About a week or so ago my boxwood suddenly turned yellow. I am trying to figure out how to save it. It grew from a twig off a main bush many years ago and it has been thriving until just this short period ago. If you have ideas of what it could be and what I can do I would really appreciate it . I am uploading a picture
It is difficult to see enough detail in this photo but it looks like there might be a crack in the trunk of the plant -- is that true? Is there any evidence of physical injury to the trunk or around the base of the plant? How is the water drainage in this area? Did the plant sit in standing water at any period of time when we had the heavy rains last year? The symptom of overall rapid yellowing suggests a trunk or root problem. If you can provide more information, that will help us diagnose the problem.
No changes in care.
If it is root cause and is a fungus
Is there a way to treat it?
Should I dig it up and rinse off the roots with a fungicide?
Should I avoid planting another one there.
This boxwood is totally dead. As long as there was no standing water there, there's no reason why you can't replant there, but dig up the root ball first.
Boxwood blight disease (your boxwood did NOT die of this) is a big problem in the nursery industry now. You may want to replant with something besides boxwood.