Volutella Blight Boxwood Treatment: Learn About Volutella Blight Control

Volutella Blight Boxwood Treatment: Learn About Volutella Blight Control

By: Mary H. Dyer, Credentialed Garden Writer

Boxwoods are attractive evergreen shrubs that retain their emerald-green color year round. Unfortunately, boxwoods are susceptible to a variety of diseases, and a fungal disease known as volutella blight on boxwood is one of the worst. Read on to learn about volutella blight control.

Symptoms of Volutella Blight on Boxwood

The first sign of volutella blight on boxwood is delayed and stunted growth in spring, typically followed by die-back of branches. Leaves turn yellow, darkening to tan as the disease progresses, often with black streaks on the petioles (small stems that join the leaves to the branch).

Unlike healthy leaves that spread out, leaves affected by volutella blight remain close to the stem. If conditions are wet, you may notice masses of pinkish spores on the lower surface of foliage. Bark of affected plants peels away easily.

Volutella Blight Control and Prevention

To control or prevent this disease, the following precautions should be taken:

  • Ensure boxwoods are planted in well-drained soil with a soil pH between 6.8 and 7.5.
  • Spray boxwood with a copper-based fungicide before new growth emerges in spring, then spray again immediately following pruning, and again in summer and autumn. Spray carefully to penetrate the thick foliage. Remember that fungicides can be an effective preventive measure, but they are not a cure.
  • Water boxwood as needed to keep the soil evenly moist but never soggy. Avoid overhead watering. Instead, water at the base of the plant, using a garden hose, drip system or soaker.

Volutella Blight Boxwood Treatment

Sanitize pruning tools before and after each use. Use sharp tools to prevent scratching and tearing plant tissue. Prune the diseased boxwood to improve air circulation, light penetration and overall growing conditions. Remove all dead growth, including leaves that are caught in the crotch of branches.

Work carefully; pruning wounds provide an entry point for the disease. Prune only when the plant is dry, as pathogens spread quickly in damp conditions.

Rake up all debris under the plant after pruning, then burn diseased debris immediately to prevent spread of the disease. Alternatively, dispose of debris in a tightly sealed plastic bag. Never compost diseased plant material, and keep in mind that fungus can live in the debris for as long as five years.

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Home Yard & Garden Newsletter at the University of Illinois

With the recent detections of boxwood blight in Illinois, the importance of scouting landscapes and new plants for the disease is greater than ever. Boxwood blight can be a challenging disease to identify outside a plant diagnostic laboratory. Many of the symptoms associated with the disease are similar to other common boxwood disorders. One major difference between boxwood blight and its look-alikes is the potential for defoliation. Boxwood blight causes extensive defoliation, while look-alike disorders tend to have leaves turn tan to brown, but remain attached to the plant. A microscope is needed to confirm the disease diagnosis. Some of the common boxwood blight look-alikes include winter Injury, Macrophoma leaf spot, Volutella blight, Phytophthora root rot, Fusarium canker, boxwood leafminer, and potentially boxwood psyllid. Fortunately, these look-alikes cause a relatively minor injury that can be pruned out during a dry period of spring weather.

Boxwood blight is a regulated plant disease in Illinois. If you suspect this boxwood blight, we recommend you contact the University of Illinois Plant Clinic for information on how to submit a sample. Never take a suspected boxwood blight sample to a garden center, nursery, or other areas that may grow or distribute boxwood. While these businesses may offer plant advice as a service to their customers, they are extremely cautious and go to great lengths not to introduce or spread this disease.

Winter Injury (Abiotic)

Winter injury occurs as cold, dry winter winds and/or direct sunlight causes moisture loss from the evergreen leaves. Frozen soil prevents the plant from taking up water resulting in “freeze-dried” burn symptoms. Depending on a plant’s hardiness, location, and the weather conditions, winter injury can damage the entire plant or just the branch or leaf tips causing leaves to become pale yellow/reddish bronze. The pattern of injury can also help diagnose winter injury. Injury is most likely to occur southwest and windward facing sides of the plant. A “snow line,” or distinct line that separates the healthy green bottom from the damaged brown top can also be an indication of winter injury. Snow insulates and protects foliage from desiccating winds and extreme cold temperatures.

Macrophoma Leaf Spot (Macrophoma candollei)

Macrophoma is a weak pathogen that causes leaf spots and straw-colored leaves. The disease can easily be identified by the numerous black, raised fruiting bodies found on dead or dying leaves (Photo 1).

Photo 1. Black, raised fruiting bodies of Macrophoma Leaf Spot on boxwood.

