Boxwood Blight (also known as Box Blight) is a devastating fungus disease that affects boxwoods (Buxus spp.), although some species and cultivars are more susceptible than others. English boxwood (Buxus sempervirens ‘Suffruticosa’) and American or common boxwood (B. sempervirens) are highly susceptible to boxwood blight pathogen. There are no known resistant cultivars; however, tests at North Carolina State University have found B. sinica var. insularis 'Nana' and B. microphylla var. japonica 'Green Beauty' to be tolerant.
The boxwood blight causal organism, the fungus Cylindrocladium pseudonaviculatum, only attacks the above-ground portions of boxwoods and not the roots. Infected leaves develop light or dark brown spots or lesions. These spots can coalesce and entire leaves turn brown or straw-colored. Eventually the “blighted” leaves drop. Infections on the stems result in dark brown to black lesions or cankers. When these cankers coalesce, the stems become girdled and die. The pathogen survives in diseased tissues—including leaves that have fallen to the ground and cankers on stems that remain attached to the plant. The fungus spreads by splashing water caused by irrigation or rainfall. Pruning also can contribute to movement of the pathogen. Long distance dispersal is facilitated by the transport of infected nursery stock and plant debris. Wind apparently does not aid in dispersal of the spores over long distances.
Boxwood blight can be confused with other boxwood diseases and disorders, such as Volutella blight, Macrophoma leaf spot, boxwood decline, and winter injury or sunscald. If you observe symptoms on your boxwoods, it is important to have the disease accurately identified by a specialist. For more information, contact your local County Extenstion office.
Photo collage courtesy of: Nicole Ward, UK Cooperative Extension