Boxwood blight

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.

ALERT: Boxwood Blight Found in SC

Boxwood blight, Cylindrocladium pseudonaviculatum, was discovered by landscapers in the Florence, SC area where it had likely been present for several years. Boxwood blight is not a regulated pest of concern in South Carolina, however, it is extremely detrimental to many boxwood cultivars and almost always requires plant removal and extensive environs clean-up.

Tracebacks have revealed that the disease most likely hitchhiked in on infested nursery stock from out-of-state nurseries. Boxwood blight has not been found in production nurseries in South Carolina.

Be on the lookout for the newly arriving disease and use good sanitation practices so as to reduce the spread of the disease once it has arrived in a given area. The most likely means of spread is mechanical by landscapers. Send highly suspect samples to the Plant and Pest Diagnostic Clinic for further analysis.

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.

A collage of boxwood blight symptoms

Photo collage courtesy of: Nicole Ward, UK Cooperative Extension

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 Extension office.

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