Volutella Blight (Volutella buxii (asexual stage of Pseudonectria rouselliana))

This fungal pathogen is often associated with stem and leaf tissues damaged from winter injury. Infected leaves turn tan, straw-yellow or bronze color in the spring. Volutella progresses down the stem, whereas winter injury happens seemingly at once. Under moist, humid conditions, the foliage may develop distinct masses of pink to salmon colored spores (Photo 2).

Photo 2. Volutella Blight with salmon colored sporulation.

Phytophthora Root Rot (Phytophthora spp.)

Heavy, wet soils favor Phytophthora root rot. There are many species of Phytophthora, some of which have a broad host range. In boxwood, Phytophthora can cause individual branch wilting and dieback leaving isolated areas of pale green, then brown, shriveled leaves attached to the stems. Roots are often dark brown or black, sparse, and brittle, and the cambium (inner tissue under the bark) at the base of the main stems may also become discolored dark brown or black. Management consists of removing infected plants available chemical control is best used as a preventative, but does very little once an infection has been established. Boxwood beds should be well drained and overwatering avoided. If a plant is removed due to Phytophthoraroot rot, avoid planting other susceptible plants in that area. Symptomatic boxwood plants can be tested for Phytophthora, however root or base tissue is needed. If multiple plants are affected and you are concerned about replanting, you may want to consider digging up an entire plant to submit to the Plant Clinic.

Photo 3. Phytophthora root rot showing light green, wilting leaves followed by leaf death. Image credit: Neil Bell, Pacific Northwest Pest Management Handbooks.

Fusarium Canker (Fusarium spp.)

Fusarium cankers on boxwood do not appear to be common in the landscape. At the Plant Clinic, we have only seen them on samples submitted from nurseries or greenhouse producers. We suspect this is due to cultural conditions in the nurseries (plants situated close together, high humidity from overhead watering or plentiful irrigation) which favor the development of this disease. In our experience, fusarium cankers are more commonly found at the tips of branches (Photo 3) compared to boxwood blight, which may be found near the base or the middle of branches. Fusarium cankers appear as dark brown or black streaks along boxwood branches that quickly coalesce into contiguous patches of discolored tissue. These cankers appear very similar to those caused by boxwood blight, and both may cause defoliation. Because of this, individual spores of the pathogen must be observed under the microscope to differentiate between the two. This is yet another reason to have the disease confirmed by a diagnostic laboratory.

Photo 3. Fusarium canker affecting the tips of branches.

Boxwood Leafminer(Monarthropalpus buxi)

Boxwood leafminer causes off‐green pouches on leaves that turn brownish as the larvae
Mature (Photo 4). Because partially‐grown larvae overwinter, heavily affected leaves develop light brown mottling in the spring when other foliage is green. This mottling occurs on both the under‐ and uppersides of the leaves.

Photo 4. Boxwood leafminer damage.

Boxwood Psyllid (Pyslla buxi)

Boxwood psyllids are small (1/16-inch), grayish green insects that are normally covered with a white, waxy, filamentous secretion that partially covers the body, providing protection from parasitoids and sprays of pest-control materials. Eggs overwinter and hatch into yellowish nymphs that begin feeding as soon as buds begin to open in early spring. The first-instar nymphs feed by sucking plant fluids from terminal leaves as they unfold and expand in spring. Their feeding causes leaves to yellow, curl, and form a cup (Photo 5), which conceals and protects the nymphs. There is one generation per year.

Photo 5. Boxwood psyllid damage.

What are some methods to deal with box blight?

Box blight hedge treatment is a long and difficult task but, with patience and dedication, it can be done.

Although, if the disease is too widespread, it may be best to destroy the infected plant and cultivate a healthy replacement instead.

Before we get started, there are measures you should take when treating box blight to reduce the chances of the infection spreading.

    Clean the tools when you are finished using them. You can use diluted household bleach, or methylated spirits. Wash the clothes you were wearing when tackling the infection. Remove any leaves or soil from the soles of your shoes.

Now that we’re ready, let’s move on to the box blight cure.

Step one. Taking back control.

Since box blight attacks the leaves and stems of plants, the first task is removing the infected areas to stop the disease from spreading. It is vital that you do this during a dry period. If you prune the infected areas while the plant is wet or there is rain forecast, the disease will spread rapidly. Knowing how much of a plant to remove can be tricky in a lot of situations but, with box blight, there are three straightforward options. Which option you choose depends on the severity of the infection.

For easier clean up later, place a plastic sheet around the bottom of the plant you’re saving.

