How to Identify Boxwood Blight

Boxwoods are a genus of around 90+ species within the Buxaceae family, with new varieties hitting the market every year. They are broadleaf evergreen shrubs that are a staple of many landscapes and grow in a variety of climates. Used as foundation plantings, hedges, and more, they require part or full sun depending on yearly climate for optimal growth.

Boxwoods are typically low maintenance, unless they are used as a formal hedge and need regular shearing. However, they can become diseased, most commonly with blight and Phytophthora. These diseases can look similar. Use our guide below to help identify boxwood blight.

Identifying Boxwood Blight

Boxwood blight is a fungal disease caused by Calonectria pseudonaviculata and C. henricotiae that affects Buxus, Pachysandra and Sarcococca genuses. Research states a wide range of boxwood cultivars are susceptible to boxwood blight, but the most susceptible species are B. sempervirens with Buxus sempervirens ‘Suffruticosa’ (English boxwood) and Buxus sempervirens ‘American’ (common or American boxwood) topping the list.

Originally discovered in the United Kingdom in the 1990’s, boxwood blight came to the United States in 2011. This disease has now been found in 23 states. As shown in the above image, it significantly impacts the plant’s aesthetics and eventually kills the plant. Symptoms include leaf spot, rapid defoliation, severe dieback, and black cankers on stems. Circular leaf spots appear before leaf blighting, and the spots often look brown or purple. You may also notice dark brown or black stem lesions. In areas of high humidity, you might notice white fuzzy masses of spores on stems and leaves, but this is less common. It can take over quickly during wet periods and can go dormant in warmer and drier conditions, only to reappear when the weather changes.

Avoiding Blight

The fungal spores can last over 10 years in the soil. They stick to anything exposed to the infected plant, such as gloves, tools, equipment, tires, clothes, and more. Some states, such as Pennsylvania, Virginia, and Tennessee now have Boxwood Compliance Agreements to abate this infectious disease. The agreements contain strict protocols for boxwood shipping and care.

To limit infection rates, you should follow these guidelines.

• Make sure to purchase boxwood from reputable suppliers.
• Water the plant roots (not leaves) in the morning, as evenings can have low temperatures and fungus thrives on wet leaves.
• Clean your tools in a 10% bleach solution after pruning different blocks of plants. Use a fresh solution after each job.
• Properly dispose of any infected plants, typically by burning the plant on-site.
• Do not work in landscape beds when the plants are wet.
• Consider using mulch around boxwoods to prevent water splash onto leaves, keeping them drier.
• Wash off shoes and clothing between landscaping jobs, especially in areas noted to have boxwood blight.
• Apply preventative fungicides regularly in areas noted to have boxwood blight.

If you suspect boxwood blight, quarantine the plants as soon as possible. Gather sample stems and leaves and take pictures. Take these pictures into your local SiteOne Nursery or your local state extension office to discuss your next steps and to inform them of the disease in the area.

If boxwood blight is prevalent in your area, consider asking your customer to choose a boxwood variety that is more resistant, such as Portfolio® Little Missy, Green Gem, Winter Gem, or Dee Runk. Other alternative plants are Ilex glabra and Ilex crenata, which mimic the boxwood look without the disease pressures.

Monitor your clients’ plants when doing preventative maintenance and pruning to avoid costly spread of disease.

SiteOne associates can help you with any questions or concerns you may have. If you need replacement plants, consider shopping at a SiteOne Nursery or using our Nursery Direct program.