I would suggest you bump up the Miracle-Gro a notch to at least a tablespoon to 2 gallons of water. That should perk your brug up. My angel trumpets are just starting to bloom. See a picture of one of my Charles Gramaldi brugs that I posted on my blog link below.

Jon on 8-7-07

Here is a link that might be useful: Mississippi Garden

This is my first year with Brugmansia, but as far as I can tell, it is normal for the bottom or "trunk" leaves to yellow and fall off, especially in containers.
Considering yours is 9 feet tall (dont know if it is in a container), I am not surprised if it is the lower leaves falling off. all the searches I do for images, in google show leafless trunks so that a bushy Brug eventually becomes more tree-like.

You might consider doing a search in the brugmansia forum.