Thank you for writing.
I need a close up of the out side a twig where the leaves are dying, not dead.  Then, I would like you to cut that branch where it is about 1/2 inch in diameter and send me two pics, one the cross-section where you cut the branch and the other of the bark near the cut.
https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/crabapple/branchdieback.html
I would guess botyris but I need more information.

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Thank you for writing back.
Has this tree been exposed to aerosolized herbicides (weed killer) from your yard or from a neighbor?
https://www.ndsu.edu/agriculture/extension/extension-topics/gardening-and-horticulture/trees-and-shrubs/apple-trees/apple-tree-leaf

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Thank you for writing back.
Here is the list I am working from now. 
The cut cross branch would seem to rule out Botryosphaeria canker.
That pushes me to fire blight or scab,  https://extension.psu.edu/crabapple-diseases

I prefer scab, it is most common and the leave descripion matches yours. https://extension.umn.edu/plant-diseases/apple-scab#fungicides-to-protect-ornamental-crabapples-from-apple-scab-3652960

You have a couple options.
You could send a speciment toe the Univsity Plan disease department. https://pdc.umn.edu/submit-sample
You could ask and arborist to comel . https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional

Given the siize of the tree I do not think you could apply anti fungals yourself.

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Dear Steve, here's the response to your question:

Thank you for writing back.
Here is the list I am working from now. 
The cut cross branch would seem to rule out Botryosphaeria canker.
That pushes me to fire blight or scab,  https://extension.psu.edu/crabapple-diseases

I prefer scab, it is most common and the leave descripion matches yours. https://extension.umn.edu/plant-diseases/apple-scab#fungicides-to-protect-ornamental-crabapples-from-apple-scab-3652960

You have a couple options.
You could send a speciment toe the Univsity Plan disease department. https://pdc.umn.edu/submit-sample
You could ask and arborist to comel . https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional

Given the siize of the tree I do not think you could apply anti fungals yourself.

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Steve Miles  Master Gardener, Hennepin County MN (Not an AI Bot)

I am always happy to receive follow-up questions if I do not fully address your question.
Sterilizing pruning tools prevents disease. https://extension.umn.edu/planting-and-growing-guides/clean-and-disinfect-gardening-tools

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Fertilizing the tree in the fall is not a recommended procedure. Stimulating growth when a tree should be going dormant may produce new growth that is tender and easily killed by the first frost.  
These trees generally don’t need fertilizer.  Fertilizing the tree now giving it time to harden new growth would be okay. But the best time is to wait until spring. Overfertilizing can reduce blossoming and fruit production.

I can’t comment on the injection without knowing what they are recommending. But it not a recommended procedure unless they found something other than apple scab.

The most important thing you can do to prevent return of apple scab is to clean up leaf/branch/fruit litter from under the tree in fall.