The interior of a group of previously healthy mature (60 yrs) English boxwoods appears to be dying. It does not look like blight - the leaves on some of the interior stems simply start to take on a smoky grey color that progresses to death - no yellowing, no spots, no obvious leaf pathogens, just smoky grey progression. It is barely possible that it is not a disease at all, just interior leaf dying similar to what occurs on conifers; however, I have never seen this before on these or any other boxwoods.
Boxwood are subject to many disease and insect problems. The most serious is boxwood blight. For information on boxwood blight go to the following link on our website: http://extension.umd.edu/hgic/invasives/boxwood-blight
For information on other boxwood diseases please see the following information from our website, http://extension.umd.edu/hgic/boxwood-culture-and-diseases-including-boxwood-blight
Have you or your neighbors planted any new boxwood recently? As this is how boxwood blight is introduced into landscapes. But, there are specific symptoms that differentiate this disease from other boxwood diseases. Look for defoliation, stem cankers, etc.
Do you have landscape companies taking care of your property? Has something changed in the area? Drainage?
Also, look for voles (a type of meadow mouse that feeds on the roots of trees and shrubs). Look for silver dollar sized holes around the base of the shrubs or gnawing on the bark of stems, http://extension.umd.edu/hgic/voles
Our boxwood publication may also be helpful for more:
You can get back to us with more information regarding the above.
Thank you for your response. None of the specific features of blight or other changes you mention has occurred. Two other experts on boxwoods (Hillwood Estate in DC and Saunders in Virginia) have both said that the condition is not blight, and both (like you) have come up blank on what is causing the problem. I guess the next step would be to cut an affected stem and bring it to you for inspection. How do you suggest I proceed?
You did not mention if there are landscape companies working on your property.
Check again around the base of the stems and look for gnawing or chewing by voles. Let us know.
You can send us samples of the shrub in question. Send us samples of branches with green foliage going from good to bad. You can include some dead branches. Wrap the branches in newspaper or paper, no plastic.
Mail to HGIC, ATTN: David Clement, 12005 Homewood Road, Ellicott City, MD 21042.
Mail after Thanksgiving so the sample does not sit.