Rare Garden Plant Diseases: Boxwood Blight

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best landscape design firms and landscape management companies typically associate with top tier growers to maintain consistent quality in the plant materials they specify for your garden. Although growers cultivate new varieties of disease-resistant, high-quality garden plants each year, extreme weather conditions can cause problems with even the hardiest of nursery stock.

Following an unusually wet summer and autumn, the relentless weeks on end of damp and cloudy weather (65 days to be exact) created conditions perfect for setting off an outbreak of boxwood blight.

Boxwood: What It Is and Why It’s So Popular

Boxwood is probably the most ubiquitous garden ornamental plant found in Northern Virginia landscapes. Surrounds Landscape Architect Howard Cohen calls it a “timeless classic.” It is prized by Cohen and other landscaping professionals for its versatility: Boxwood, because it naturally grows in a variety of silhouettes and sizes, can be put to service as a hedge, foundation planting, or as an edging plant.
Robert Saunders of Saunders Brothers Nursery goes further, calling it “the aristocrat” of landscaping plants. A significant portion of Saunders Brothers annual nursery production is devoted to boxwood varieties because of its utility, longevity, and deer resistance.

Over the past sixty years, the grower has invested considerable resources to support research into the characteristic strengths and vulnerabilities of boxwood. This dedication makes Saunders the go-to source for information about the developing boxwood blight situation in Virginia.

What Causes Boxwood Blight?

Landscape designers try to select garden plants with the best track record regarding pest and disease resistance. In truth, almost all garden plants come with an attendant set of diseases and insect pests that prey upon them. Often, the damage wreaked by these invaders is merely unsightly.

However, some plants diseases can be deadly if they aren’t properly contained and are allowed to spread throughout a landscape. One such rare and fatal plant disease is boxwood blight. This fungal infection springs to life and spreads quickly during prolonged periods of the day and night temperatures between 60-70 degrees combined with abundant rainfall and high humidity.

Although boxwoods are characteristically resistant to most diseases, boxwood blight is their Kryptonite. Boxwood blight attacks all boxwood cultivars but is lethal when contracted by English boxwood.

Here are some key points about the disease adapted from Saunders Brothers 5th Edition Boxwood Guide:

• Originated in Europe and made its first documented U.S. appearance in 2011
• The fungus develops rapidly in prolonged wet weather with little air movement
• Fungal spores spread from plant to plant by contact with people and garden equipment, or by splashing water (rain or irrigation)
• The blight goes dormant in dry conditions combined with either very hot or very cold temperatures—but returns when conditions are right
• The disease can survive for up to five years in infected debris—so thorough clean-up is crucial
• It is essential to remove all contaminated plant material, debris, and soil

How to Recognize Boxwood Blight & What to Do About It

When hiring landscape firms to clean up infected plants, it is important to hire reputable firms who are educated on the disease and take steps not to spread the disease to other landscapes. Saunders Brothers Nursery

Boxwood blight presents as brown spots on the foliage that darken to nearly black before falling off. You’ll also see black streaks on the stems. The plant will continue trying to put out new leaves, but repeated defoliations will kill it.

The best landscape management companies practice integrated pest management (IPM). There are two cornerstone principles that IPM employs to protect your landscape:

1. expert plant selection and plant care practices to suppress disease and pest activity in lawns and gardens
2. frequent visits to the property to ensure that disease or pest issues, when they do occur, are identified and correctly treated before widespread damage occurs.

The hard truth is that even with the best landscape maintenance and garden care, boxwood blight can spread quickly over the entire property. If you should notice something suspicious developing between service visits, contact your landscaping company immediately.

Please do not attempt to remove infected materials yourself for risk of spreading the disease.

A horticulturalist from your landscaping company will come out and inspect, bag some samples, and send them to the Cooperative Extension for testing. Once they are sure about what they are dealing with, they can discuss an appropriate action plan with you.

For boxwood blight, the treatment is pretty drastic. Saunders Brothers recommend complete removal of the infected plant and adjacent boxwoods. The decision to remove/replace plants is best left to your landscape management company because they have the horticultural expertise to devise the best course of action.

If you suspect that your boxwoods or other landscape plants may be fighting some type of disease or pest infestation, contact one of our horticulturalists to schedule a phone consultation.