How to control English boxwood blight and save the plants
Sussex County Delaware
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,