Answer: It sounds like you really love your tree! Pear trees are subject to a common bacterial disease called fire blight. It is so called because branches look like they've been singed--the branches have a characteristic curl and leaves turn black. The following link to the West Virginia University Fruit Research and Education center has excellent photos of symptoms:
Repeated infections can cause serious illness and can kill trees.
If this doesn't look like what your tree is suffering I recommend that you call in a professional certified arborist to diagnose the problem. The NY Botanical Garden can give you references for arborists, I'm sure. Also, I do not recommend further fertilizer for the tree until you have assessed the nutrient content of the soil...too much fertilizer can cause pH and nutrient imbalances in the soil that can actually harm the health of trees. For a soil test, contact your agricultural extension office at ph# 516-454-0900, or ask the arborist to perform one. Best of luck to you!
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