Hello Al,

There are many things that may have caused the browning of boxwood leaves including insect damage, diseases and environmental factors.

Insect pests could be leaf miner, psyllid, a small jumping insect 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

It looks from the picture that your boxwood is infested by leaf miner which, you will note, is very difficult to treat. Read more here about prevention and control of boxwood insects. https://hgic.clemson.edu/factsheet/boxwood-diseases-insect-pests/

However, because many 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.

Thank you for contacting Ask Extension.