Gnat Bytes:

Extension News for South East Georgia

Boxwood Blight in Georgia

Boxwood blight photo

Boxwood blight symptoms clockwise from upper left: Tan to gray leaf lesions with a darker purplish border on an English Boxwood. Circular, tan spots with a brown border on upper leaves, Tan blighted leaves and bare stems on an infected plant, blackening of stems and browning foliage, and black stem lesions on bare branch tips. Images by Jean Williams-Woodward

By  Jean Williams-Woodward, UGA Plant Pathologist

Boxwood Blight, caused by the fungus, Calonectria pseudonaviculatum (syn. Cylindrocladium pseudonaviculatum and Cylindrocladium buxicola) has been confirmed in multiple commercial and residential landscapes in GA. The disease could be found throughout the state; however, most of the confirmed detections have been within metro-Atlanta and the surrounding counties where boxwoods are common in formal gardens. Boxwood blight also has been detected on plants brought into GA for resale. Often the source of the introductions is unknown. In some cases new boxwood plants were recently planted.In others, it may be from pruning or other garden maintenance operations. The spores of the pathogen are very sticky and they can stick to worker’s tools, clothing, or even animal fur (cats, dogs, rabbits, etc.) that may move through the garden. Once introduced, the disease can be devastating to boxwood in landscapes and nurseries.  

 Hosts:Dwarf English boxwood (Buxus sempervirens ‘Suffruticosa’) is highly susceptible and develops severe symptoms and rapid leaf drop. American or common boxwood (B. sempervirens) cultivars are also very susceptible. Cultivars of Littleleaf (Japanese) and Korean boxwood (B. microphylla and B. sinica, respectively) appear less susceptible because they don’t show severe symptoms and leaf drop, but they are still susceptible. None of the commercial boxwood cultivars are immune to this disease. In fact, lesser susceptible (e.g. tolerant) cultivars may act as a ‘Trojan Horse’ introducing the disease into landscapes containing more susceptible cultivars. The value of lesser susceptible cultivars is in the establishment of new boxwood hedges. If planting a new area, use a more tolerant cultivar to lessen your disease pressure in subsequent years. The disease also affects other plants within the Buxaceae family, including Pachysandra terminalis (ground spurge) and Sarcococca sp. (sweet box).  

 History:Boxwood blight was first identified in the USA in the fall of 2011 in NC and CT. Since then, it has been identified within nurseries and/or landscapes in numerous states (AL, CT, DE, FL, GA, KS, KY, MA, MD, MO, NC, NJ, NY, OH, OR, PA, RI, TN, VA, WV) and several Canadian provinces. The disease is spreading to new states each year (FL and WV were added to the list in 2015). Spread is most likely through the movement of infected plants. The disease has been known for over decade in the UK and Europe.  

Symptoms:Initial symptoms of boxwood blight include circular, tan leaf spots with a dark purple or brown border. Leaf spots may or may not have yellow to reddish halos surrounding the spot. Black stem lesions or blackening of the stems is often seen. This can be confused with black lesions due to Colletotrichum stem canker, a relatively new disease also affecting boxwood stems. Boxwood blight

Infected leaves become tan and readily drop from the plant leaving bare stems. Rapid defoliation is a characteristic symptom of boxwood blight that separates it from other boxwood diseases. Sections or whole plants turn tan and eventually die. The disease can resemble Volutella blight, except that with Volutella blight, as well as with symptoms of root stress or Phytophthora root disease, the leaves often remain attached to the stems. Box blight can move quickly through infected plants, gardens, and nurseries under favorable environmental conditions.