic’): Upright habit reaching 8 to 10 feet high and 6 to 8 feet wide; new growth emerges reddish-pink, leathery leaves turn yellow to red in fall

Viburnum Diseases & Insect Pests

In general, most viburnums are relatively pest-free. Occasionally disease or insect pest problems do occur, and usually it is during those times that the plants are under stress or growing in less than ideal conditions.

Fungal Leaf Spots

A variety of leaf spots are caused by the fungi Cercospora spp., Phoma spp., and Phyllosticta spp. These fungal leaf spots on viburnum typically are angular to irregular-shaped, and the leaf tissue in the spots is sunken and dry. Spots may begin small, but enlarge or merge , and may be reddish to grayish brown. Fungal leaf spots typically occur during warm, moist summer months, and initially will occur on older foliage. The disease anthracnose (caused by Colletotrichum spp.), appears as black, sunken lesions. Leaf spots and anthracnose are fairly common on viburnum foliage, but these foliar diseases are not usually serious.

Prevention & Control: Many foliar problems can be prevented by keeping leaves as dry as possible. Avoid overhead irrigation and improve air circulation with adequate plant spacing and selective branch pruning. Prune overhanging trees around diseased shrubs to reduce humidity levels and speed the drying of foliage. Hand remove spotted leaves on lightly diseased plants. Rake up and destroy infected fallen leaves. The removal of this leaf material will minimize the chances of the disease reoccurring the next season.

If chemical control is needed, most fungal leaf spots and anthracnose can be controlled with sprays of fungicides containing chlorothalonil, thiophanate-methyl, myclobutanil, or mancozeb. Apply when symptoms first appear and repeat every 10 to 14 days as needed.

Algal Leaf Spot

Algal leaf spot, caused by Cephaleuros virescens, may occur especially during cool, moist conditions. Leaf spots start as small, pale green circular spots, and eventually become light brown or reddish brown with age. Often the spots appear raised and velvety with feathered edges. When the spots become reddish-brown, they are producing their reproductive structures called sporangia. These sporangia are spread to adjacent foliage by wind and splashing rain. This pathogen will overwinter in leaf spots.

Prevention & Control: Algal leaf spots are common on several ornamental shrubs and trees, including camellias, magnolias, azaleas, aucubas, gardenias, and rhododendrons. Monitor the plants for disease problems, practice good sanitation as stated with fungal leaf spot control, and treat any other landscape plants in the area that have algal leaf spot.

Algal leaf spot can be controlled with sprays of copper fungicides (see Table 1 for specific products). Apply when symptoms first appear and repeat every 10 to 14 days as needed.

Powdery Mildew

Viburnum species may become diseased with powdery mildew, caused by the fungus, Erysiphe sparsa (formerly Microsphaera sparsa). The occurrence and spread of this disease is favored by a combination of warm days, cool nights, and humid conditions, but is inhibited by rain. Powdery mildew is worse on plants in the shade.

Powdery mildew of viburnum primarily affects young leaves and shoots. Affected plant tissues develop a powdery white to light gray growth of fungal mycelia. The fungus is mostly found on the upper leaf surface, but also may be found on the lower leaf surface. The disease typically appears in the summer and reaches its peak in late summer. Developing leaves may be deformed by severe infections.

Prevention & Control: Since high relative humidity is an important factor favoring disease development, certain cultural practices can help prevent the disease or decrease its severity. Sanitation and measures discussed for fungal leaf spot control will aid in powdery mildew control. Additionally, some cultivars, such as Viburnum burkwoodii ‘Mohawk’ and V. carlecephalum ‘Cayuga’ exhibit some resistance to powdery mildew.

Powdery mildew can be controlled with sprays of fungicides containing myclobutanil, propiconazole, thiophanate-methyl, or horticultural oil (see Table 1 for specific products). To prevent foliar injury, apply horticultural oils for powdery mildew control only if temperatures are below 85 °F. Although sulfur is sometimes used for powdery mildew control, it is not recommended for sulfur-sensitive plants, such as viburnums.

Downy Mildew

Downy mildew on viburnum is caused by the fungus, Plasmopara viburni. This foliar disease occurs and spreads rapidly during cool to warm weather conditions coupled with periods of leaf wetness. Initially, this disease appears as light green spots on the upper leaf surfaces. The spots enlarge to form angular patches between the leaf veins. On the lower leaf surfaces downy grayish white fungal growth appears.

