Copper Sulfate is quite effective against anthracnose, but only slightly effective against Powdery Mildew. If you keep your spray mix constantly shaken, you can spray with elemental Sulfur--- do not mix elemental Sulfur with Copper Sulfate, or with most other Copper molecules, as Copper ions become very toxic to plants in highly acidic tank mixes.
Spread more than half of that fertilizer out on the grass outside the ring. Make sure you use fertilizer containing micronutrients, including Zinc. Make sure your soil has plenty of Calcium, or add Calcium Sulfate--- it provides also protection against fertilizer-imbalance burns and excess salt build-ups.
Occasionally provide a deep watering--- not just grass root-depth watering--- perhaps just once a month, since the tree already looks reasonably well.