Author Archives: Mary Ann Hansen

Update on Boxwood Blight in Virginia

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English boxwood defoliated by the boxwood blight pathogen following introduction of infected container plants on the patio. (Photo by A. Bordas)

English boxwood defoliated by the boxwood blight pathogen following introduction of infected container plants on the patio. (Photo by A. Bordas)

Recent outbreaks of boxwood blight, caused by the fungus Calonectria pseudonaviculata, are causing concern in Virginia. Boxwood blight can cause severe defoliation of susceptible boxwood, including English and American boxwood, and is of serious consequence to nursery growers, landscapers and homeowners. All diagnoses of boxwood blight in home landscapes made by the Virginia Tech Plant Disease Clinic since last fall are linked to new boxwood purchased from several Virginia locations of one national retailer, and new cases are likely to emerge. (See news article at: http://www.newsadvance.com/news/local/boxwood-blight-hits-lynchburg/article_a2860e97-438c-523a-9c63-202902eaf42b.html).

We strongly recommend that growers purchase boxwood from a nursery or retail outlet that has purchased boxwood exclusively from a boxwood producer in the Boxwood Blight Cleanliness Program (http://www.vdacs.virginia.gov/plant-industry-services-boxwood-blight.shtml). These producers follow stringent practices to avoid the introduction of this disease to their nurseries and are subject to followup inspections by the Virginia Department of Agriculture and Consumer Services.

Black streaking on green stems of boxwood plant with boxwood blight.

Black streaking on green stems of boxwood plant with boxwood blight. (Photo by A. Bordas)

Symptoms of boxwood blight include leaf spots, black streaking on stems and severe defoliation. Other diseases of boxwood, such as Volutella blight and root diseases, can be confused with boxwood blight; therefore, laboratory confirmation is necessary. Learn to recognize symptoms of boxwood blight by viewing the image gallery on the Virginia Boxwood Blight Task Force web site (http://www.ext.vt.edu/topics/agriculture/commercial-horticulture/boxwood-blight/). Information on best management practices, resistant boxwood cultivars, and sanitizers for cleaning tools is also available on the web site.

In all the cases of boxwood blight diagnosed by the VT Plant Disease Clinic in home landscapes, the disease was introduced on infected boxwood plants. The fungus has sticky spores and is not adapted for movement on air currents; however, spores may stick to and be transported by spray hoses, tools, clothing, shoes, and vehicles. The fungus can also be transported in soil and likely by animals moving through infected plants, e.g. deer, dogs. Infected boxwood may also be present in holiday greenery.

If you suspect boxwood blight, collect symptomatic branch samples with at least a few green leaves still attached. Double bag the samples in sealable bags and take them to your local Virginia Cooperative Extension office (http://www.ext.vt.edu/offices/index.html). Samples will be forwarded to the Virginia Tech Plant Clinic for diagnosis.

Boxwood Blight on Boxwood Holiday Greenery

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Boxwood blight has been present in Virginia since 2011 and has since spread from its original location in Carroll County to a number of other counties around the state by movement of infected plants. Because much of Virginia’s greenery production industry is located in areas where boxwood blight is known to occur, the potential for spread of the disease on boxwood greenery also exists. Last year we notified agents regarding the potential for spread of the disease via holiday boxwood greenery. Now that potential has become a reality in North Carolina. The North Carolina Department of Agriculture and Consumer Services recently discovered boxwood blight in holiday boxwood greenery sold at several retail locations in North Carolina. Although the fungus that causes boxwood blight is not active at cold temperatures, it produces structures that can survive on plant debris over the winter. The fungus could potentially infect nearby susceptible plants in the landscape when favorable weather conditions return. Therefore, it is very important that boxwood greenery be properly disposed after the holidays by double-bagging and removing to the landfill. Do not compost boxwood greenery and do not leave it in cull piles in the landscape. Inspect boxwood greenery carefully for symptoms of boxwood blight before introducing it to a site containing susceptible boxwood plants and discard symptomatic greenery as described above. Symptoms of boxwood blight include brown leaf spots with dark border, black streaks on green stems, and leaf drop. Be aware, however, that even asymptomatic greenery could potentially harbor the pathogen. If clientele have highly valued boxwood in their landscape, they may want to avoid introducing boxwood greenery altogether.

For more information on the North Carolina situation, refer to the NCSU Plant Disease and Insect Clinic blog at: http://ncsupdicblog.blogspot.com/2014/12/pest-alert-boxwood-blight-on-holiday.html.

For more information on boxwood blight in general, including Best Management Practices for the greenery industry, landscapers, home growers, and retail and wholesale nurseries, visit the Virginia Boxwood Blight Task Force web site at:http://www.ext.vt.edu/topics/agriculture/commercial-horticulture/boxwood-blight/index.html.

Please make sure that property managers of historic sites in your area are informed about this update.

Leaf spots on boxwood caused by the boxwood blight pathogen (photo by A. Bordas)

Leaf spots on boxwood caused by the boxwood blight pathogen (photo by A. Bordas)

Black streaking on boxwood stems caused by the boxwood blight (photo by A. Bordas)

Black streaking on boxwood stems caused by the boxwood blight pathogen (photo by A. Bordas)