Downy mildew disease is different from powdery mildew in that the fungal growth is observed on the lower rather than on the upper leaf surface. The infected areas redden and then turn brown as the leaf tissue dies. Infections of the foliage in the spring can result from splashing spores produced by the diseased foliage remaining on the ground from the previous year.

Prevention & Control: As with other foliar diseases, downy mildew can be prevented by keeping the foliage as dry as possible. When planting viburnum or other nearby plants, allow for adequate plant spacing. Prune back adjacent shrubs or overhanging tree limbs. These steps will improve air circulation around the plants and aid in the drying of foliage. Rake up and destroy infected fallen leaves.

If fungicides are necessary, sprays should adequately cover both the upper and lower leaf surfaces. Fungicides labeled to control downy mildew include mancozeb, chlorothalonil, or copper fungicides (see Table 1 for specific products).

Botryosphaeria Dieback & Canker

The fungal disease called Botryosphaeria dieback and canker, caused by Botryosphaeria spp., is most likely to occur on plants suffering from drought stress, bark injuries, pruning wounds, or other environmental stresses. Healthy plants are much more resistant to infection by Botryosphaeria spp., as they will wall off the fungus and prevent its spread through the branch.

Upon entry via a wound, the fungus kills cambium and sapwood tissue, causing sunken dead areas called cankers. The cankers are small initially, but enlarge or coalesce (merge) into large areas that girdle the branch or trunk. Water movement is stopped beyond that point and results in a rapid wilting or browning of foliage. Branches with cankers may fail to leaf out in the spring.

Prevention & Control: Water shrubs weekly during the growing season if insufficient rainfall occurs (see HGIC 1056, Watering Shrubs & Trees). Mulching shrubs helps to avoid mechanical injury to trunk and limbs by weed trimmers and lawn mowers. Mulch shrubs with a 2- to 4-inch layer of bark, pine needles or ground leaves, and avoid piling the mulch against the trunk.

Prune any branches with cankers back to green healthy wood. If entire branches must be pruned, cut the limb just outside the branch collar and not flush with the trunk. Disinfest pruners between every cut with a 70% alcohol or 10% bleach solution. Dispose of all prunings, as this plant material is a potential source of disease for viburnums, as well as other woody shrubs. No fungicides are recommended for the control of fungal cankers, but pruning wounds may be sprayed for protection with a benzimidazole fungicide, such as thiophanate methyl (see Table 1 for specific products).

Armillaria Root Rot

Armillaria root rot (Armillaria spp.).
Andrej Kunca, National Forest Centre – Slovakia, Bugwood.org

Armillaria root rot is also known as shoestring root rot, mushroom root rot, and oak root rot. It is caused by the fungus Armillaria mellea, which is common in landscape and garden settings. This fungus can rot the roots of many different kinds of plants. Most often this disease is found on trees and shrubs, such as oak, pine, rhododendron, and dogwood, but hundreds of plant species, including viburnums, are susceptible. Typically, the symptoms of this root rot occur over the whole plant. Above-ground parts of the shrub generally appear stunted and yellowed and leaves may drop. The unhealthy foliage may become more sparse over a period of several years. However, there may be no evidence of any problems, and suddenly the shrub will die. The cause of the unhealthiness or death may be difficult to determine, as similar symptoms may be caused by environmental factors, such as weather stress or a general lack of plant care.

Armillaria root rot can be distinguished from other root rots, from droughts or excess moisture injury, by examining the crown (lower trunk) and upper roots of the plant. If Armillaria is responsible for the plants decline, white felt-like fungal growth can be seen under the bark if the bark is carefully peeled back. If sufficient bark is removed, the leading edge of the fungal growth will be found, and this white growth has a characteristic fan-shape. The Armillaria root rot fungus also forms black, string-like fungal strands about 1/16-inch in diameter or less. These strands may often be seen between the bark and the wood, or on the surface of the roots, or in the nearby soil. These string-like fungal strands are called shoestrings, and look very similar to roots.

Prevention & Control: Provide good growing conditions for the viburnum, especially additional water during droughts, good soil drainage, and proper fertilization.

