The first question to answer is whether you indeed have boxwood blight caused by the fungus Calonectria. There are a number of reasons that boxwoods may show dieback, and environmental stress is the most common. There are a couple of fungal diseases that boxwoods are susceptible to.
Boxwood blight is a fungal disease that was first found in the U.S. in 2011, and was found in Delaware in 2012, but those plants were eradicated. So, I would suggest that we try to confirm what the boxwoods are suffering from first and then work on management. You are welcome to take a sample to the Carvel Center on Highway 9 in Georgetown, or to send a sample directly to the Clinic. Please see the website for the sample form and instructions: http://extension.udel.edu/ag/plant-diseases/ud-plant-diagnostic-clinic/
We also have a fact sheet on boxwood blight that may be found at: http://extension.udel.edu/factsheets/boxwood-blight-caused-by-the-fungus-cylindrocladium-pseudonavic...
Thank you for contacting Delaware Cooperative Extension,