Your poor mandarin tree looks like it is in dire need of water. How frequently are you watering it? I would make sure you are watering sufficiently, and apply fertilizer again, then water it in, well. Make sure you apply the fertilizer to the drip line, and not just at the trunk. The feeder roots are at the drip line. And, you might want to consider mulching your tree to help conserve moisture. You don't mention where you are in the country?? If you're in a warm (or hot), dry area, you're going to want to deep water your citrus tree at least once a week, or more often if you're somewhere like AZ, inland S. California or Texas. Also, if you have very well draining soil (your soil looks to be a little sandy?)

Patty S.