An infected shrub whose entire root system or trunk is diseased cannot be saved. When a shrub dies from Armillaria root rot, the large roots in the vicinity of the trunk as well as the trunk itself should be removed and destroyed. Soil in the immediate vicinity should also be removed. Avoid replanting the same species as the one removed.

Aphids

Snowball aphids (Neoceruraphis viburnicola) most often occur on European cranberry bush and snowball viburnums. They can cause twisting and curling of the young growth. These aphids are gray to dark green and feed in clusters at the tips of the branches, causing leaf curl. They feed by piercing plant tissue and sucking plant sap.

Prevention & Control: They usually cause little or no appreciable damage. Viburnums can be sprayed with insecticidal soap or horticultural oil to control aphids. Soaps and oils must be sprayed onto the aphids to be effective. Spray the foliage thoroughly, including the upper and lower leaf surfaces. Repeat spray three times at 5- to 7-day intervals. Only apply horticultural oils or insecticidal soaps if temperatures are below 85 °F.

If higher toxicity insecticides are deemed necessary, sprays containing acephate, bifenthrin, cyfluthrin, lambda cyhalothrin, malathion, neem oil, permethrin, or pyrethrin will control aphids. Soil drenches or granular applications of imidacloprid or dinotefuran will control aphids and last longer within the plant to prevent future infestations (see Table 1 for specific products).

Flower Thrips

Flower thrips (Frankliniella spp.).
Jack T. Reed, Mississippi State University, Bugwood.org

Flower thrips (Frankliniella tritici) and various other thrips species are pests of viburnums. Thrips are slender, dark-colored insects, with fringed wings. Adults are less than 1/16-inch in length. To see these fast-moving pests, you need a magnifying lens. Thrips are typically found on leaves and between flower petals. Both adults and nymphs (immature insect stage that resemble the adult, but are smaller) feed by scraping surface cells to suck plant sap. Thrips feed on expanding leaves, which creates purplish red spots on the undersurfaces and causes foliage to severely curl or roll, then drop prematurely.

When they feed on flower buds, the flower may die without opening. With a light infestation, their feeding causes leaves to have silvery speckles or streaks. With severe infestations, leaves and flowers are stunted and distorted and may turn brown and die. As a result of their small size, thrips are difficult to detect before damage is obvious. To sample for thrips on viburnum foliage, hold a sheet of stiff white paper under injured leaves, and then shake or tap the branch. Gently tip the paper to remove any bits of trash and then examine the paper in bright sunlight. Any thrips present will move around on the paper.

Prevention & Control: Several naturally occurring enemies feed on thrips. To avoid killing these beneficial insects which reduce thrips populations, insecticides should be avoided as much as possible. Grass and weeds in the area should be kept mowed or removed when possible.

If it becomes essential to spray an insecticide, the following are available in homeowner size packaging: acephate, bifenthrin, cyfluthrin, lambda cyhalothrin, permethrin, or spinosad. Spray when thrips are present and again in 7 to 10 days. Insecticidal soaps will help control thrips, but thorough coverage is necessary. The soap spray must contact the pest to be effective, and may require three sprays at 5- to 7-day intervals. Soil drenches or granular applications of dinotefuran or imidacloprid will give some thrips suppression. See Table 1 for specific products.

Spider Mites

The southern red mite (Oligonychus illicis) is a dark reddish or brown-colored mite that is a common pest in the eastern US. Azaleas, camellias, and hollies are the primary hosts for this mite, but it has been found on many other species including viburnums. The southern red mite is active in the cool weather of spring and fall, and overwinters as eggs.

Mites have needle-like piercing-sucking mouthparts. Damage to the foliage begins on the lower leaf surface where feeding begins, but as populations increase, the upper leaf surface is fed upon as well. Over time the leaf tissue collapses, the foliage turns grayish-brown, and the damaged foliage drops.

Prevention & Control: Spider mites can be removed with strong sprays of water, if applied on a regular basis. Insecticidal soap or horticultural oil are the least toxic alternatives to beneficial insects, people and the environment and can provide control when applied before population numbers get too high. Both the lower and upper leaf surfaces must be sprayed for good control. Two or three applications may be required at 7- to 14-day intervals. To determine if additional spray treatments are needed, shake or tap branches over a piece of white paper. Then look for reddish-brown specks that move around.

