Originally Posted by agrostis
For a definitive answer send a sample to the plant pathologist at UGA. For a in-state resident it should only be 5-10 dollars.
Yep, that's going to get your answer.
Now, we've been experiencing the same type of conditions on most boxwood's locally.
Only thing I can find is it's just generally evergreen decline especially if the soil stays wet and doesn't dry out. The term "Bronzing" of boxwoods has been thrown around by the Illinois extension offices.
This winter I expected the boxwoods showing these symptoms to stay greener and healthier this winter but it's been exactly the opposite. The bronzing is still present in lots of landscapes.
As for the residue. It's either powdery mildew like suggested before, or it's hard water stains on the leaf tissue from watering.