Question
I have four acuba that were planted last fall.  They went through the winter not problem. Now, however, I have leaves turning yellow from the bottom up and dropping off.  Any ideas of what is up?

Answer
Depending on where you are , this could be due to the winter.
Thus, leaves falling off would be just a sign of the plant trying to rejuvenate its growth.

On the other hand, it could also mean some fungal infestation.

They would usually appear after an infestation by scales.

Fungal infestations such as caused by Phyllostica Aucubae could be detected by brown or black spots that would develop mostly around the margins of the leaves.
In serious cases, much defoliation will occur.
See what kind of fungicide is available to the public in your state.
If you could send me pictures a could give you a better answer.

Keep in touch!

Carlo