The following pesticide is labeled for use by homeowners against spider mites: tau-fluvalenate (see Table 1 for specific products). These miticides should be applied when mites are present and again in 7 to 10 days.

Scale

Oystershell scale (Lepidosaphes ulmi).
Whitney Crabshawm Colorado State University, Bugwood.org

Armored scales, such as the oystershell scale (Lepidosaphes ulmi), can infest viburnum and cause branch dieback. If the infestation is severe enough, they may kill the shrub.

The oystershell scale can overwinter as full grown females that are attached to the bark, or as eggs that are beneath the adult scale covering. The adult female is 1/8-inch long, brown or gray, and generally the shape of an oyster shell.

Crawler (immature stage) activity often coincides with the flush of new plant growth in the spring. These crawlers are pale, smaller than a pinhead and are the only mobile stage of the scale life cycle. Within a few hours, the crawlers will settle in a suitable spot to begin feeding and excreting a waxy covering for protection.

Prevention & Control: Light infestations of scale can be scraped off by hand. Prune out and dispose of any heavily infested branches. A 2% horticultural oil can be sprayed in the early spring before new growth begins to kill overwintering adults and eggs. Horticultural oil may be sprayed when temperatures are between 40 and 85 °F.

Monitor the crawler emergence in the spring with sticky cards, double-faced tape wrapped around a branch, or by putting an infested shoot or leaf into a baggie and watching for crawler movement. Spray with horticultural oil in the spring after the plants begin growing and the danger of cold weather has passed. Repeat this application after 10 days to better control the crawlers, adults, and eggs by smothering them.

Avoid using more toxic insecticides unless the plant is seriously damaged from the scale infestation. These insecticides will often kill the naturally occurring predators of scale. If insecticides are going to be used, spray when crawlers are observed, as this is the only stage in the life cycle that is controlled by contact insecticides. Insecticides labeled for homeowner use against scale crawlers include acephate, malathion, bifenthrin, cyhalothrin, and cyfluthrin (see Table 1 for specific products). Alternatively, a soil application of a product containing dinotefuran may be applied for scale control on viburnums.

Root Weevils

Root weevil adults, such as the black vine weevil (Otiorhynchus sulcatus), feed on foliage, and the injury shows up as ragged notches on the leaf edges. Although the foliar damage is not generally severe, it can be very unsightly. The adult weevil is a black, wingless weevil about ⅜-inch long. The adults are noctural feeders and move up onto the plant at sundown. On sunny days, they are found in the leaf litter beneath the viburnum canopy.

Root weevil larvae cause damage by chewing and girdling roots, and damage usually begins in spring to early summer and continues through the growing season. The larvae are white, legless grubs with a brown head and C-shaped appearance. They are found in the soil around the viburnum roots.

The grubs cause more significant damage than do the adults. Plant growth may become stunted, and the foliage may become pale green or yellow. Root and crown feeding by the grubs may kill the shrub.

Prevention & Control: For successful control, treatments should be directed at the adult weevils. Once foliar damage is observed, insecticidal sprays should be made at 2- to 3-week intervals, where three sprays are usually sufficient. Along with the foliar applications, also treat the surface of the soil or mulch immediately beneath the plants (as a spray, not a drench) because this is where the adults will hide during the day. Insecticides labeled for adult weevil control include bifenthrin, acephate, permethrin, and cyfluthrin. A soil drench around the base of the shrub with imidacloprid or dinotefuran can be used to control the larvae (see Table 1 for specific products).

Table 1. Insecticides and Fungicides for Viburnum Insect Pest and Disease Control.

