Boxwood Blight is NOT a death sentence for affected plants. STOP ripping ‘em out!
What Is Boxwood Blight?
Boxwood Blight is a fungal disease that if left untreated can cause severe and extensive damage to your boxwood. The disease can spread quickly, when optimal conditions exist, and the fungus is present.
The disease is caused by the fungal pathogen Calonectria pseudonaviculata (previously called Cylindrolcadium pseudonaviculatum or Cylindrocladium buxicola). Boxwood Blight affects plants in the Buxaceae family which includes Boxwood (Buxus), Sweetbox (Sarcococca) and Pachysandra.
The disease was first reported in the United Kingdom in the mid-1990s. It’s now widespread throughout Europe and was also discovered in New Zealand in 1998. Since first identified in the United States in 2011, Boxwood Blight has been found in 28 states coast-to-coast and in 3 Canadian provinces. It’s unknown how the pathogen was introduced to the United States, but it likely traveled on infected plant material.
How to Identify Boxwood Blight
Boxwood Blight first attacks the foliage or leaves of boxwood appearing as black or dark brown spots on the leaves (Figures 1 & 2). Those spots will develop yellow or brown rings around them and cover the leaf. During periods of high humidity, if you look on the undersides of infected leaves, you will see white sporulation of the Boxwood Blight fungus.
A key symptom that differentiates Boxwood Blight from other boxwood diseases is the narrow black streaked lesions or cankers that develop on green stems near infected leaves (Figure 3). During periods of high humidity, white, fuzzy masses that consist of numerous clumps of spores will emerge from these black stem cankers. The spores can be observed on infected stems and leaves with a hand lens.
Boxwood Blight causes rapid defoliation, which usually starts on the lower branches and moves upward in the canopy (Figure 4).
Optimal Conditions for Boxwood Blight
The optimal conditions for this disease include damp areas with little air movement around 60-80º F and high humidity. Leaves that are continuously wet from constant irrigation, prolonged rain, or high humidity are prime targets for the Boxwood Blight pathogen. In non-optimal weather conditions (i.e., prolonged dry, hot, or cold weather), the fungus goes dormant. Blight disease can reside in the stems of boxwood or in debris on the ground in an inactive state for long periods of time and reappear when the conditions are optimal again.
Prevention & Control
Boxwood Blight is best avoided by applying Best Management Practices that will keep your boxwood healthy and looking great all year long.
Educate Yourself And Others About Boxwood Blight
Start With Healthy Superior Boxwood
“The first and best defense against plant diseases is a healthy plant.”¹ Use reputable commercial nurseries, landscapers, tree and lawn care companies, who are aware of Boxwood Blight and take the necessary steps to avoid introducing or spreading the disease in your landscape.
Fertilize Your Boxwood From Top To Bottom
“A properly nourished plant is able to withstand or tolerate the attack of pathogens much better than a plant that has either nutrient deficiencies or excesses. A nutrient-deficient plant will be stressed and therefore more prone to disease attack.”² Just as your lawn requires regular fertilization for overall health, vitality and beauty, so does your boxwood. To optimize the health of your boxwood, fertilize the top of the boxwood leaves to provide proper amounts of nutrients for strong growth and intense green leaves. Spray the boxwood with a foliar leaf fertilizer such as TOPBUXUS® Boxwood Restore & Protect Mix, thoroughly covering the leaves until they are slightly dripping.
Fertilize the bottom of the boxwood, its root system as well. Fertilizing the boxwood root system helps increase the nutrient uptake to the stems and to the leaves encouraging continued healthy green growth. Boxwood have wide, shallow root systems and can be damaged by over fertilization. Place the fertilizer near the dripline of the plant and keep the fertilizer from coming into direct contact with the leaves, trunks, and roots. TOPBUXUS® Boxwood Turbo Grow is a fast acting granular fertilizer and an ideal application for the boxwood root system.
Mulch Underneath And Around The Boxwood Plant
Mulch annually with a thin layer approximately 1 to 2 inches thick and just in front of the dripline to about 8 inches beyond the dripline of the boxwood. Recent research has shown the value of properly mulched boxwood in the management of Boxwood Blight.
