Hello,

There are many things that may have caused the browning of your boxwood leaves. The damage may be caused by insect pests, diseases or environmental factors. Insect pests could be leaf miner, psyllid and/or boxwood mite. See the attached to read more about these insect pests.

https://www.canr.msu.edu/news/boxwood_insect_pests

Many diseases may affect boxwood including boxwood blight.

https://extension.psu.edu/boxwood-diseases

Environmental factors that may cause the leaves to turn brown include winter desiccation and cold damage. If the shrubs are close to a sidewalk where salt is spread in the winter, salt damage can occur.

In addition, the USDA has confirmed the presence of the box tree moth in continental US and is working to contain and eradicate this invasive species. Read more here: https://www.canr.msu.edu/news/boxwood_insect_pests

And here: https://www.canr.msu.edu/news/what-growers-and-landscapers-need-to-know-about-box-tree-moth

Because these problems show similar symptoms, it is difficult to diagnose and decide on a method to deal with it from a photograph. And some problems, such as boxwood blight, can only be correctly identified with a laboratory analysis. The Plant and Pest Diagnostic Lab at MSU Extension will be able to help you solve the problem. Go to https://www.canr.msu.edu/pestid/ to learn how to submit a sample. Because you purchased your boxwood plants in the past year and a half, I strongly urge you to contact the Diagnostic lab for identification of the problem.

Thank you for contacting Ask Extension.