Active Ingredient Brand Names and Products
Acephate Bonide Systemic Insect Control Concentrate
Bifenthrin Ortho Bug-B-Gon MAX Insect Killer for Lawns & Gardens Concentrate
Hi-Yield Bug Blaster II Bifen 2.4 Concentrate
Bifen I/T Concentrate
Ferti-lome Broad Spectrum Insecticide Concentrate
TalStar P Concentrate
UpStar Gold Insecticide Concentrate
Chlorothalonil Hi-Yield Vegetable, Flower, Fruit & Ornamental Fungicide Concentrate
Ferti-lome Broad Spectrum Landscape & Garden Insecticide
Ortho Max Garden Disease Control Concentrate
GardenTech Daconil Fungicide Concentrate
Bonide Fung-onil Concentrate
Southern Ag Liquid Ornamental & Vegetable Fungicide
Tiger Brand Daconil
Copper Camelot O Fungicide/Bactericide Concentrate
Bonide Liquid Copper Concentrate
Bonide Copper Fungicide Wettable Powder
Natural Guard Copper Soap Fungicide
Monterey Liqui-Cop Fungicide Concentrate
Southern Ag Liquid Copper Fungicide
Cyfluthrin Bayer BioAdvanced Vegetable & Garden Insect Spray Concentrate
Dinotefuran Gordon’s Zylam Liquid Systemic Insecticide
Gordon’s Zylam 20SG Systemic Turf Insecticide
Valent Brand Safari 2G Insecticide
Valent Brand Safari 20SG Insecticide
Ortho Tree & Shrub Insect Control Ready to Use Granules
Horticultural oil Ferti-lome Horticulture Spray Concentrate
Southern Ag ParaFine Horticulture Oil Concentrate
Bonide All Seasons Spray Oil Concentrate
Monterey Horticultural Oil Concentrate
Summit Year Round Spray Oil Concentrate
Imidacloprid Bayer BioAdvanced Garden 12 month Tree & Shrub Insect Control Conc. (drench)
Bonide Annual Tree & Shrub Insect Control w/ Systemaxx (drench)
Ferti-lome Tree & Shrub Systemic Insect Drench
Hi-Yield Systemic Insect Spray (drench)
Monterey Once A Year Insect Control II (drench)
Insecticidal soap Bonide Insecticidal Soap Concentrate
Espoma Earth-tone Insecticidal Soap Concentrate
Natural Guard Insecticidal Soap Concentrate
Safer Brand Insect Killing Soap Concentrate
Garden Safe Insecticidal Soap Insect Killer Concentrate
Lambda cyhalothrin Spectracide Triazicide Insect Killer for Lawns & Landscapes Concentrate (also in RTS1)
Martin’s Cyonara Lawn & Garden Concentrate
Mancozeb Bonide Mancozeb Flowable with Zinc Concentrate
Southern Ag Dithane M-45
Malathion Spectracide Malathion Insect Spray Concentrate
Southern Ag Malathion 50% EC
Hi-Yield 55% Malathion Insect Spray Concentrate
Ortho Max Malathion Insect Spray Concentrate
Tiger Brand 50% Malathion Concentrate
Gordon’s Malathion 50% Spray Concentrate
Bonide Malathion Insect Control 50% Concentrate
Martin’s Malathion 50% Concentrate
Myclobutanil Spectracide Immunox Multi-Purpose Fungicide Concentrate (also in RTS1)
Ferti-lome F-Stop Lawn & Garden Fungicide Concentrate
Monterey Fungi-Max
Neem oil Southern Ag Triple Action Neem Oil Concentrate
Ferti-lome Rose, Flower & Vegetable Spray Concentrate
Monterey 70% Neem Oil Fungicide/Insecticide/ Miticide Conc.; & RTS1
Garden Safe Neem Oil Extract Concentrate; & RTS1
Garden Safe Fungicide 3 Concentrate
Safer Brand Neem oil Concentrate
Natural Guard Neem Concentrate
Permethrin Bonide Eight Insect Control Vegetable, Fruit & Flower Concentrate
Hi-Yield Kill-A-Bug II Concentrate
Bonide Eight Yard & Garden RTS1
Hi-Yield Total Pest Control-Outdoor Concentrate
Tiger Brand Super 10 Concentrate
Propiconazole Banner Maxx Fungicide
Ferti-lome Liquid Systemic Fungicide
Bonide Infuse Fungicide Concentrate; & RTS1
Pyrethrin Southern Ag Natural Pyrethrin Concentrate
Bonide Pyrethrin Garden Insect Spray Concentrate
Monterey Bug Buster-O
Spinosad Southern Ag Conserve Naturalyte Insect Control Concentrate
Bonide Colorado Potato Beetle Beater Concentrate
Bonide Captain Jack’s Dead Bug Brew Concentrate; & RTS1
Ferti-lome Borer, Bagworm & Leafminer Spray Concentrate
Monterey Garden Insect Spray Concentrate
Natural Guard Landscape & Garden Insecticide RTS1
Tau-fluvalinate Bayer BioAdvanced 3-in-1 Insect, Disease & Mite Control Conc.
Thiophanate-methyl Cleary’s 3336 Turf & Ornamental Fungicide
Southern Ag Thiomyl Systemic Fungicide
1RTS = Ready to Spray (hose-end applicator)
Drench = Add to water and pour around base of plant
Note: As with all pesticides, read and follow all label instructions and precautions.