Option one.

If you have noticed the infection during the early stages, this is the option for you. Simply cut the infected stems back until they are brown on the outside and vivid green beneath the bark. Once you reach the healthy parts of the plant, cut it back a little bit more.

Option two.

When faced with a large-scale infection, the best course of action is to reduce the height of the plant by half, or until there are no blackened stems.

Option three.

If the infection is too severe and you don’t want to replace the plant, the only option is to cut the entire plant down until it is just a stump. Regardless of which option you choose, when you’re finished pruning, it is a good idea to spray the remainder of the plant with a fungicide to kill off any lingering spores. There are also some box blight commercial treatments available. These specialised fungicides are perfect if the affected areas are too small to prune.

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Step two. The clean-up.

  • Remove any severed stems or leaves that are trapped inside the plant. The dead leaves around the base of the plant provide a perfect breeding ground for fungi, so clear away all of the leaves under and around the plant. Be meticulous as it doesn’t take many leaves to restart the infection. Spores from either type of fungi are capable of surviving in the soil for an astoundingly long time. Because of this, you will have to remove and replace a layer of soil from around and under the plant.
  • Disposal of infectious materials. Once you’ve collected all of the infected plant cuttings and leaves, you’ll need to get rid of them. The best method of disposal is to burn all of the cuttings but, if you are unable to burn them, you can seal them in a bag and put it in the bin. You should avoid adding any of the infected plant parts to your a compost heap or the council recycling composting bin under any circumstances. This will only spread the fungus spores over a wider area.

And don’t forget to clean your tools.

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Diagnosing and Treating Boxwood Blight

Boxwoods are the go-to shrub for many homeowners that want an attractive living boundary around some part of their property. The slow-growing evergreen shrub makes a lovely and long lasting hedge row that is easily maintained, unfortunately it can be wiped out very quickly by a terrible disease called Boxwood Blight.

Signs of Boxwood Blight

This blight that infects both boxwoods and their ground-covering cousins, the pachysandras, is caused by a fungal organism known as Cylindrocladium buxicola. The disfiguring organism is also called Cylindrocladium pseudonaviculatum or Calonectria pseudonaviculata.

Boxwood blight will first manifest itself on the leaves of the evergreen shrub (other evergreens are not in danger from the blight, only boxwoods and pachysandras). Small brown spot will appear on the leaves and soon thereafter those spotted leaves will fall off the shrub. The branches which the leaves were on will begin to die next. The remaining leaves on the shrub will turn yellow and plant growth will cease. The shrub will take on a deformed and disfigured appearance and a once neatly shaped row of boxwoods will look as though they have been through a fire.

The Best Defense

Since there is currently no known cure for boxwood blight, a defensive treatment to prevent the blight is the best course of action. Follow the precautions when working on your boxwoods or pachysandras.

* Start by planting boxwoods and pachysandras in a sunny location, never in a shady location.

* Stay away from the shrubs when they are wet. The wet shrubs are at a weakened stage and more susceptible to attack from a fungus.

* Disinfect your pruners between plants by dipping them in a solution of nine parts water and one part bleach for 10 seconds. Scrub them thoroughly with soap and water and dry them before putting away after pruning is completed.

* Always destroy or dispose of boxwood clippings. Never compost them unless you are sure your shrubs are disease-free.

* Clean off the soles of your shoes before moving from one part of the garden to another. To easily and quickly clean shoe soles, wear rubber or plastic garden shoes or boots, then dip them into the bucket of disinfecting solution used for the pruning shears. Dip them for 10 seconds, then dry the soles on an old cloth before continuing through the boxwoods or pachysandras.

The evergreen boxwood plants that we offer here at GreenwoodNursery.com have shown resistance to the Boxwood Blight disease.

Read our article with more detailed information on What is Boxwood Blight.

MSU Extension Landscaping

Heidi Lindberg, Michigan State University Extension Jan Byrne, MSU Plant & Pest Diagnostics Monique Sakalidis, MSU Departments of Plant, Pest, and Microbial Sciences and Forestry and Elizabeth Dorman, MDARD - September 10, 2019

While the browning and defoliation of boxwood is a key symptom of boxwood blight, there are a number of other look-alike plant problems.

Winter damage on boxwood is often confused with boxwood blight. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.

Since boxwood blight has been found in Michigan for the first time in summer of 2018, growers, landscapers and consumers alike are concerned that their boxwoods could have boxwood blight. It is a legitimate concern because the disease has been found in Michigan and 27 other states. Boxwood blight (Calonectria pseudonaviculata) is a fungal pathogen of species in the plant family Buxaceae, which includes the popular boxwood, sweetbox and Pachysandra spp.

