My mandarin tree was doing really well a year ago. This year the crop was still good but the fruit was much smaller. Recently it started getting black fungus over it and it looks like it has leaf mites. After discussions at the local nursery, I was told to fertilize and prune back to open up the canopy to let more air through. Unfortunately all this seems to have made the problem much worse. The leaves have curled, turned yellow and it looks as though the whole plant might die. Does anyone have suggestions on what I can do?

Thanks for your help. Allison

(in Australia, early Spring)