Information provided by UMass Extension, Nursery, and Urban Forestry.
In December 2011, the UMass Extension Plant Diagnostic Lab working with samples collected by MA Dept. of Agricultural Resources (MDAR) inspectors positively identified boxwood blight (Cylindrocladium pseudonaviculatum) in Massachusetts. Beginning in early December, MDAR inspectors performed trace forward surveys of nurseries and garden centers identified by USDA APHIS PPQ as having received boxwood plants from nurseries in CT known to have some boxwood blight infected plants.
In the mid-1990’s, plant pathologists in the United Kingdom first identified the fungal disease. By 2002, boxwood blight was present in New Zealand. How the fungus arrived in the United States is unclear, but within the last year, it has turned up in Virginia, North Carolina, and Connecticut landscapes, garden centers, and nurseries.
The most susceptible species appear to be English (Buxus sempervirens ‘Suffruticosa’) and American or common boxwood (B. sempervirens), although many species of boxwood are susceptible to infection. Asymptomatic but infected plants of resistant varieties can introduce this pathogen to uninfected areas. The fungus colonizes all aboveground portions of the plant. Initial symptoms appear as dark or light brown circular leaf spots. Infected leaves then turn brown-tan, which is rapidly followed by defoliation. In addition, black lesions often develop on twigs and stems. Plants are not killed by this disease, but become so defoliated as to be aesthetically unacceptable. Infected plants introduced into older, well-established plantings will rapidly spread the disease to healthy plants.
This disease is spread primarily by water (rain splash, irrigation, runoff, etc.) and by the movement of plant material in the trade. The best management strategy at this point, before more is known about this pathogen, is to not introduce any boxwood from unverified sources, either into the nursery or landscape. For more information about this emerging issue, go to UMass Extension Landscape, Nursery, and Urban Forestry website at http://www.umassgreeninfo.org for a fact sheet with a detailed description of boxwood blight and its management.