In boxwood, often the first symptom noticed is a large amount of rapid defoliation (leaf drop), which is indicative of a severe infection. Generally, part of the plant will become chlorotic or brown, and leaves will rapidly fall to the ground, leaving bare branches behind. Initial symptoms are generally first observed in late spring or early summer when close examination of boxwood leaves may reveal round, dark or light brown leaf spots with darker borders and potentially a yellow halo. These spots eventually grow larger and coalesce before turning brown or straw-like and dropping to the ground. Black, elongated, streaking lesions may also be visible on the stem. These can occur on the stem from the soil line to the shoot tips. If the weather is humid, the underside of the leaf will have a white, frosty appearance caused by the formation of upright bundles of fungal spores. For pictures of these symptoms, see “Preventing the spread of boxwood blight in landscapes.”

However, there are numerous reasons for defoliation and browning of boxwood plants. Here are seven common aliments of boxwood plants.

Winter injury

Winter injury is the most common problem that affects boxwood. It becomes apparent as the snow recedes and the uppermost or outermost leaves and stems on the boxwoods are brown. Buxus sempervirens is typically hardy down to USDA Zone 5. Plants are especially susceptible to winter damage in temperatures below -10 degrees Fahrenheit, especially in locations next to pavement or siding of the house with direct sunlight that warms the tissue up too quickly. Winter damage is especially distinctive in that the growth below the former snowline is still green. As long as the damage is not overly severe, growers can just prune out or prune off the damaged foliage.

Winter damage of boxwoods on the outermost growth and growth that was above the snowline. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.

Salt damage

Salt used for sidewalks and roadways can cause damage to boxwoods. First, the spray of the salt water on the foliage can cause the plant to desiccate in those tissues, killing the leaves on one side of the plant. Excessive salt washed into the soil can also change the water uptake of the plant, causing salt damage. In these cases, it is most identifiable when there is a pattern where the boxwoods closest to walking surfaces show the worst damage. It is also noticed in spring.

Salt damage on boxwoods at a residential landscape. The plant closest to the stairs to the porch show the most severe injury. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.

Drought stress

Boxwoods, like other plants, can show drought stress by the browning of foliage. Drought stress is the most severe in newly-planted landscapes where the plants are suffering from transplant shock, those without irrigation or rainfall for a long period of time, or those grown in very warm temperatures. The symptoms of drought stress are typically browning of the center of leaves and chlorotic foliage.

Drought stress of boxwood plants can cause the yellowing and necrosis of foliage. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.

Boxwood leafminer

Boxwood leaves can turn brown from the boxwood leafminer. The adult leafminer (a mosquito-like fly) lays its eggs between the layers of the leaf and the developing larvae feeds on the tissue. The adults emerge from the leaves, leaving an emergence hole where they exited. The infested leaves will develop brown patches as the larvae grow and heavily infested leaves will defoliate in the late fall and early spring.

Boxwood leafminer larvae feed on the inner tissue of boxwood leaves causing the browning of leaves of boxwood plants. This is distinguishable since there is often an emergence hole or a larva of the leafminer inside the leaf. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.

Volutella stem canker

In addition to abiotic problems and insect damage from boxwood leaf miner, boxwood is also susceptible to Volutella, a fungal pathogen caused by Pseudonectria buxi. Prior to the new growth in spring, the leaves will bronze and yellow. The fungus produces salmon/pink fruiting bodies when it is sporulating on the undersides of the leaves. On infected branches, the bark can become loose and they may dieback. It often causes the complete death of part of a plant.

Moist weather is conducive to the development of Volutella infection. One distinguishing difference between boxwood blight and Volutella is that the fruiting bodies or sporangia of boxwood blight are gray-white while they are pink-salmon for Volutella. In addition, the leaves do not fall off of plants with Volutella as they do with boxwood blight.

The photo on the left shows the pink fruiting bodies on the underside of the boxwood leaf. The right photo shows the dieback of a heavily infested boxwood plant. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.

Macrophoma leaf spot

Boxwoods are also susceptible to Macrophoma leaf spot caused by the pathogen Macrophoma candollei. This parasitic fungal pathogen causes red-brown lesions on leaves and when sporulating has black fruiting bodies on the undersides of leaves.

Macrophoma leaf spot on boxwood leaves. Photo by Margery Daughtrey, Cornell University.

