Boxwood blight is caused by the pathogen Calonectria pseudonavicu-latum, and will also affect other shade-loving plants like sweet box and pachysandra. The photos below show the progression of symptoms: First you’ll notice circular lesions with dark brown edges on the leaves and black streaking on the stems. As the disease spreads, foliage turns straw-colored, then falls off. Sometimes this can be confused with volutella blight or winter burn; a tissue test at a plant disease diagnostic clinic can confirm boxwood blight.
How does boxwood blight spread?
Boxwood blight is spread by contact with infected plants from nurseries, tools, clothing and even greens in holiday decorations, such as a wreath or center-piece. Spores can persist in the soil for up to 5 years, so even a new boxwood planted where an infected plant was removed can become diseased. There is no cure, so you will need to either begin treatment if you have too many plants to lose or remove the entire plant.