Boxwood Blight is a disease to boxwood that is caused by the fungus Calonectria pseudonavicultata. The symptoms of this disease is leaf spot, black streaks along the twigs, defoliation, dieback on older plants and death of container and young boxwood. Pachysandra and Sarcoccoca are also hosts. Use care in selecting new plants. Keep an eye out for the symptoms, remove any infected parts of the plants, keep debris/leaves from around the boxwood and disinfect pruners with bleach or alcohol. Just keep vigilant.
University of Delaware Cooperative Extension – Boxwood Blight