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

More Problems

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

By Jeanne Lawrence, UC Master Gardener of Butte County, June 29, 2018

Viburnum opulus (snowball viburnum) It may be too hot outside to even think about putting new plants in the ground, but it’s always a good time to take stock of the garden. Are there aging plants that need replacing? Do you have an open area for a large, attractive shrub? Are you thinking about planting a hedge to provide privacy or screen out a less-than-desirable view? Would you like to have flowers to bring indoors for floral arrangements in the spring? If you can answer “yes” to any of these questions, you should think about planting one or more species of Viburnum.

The genus Viburnum comprises over 150 evergreen and deciduous shrubs and small trees, many of which do very well in our Butte County environment. In addition to providing structure and interest to the home garden, many viburnums are drought-tolerant and often provide fruits for birds to feed on. Some species produce highly fragrant flowers. And deciduous viburnum species can add lovely fall color to the garden before their leaves drop.

The following are just a few of the Viburnum species that do particularly well in our area.

Viburnum tinus (Laurustinus). This evergreen shrub is fast-growing in full sun or partial shade and creates a dense hedge of leathery oval, dark green, two-to-three-inch-long leaves. Allegedly only growing to 12 feet, examples have been spotted in Chico that easily reach 15 ft. or more. In early spring, tiny pink buds open up to clusters of white flowers that are long-lasting and fragrant; when the flowers finally drop, they are followed by equally long-lasting clusters of blue/black fruits that are loved by birds and may hang on until summer. V.tinus can be kept tidy by pruning, but if the possibility of a 15-foot hedge alarms you, dwarf and compact varieties are available.

Viburnum davidii foliage Viburnum carlesii (Korean Spice Viburnum). This is a Viburnum for real lovers of scent in the garden. It has a looser growing habit than V.tinus, is considerably shorter, reaching 6 to 8 feet, and is deciduous. Its springtime blooms are similar to those of V.tinus, with the exception of being more powerfully scented, a lovely surprise in the springtime garden. V.carlesii is also a little more delicate, preferring part shade in our summer heat.

Viburnum davidii. For a lower-growing shrub that provides nice structure in front of taller plants, V.davidii is a good choice. It is evergreen, with large oval leaves of up to six inches. It prefers partial shade, and, if happy, can produce clusters of brilliantly-colored metallic blue fruit.

Viburnum opulus ‘Sterile’ (Common Snowball). Deciduous in colder climates, V.opulous is nearly evergreen here. A taller Viburnum, it can reach up to 15 feet, but is easily kept in bounds. Its leaves are lighter green and maple-shaped. In spring it has snowball-like flowers clusters about two-and-a-half inches across, which start out lime green and turn to white. The flowering stems make a spectacular display as cut flowers indoors. This Viburnum bears no fruit.

Doublefile Viburnum Viburnum plicatum tomentosum (Doublefile Viburnum). This is perhaps saving the best for last, as the Doublefile may be the most stunning viburnum in the landscape. It is deciduous, but that is all the better for displaying its beautiful tiered growth habit – the branches move outwards in a series of almost parallel horizontal layers, clearly evident as soon as the new shoots begin to appear in spring. In late spring and early summer, white lacecap flowerheads two-to-four inches across line the upper sides of the branches. The flowers eventually give way to red fruits which turn to black. In the fall the leaves turn a pale shade of red, accented by brighter or pinker tones.

These are just a few of the interesting shrubs in this hard-working genus. If you have space for a new shrub, think about adding a viburnum to your garden.

For more information on gardening in our area, visit the Butte County Master Gardener web page at: http://ucanr.edu/sites/bcmg/. If you have a gardening question or problem, call our Hotline at (530) 538-7201 or visit ucanr.edu/p/49588.

ucanr.edu/p/49588

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