Phytophthora root and crown rot

Phytophthora root and crown rot can also cause the wilting and browning of the foliage on boxwood plants. The fungi Phytophthora spp. can cause plant stunting, yellowing of leaves, upward turning of leaves, death of root tissues and discoloration on the stem of the plant near the soil line. Leaves of plants infested with Phytophthora root rot do not have any fruiting bodies.

Dieback on boxwood plants from Phytophthora root and crown rot. Photo by Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org.

When looking at the boxwoods in your nursery or landscape, examine if there are any patterns to the damage and consider sending in a sample to get a confirmation by a diagnostic lab, such as Michigan State University Plant & Pest Diagnostics. These problems are often confused due to their similar symptomology. Diagnosticians will be able to help identify which of these common problems could be causing the plant damage.

For more information, check out “IPM Series: Boxwood” from University of Maryland Extension.

To learn more about preventing boxwood blight in commercial nurseries, check out “Preventing boxwood blight in nurseries” from MSU Extension, and for more information for landscapers and homeowners, check out “Preventing the spread of boxwood blight in landscapes.”

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Boxwood (Buxus spp.)-Volutella Leaf and Stem Blight (Canker)

Branches die back and leaves turn from green to light green-yellow and finally to shades of tan.

Cause Pseudonectria buxi (asexual: Volutella buxi ), a fungus that survives in affected branches and leaves. Boxwood is susceptible to infection when subjected to wounds or winter injury. Optimal temperature for infection and disease development is 68°F to 77°F when relative humidity is 85% or greater. Infection often occurs at the bases of small dead shoots, or in crotches where leaves have accumulated, or through pruning wounds. One-month-old leaves were much more susceptible than 1-year-old leaves.

Most common cultivars such as Green Velvet, Green Gem, Green Mountain and Chicagoland Green are susceptible. 'Pincushion' has exhibited less disease in inoculation tests and at nurseries in Ontario, Canada, but no cultivars are immune.

Symptoms Branches die back and leaves turn from green to light green-yellow and finally to shades of tan. Affected leaves turn up and lie close to the stem. Black streaks may be found on some petioles or on stems near petiole attachment. These symptoms are similar to winter injury, except that numerous, small, salmon-pink fungal spore-producing structures (sporodochia) appear on lower surfaces of affected leaves and branches.

  • Prune out and burn dead branches.
  • Remove dead leaves from crotches areas inside the canopy.
  • Minimize wounding especially when new growth is present.
  • Maintain good air circulation and drainage.
  • Avoid high humidity (>85%) for long periods.
  • Grow plants in well-drained media or soil with a pH between 6.8 and 7.5. Light shade of 20% can also reduce injury from summer and winter extremes.

Chemical control Spray fungicides in spring, before new growth starts, and again in late spring anytime wounded tissue may occur such as after pruning.

  • Banner MAXX at 2 to 4 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Bordeaux. O
  • Broadform at 4 to 6 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Cleary's 3336 EG at 12 to 16 oz/100 gal water plus another fungicide from another fungicide group. Boxwood is NOT specifically mentioned on the label but may legally be used. Group 1 fungicide. 12-hr reentry.
  • Concert II at 26 to 35 fl oz/100 gal water. Might leave a slight residue on leaves and/or slight plant growth regulation effect. For use in nurseries and some landscapes. Group 3 + M5 fungicide. 12-hr reentry.
  • CuPRO 5000 at 1.5 to 5 lb/A. 48-hr reentry.
  • Daconil Weather Stik at 1.4 pints/100 gal water. Do not use with a surfactant. Can be used in the landscape and many other sites. Boxwood is not on the label but may legally be used. Test first on a small section before applying on the whole plant to evaluate possible phytotoxicity. Group M5 fungicide. 12-hr reentry.
  • Dexter Max at 1 to 2.1 lb/100 gal water. Group M3 + 11 fungicide. 24-hr reentry.
  • Mancozeb-based products. Group M3 fungicides. 24-hr reentry.
    • Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
    • Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
  • Phyton 27 at 1.5 to 2.5 fl oz/10 gal water. M1 fungicide. 48-hr reentry.
  • ProStar 70 WG at 6 oz/100 gal water. Group 7 fungicide. 12-hr reentry.
  • Rex Lime sulfur at 0.5 gal/100 gal water after leaves are cleaned up. 48-hr reentry. H O

Reference Shi, F., and Hsiang, T. 2014. Pseudonectria buxi causing leaf and stem blight on Buxus in Canada. European Journal of Plant Pathology 138(4):763-773.

Watch the video: Qu0026A - Why are the leaves of my boxwood falling off?