Boxwood Blight should be confirmed before any treatment is attempted; most disease we encounter is caused by other fungi, not this specific blight. (For example, Volutella Blight is often misdiagnosed as Boxwood Blight, but they do not share the same symptoms.) Have you seen the particular symptoms associated with that disease, or has a landscaping company sent samples for testing of suspicious symptoms?

Over-the-counter products containing the active ingredients propiconazole or chlorothalonil (either one, not combined) will likely work to suppress infection before it occurs, but cannot cure existing infection (no treatment would). Multiple protective sprays would likely be needed throughout much of the growing season, but refer to product label directions for use. Given the fact that fungicides can fail to work, cannot cure, and can be expensive to use yearly for the life of the plant, we generally do not recommend their use if plant replacement is a possibility. While there are more highly blight-resistant boxwood cultivars on the market these days, none are likely to be perfectly immune, and if they succeed in avoiding this fungus, they can still contract other issues typical for boxwoods (like mites, leafminers, or Volutella).

Miri