This is a picture of the infected leaves that are falling off my Dwarf Hawaiian Umbrella tree. This started about 2 weeks ago. Every morning there are a couple of leaves that look like the above picture. Often a small branch will fall off if lightly touched, even if the leaves look healthy. The sick leaves are a brownish color. It doesn't look like black spot, but the bonsai has had black spot problems before in the past.
So far we've tried Garden Safe's fungicide (which also is an insecticide and miticide). We've used it twice in two weeks, following the directions on the label. We've also started giving the bonsai Joe Bonsai's fertilizer and vitamins.
We've had this tree since April. It's still growing some new leaves, but it's losing leaves at a faster rate because of this problem. Any suggestions would be greatly appreciated!