January 2014 Plant Disease Update

boxwood grouping with blight symptoms
Defoliation of susceptible boxwood due to boxwood blight. (Photo courtesy of A. Bordas)

Boxwood blight, a fungal disease that was first found in the United States in 2011, has spread from its original location in one nursery in southwestern Virginia to several landscapes and garden centers in other parts of the state as of fall 2013. Symptomatic boxwood plants were first found in the Richmond area in October and in Fairfax County shortly thereafter. Wet fall weather favored the disease. In the early stages of disease, plants develop circular leaf spots with dark borders and lighter brown centers and black streaking appears on stems. Roots are not affected. Leaves ultimately turn brown and drop. Sudden, severe defoliation is a strong indicator of box blight.    Although boxwoods are also prone to root diseases, leaves that turn brown due to root disease typically remain on the plant. English and American boxwood, which are widely planted in Virginia, are very susceptible to the disease.

 

boxwood limb with leaf spotting
Leaf spots due to boxwood blight.

Some boxwood cultivars appear to have tolerance to box blight and may not show severe symptoms. When infected, tolerant plants are introduced to an area with existing boxwoods, the disease can spread to nearby susceptible plants.  This is the likely means by which the disease was introduced to several landscape sites in Virginia. To reduce the chances of introducing this disease to a landscape, it is advisable to purchase boxwood plants from producers participating in the Boxwood Blight Cleanliness Program. These producers adhere to strict practices that minimize the chance of introduction of the disease, and their nurseries are inspected by the Virginia Department of Agriculture and Consumer Services for presence of the disease. Because the disease can also occur on boxwood greenery, it is important to dispose of boxwood greenery after the holidays by bagging and discarding in the landfill. Greenery should not be composted or left in cull piles.