Prune Boxwood In Dry Weather
Don’t prune your boxwood when the plant is wet or in high humidity. Water and humidity promotes optimal conditions for Boxwood Blight to appear and increases the likelihood of spreading the infection. Proper pruning helps increase the airflow and sunlight penetration under and around the plant ensuring proper leaf drying.
Collect and remove boxwood debris after pruning or shearing that involve infected plants. Make sure not to compost the debris so you will lessen the spread of the disease. The debris should be bagged for municipal waste.
Clean Shears And Pruning Tools
Clean your tools and equipment each time you use them with Lysol Disinfectant Spray for Commercial Use with 58% ethanol and 0.1% dimethylbenzyl ammonium saccharinate. A mixture of household bleach ratio of 1:9 is another alternative, but it does corrode and pit metal tools. After spraying your tool, air dry it for 5 minutes before using it again. Boxwood Blight spores can spread from plant to plant, on clothing, tools and equipment, or splashing water. Once you are finished pruning, make sure you launder your gardening clothes immediately.
Water Boxwood Properly
Avoid overhead or excessive watering or working with boxwood when it’s wet from rain, irrigation or dew. You may want to use a soaker hose or a drip irrigation system. Implementing an irrigation schedule that allows time for the leaves to dry can significantly reduce the spread of disease.
Provide Adequate Drainage
Boxwood plants need to be planted in well-drained soil and at the proper depth. This helps reduce stress and root disease issues.
Routinely Monitor And Inspect For Boxwood Blight
Inspect all boxwood plantings in the landscape throughout the growing season. If you observe suspicious symptoms on your boxwood, it’s important to have the disease accurately identified by a specialist. Once Boxwood Blight is confirmed, follow the Best Management Practices to lessen and stop the infection.
Keep your plants healthy by applying Best Management Practices for boxwood. “With proper plant care, you can limit the amount of stress your plants suffer and the likelihood that they will develop certain infectious and non-infectious diseases.”³
A healthy plant is the best practice for preventing Boxwood Blight!
Volutella, The Other Boxwood Blight
Volutella Blight disease is caused by the fungus Volutella buxi (Pseudonectria buxi) and affects the leaves and stems of the plant. The Volutella blight produces salmon pink colored fruiting bodies on the underside of the leaf (Figures 5 & 6). Volutella is a disease that can affect plants that are stressed or weak.
The first sign of Volutella Blight on boxwood is visible in the spring with poor growth on individual shoots or on the entire plant. Affected leaves turn from green to red, then finally to a straw and tan color as the disease progresses (Figures 7 & 8). You will often see black streaks or cankers on the 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 salmon pink colored spores on the lower surface of the foliage. Also, the bark on affected plants becomes girdled, loose and can easily peel away.
How to Identify Volutella Blight
Prevention & Control
To prevent or control Volutella Blight, apply the same Best Management Practices for Boxwood Blight. The only exception in practice is when you are pruning diseased branches:
Pruning Diseased Branches When Volutella Blight Is In The Early Stage
The boxwood leaves will be green-red/bronze in color. You don’t have to prune out the infected branches.
Pruning Diseased Branches When Volutella Blight Is In The Later Stage
The boxwood leaves will be straw to tan in color. When the leaves are straw to tan in color, the branches are most likely dead. Prune out the diseased branches. Collect and remove the diseased branches by bagging them and disposing of the bag. Do not compost diseased branches.
- Patricia Hosack and Lee Miller, ‘Preventing and Managing Plant Diseases’, University of Missouri Extension Division, Division of Plant Sciences, July 2017, https://extension.missouri.edu/publications/mg13, (accessed 27 February 2021).
- Stephen A. Ferreira, ‘Management Practices to Prevent and Control Plant Diseases’, College of Tropical Agriculture & Human Resources University of Hawaii at Manoa-Extension Service, CTAHR, Plant Pathology Department, October 1998, https://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-14.pdf, (accessed 27 February 2021).
- Jim Chatfield, ‘Nine Keys to Plant Disease Prevention’, Brooklyn Botanic Garden, September 2000,https://www.bbg.org/gardening/article/disease_prevention,(accessed 23 February 2021).