Boxwood Blight Returns to U.S. Nurseries

The boxwood is often referred to as “man’s oldest garden ornamental.” The boxwood, which has been planted in European and North American gardens since the mid-1600s, is popular because it can be used in hedges and groupings or as an individual specimen. Until recently, it was also easy to maintain and relatively disease free[1]. Unfortunately, boxwoods are now under threat.

Boxwood Blight

In 2011, the fungus responsible for boxwood leaf drop (Cylindrocaladium boxicola) was first detected in the United States. Though present in the U.K. since the mid-1990s, the spread of boxwood blight was initially controlled by careful quarantine of imported plants. That quarantine failed in 2011 when boxwood blight was identified in North Carolina and Connecticut. At the time, AmericanHort led an industry-wide effort to control the disease. Though initially successful, control measures have now failed. In the spring of 2015, boxwood blight was detected in Oregon. Unfortunately, plants had already been shipped to Alabama, Missouri, Ohio, Pennsylvania, and South Carolina before the fungus was identified. At least some of the plants in Ohio are thought to have been sold into the community[2].

Spread

Cylindrocaladium boxicola is a hearty fungus that is spread through rainsplash, contaminated tools, contaminated workers, and animals that come into contact with it. The fungus can also spread very short distances on the wind as well as by movement of plant debris such as fallen leaves (can survive up to five years on fallen leaves)[3]. Primary spread through Europe was by the movement of infected plants, cuttings, and debris.

Symptoms

Common symptoms of boxwood blight include circular leaf spots with a darker (brown or purple) margin as well as black steam lesions. The latter appear as dark streaks on the stems of plants and are typical of the blight.

Because boxwood blight is being treated as a “buyer-be-ware” infection, it is important for nurseries and land managers to assess all imported materials carefully. Plants treated with fungicide, which masks symptoms but does not cure blight, may appear to be uninfected. Plants do not need to be wounded or injured in order to become infected.

Control

Disposal of infected plants is the only way to be rid of the fungus. Because Cylindrocaladium boxicola is highly virulent, chances of an infected plant contaminating others is quite high. When boxwood blight is identified, the plant should be immediately bagged before it is moved or touched. Additionally, anyone handling the plant should be aware that the fungus is often transported on shoes and clothing.
To reduce spread of the fungus,

• Disinfect tools frequently (10 second dip in 70-100% ethyl or isopropyl alcohol),
• Never work in fields when plants are wet,
• Wear disposable booties and wash all debris/dirt from clothing
• Consider wearing Tyvek suits or laundering clothes between different plant blocks
• Burn or bury blighted plant material (do not compost), and
• Never discard boxwood waste where it could come into contact with other boxwoods[4].

Resources

[1] “About Boxwood.” [Online]. Available: http://www.boxwoodsociety.org/abs_about.html. [Accessed: 25-Aug-2015].

[4] K. Ivors, “Prevention and Management of Boxwood Blight,” Dept. of Plant Pathology, NC State University, Jan. 2012.