Pest Alert! Boxwood Blight, A New Disease in North America

Hosts and Symptoms

The fungus causes severe defoliation in container grown Buxus and kills young plants rapidly. Buxus sempervirens, B. microphylla (littleleaf boxwood), B. sinica var. insularis (Korean boxwood), B. colchica and B. microphylla var. japonica (Japanese boxwood) are all hosts. It is not known whether other species of Buxus are hosts. Sarcococca, a member of the boxwood family, is susceptible in inoculation tests. Plant pathologists at The Connecticut Agricutural Experiment Station recently identified Pachysandra terminalis (pachysandra, Japanese spurge) as a new host of C. pseudonaviculatum. Healthy pachysandra plants were inoculated with spores of C. pseudonaviculatum and lesions developed on the leaves ten days after inoculation. Three weeks after inoculation, many of the leaves with lesions yellowed and dropped. Heavy sporulation of the fungus was observed. This raises significant concerns about pachysandra as a potential source of inoculum for infection of boxwood and vice versa. Researchers in the UK believe that Japanese holly (Ilex crenata) is a host. It should be noted that other species of Cylindrocladium have very wide host ranges and that it is very difficult to manage with fungicides.

Boxwoods and their relatives found with blighting and rapid defoliation should be submitted to the Penn State Plant Disease Clinic for diagnosis and/or called to the attention of your Pennsylvania Dept. of Ag. inspector. Box blight can be easily confused with Volutella blight on boxwood (well known to occur in Pennsylvania) as well as other diseases. If box blight is positively identified, plants should be destroyed in order to try to prevent spread to elsewhere in the green industry and the landscape in general.

Visit the Connecticut Agricultural Experiment Station for continued updates on boxwood blight.