Thanks for your question.

Crab apple trees in Minnesota are susceptible to several diseases, many of which are also common in other types of apple trees. Sometimes a correct diagnosis can be made with just pictures. More often, a professional, licensed arborist should make an onsite examination and assessment. See:

https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional

Here are some common crab apple diseases and their symptoms. Use these as a guide in deciding exactly might be affecting your tree:

1). Apple Scab: This is caused by a fungus (Venturia inaequalis) and leads to olive-green to black spots on leaves and fruit. Infected leaves may yellow and drop prematurely, and fruit may be deformed or cracked.

2). Fire Blight: This is a bacterial (Erwinia amylovora) disease that causes wilting, blackening, and death of blossoms, leaves, and branches.

3). Cedar-Apple Rust: This is a fungal (Gymnosporangium juniperi-virginianae) disease producing yellow-orange spots on leaves, which can develop into lesions with black dots. In severe cases, leaves may drop early.

4). Black Rot: This is a fungal (Botryosphaeria obtuse) disease characterized by sunken, dead areas on branches, sometimes exuding dark sap.

See:

https://www.lawnstarter.com/blog/tree-care/apple-tree-diseases-how-to-treat-them/

In my opinion, your pictures indicate the possible existence of Fire Blight. As previously mentioned, you need to enlist the assessment of a professional arborist for a compete verification of this. As an alternative to an arborist., consider submitting plant samples to a diagnostic disease laboratory for an analysis. This would be a definitive way of getting to the bottom of things. Both Wisconsin and Minnesota have excellent labs to do this. Before submitting anything to either of them, call first as to what type of samples should be submitted. Both have a nominal charge for their analysis. See:

https://pdc.umn.edu/

https://pddc.wisc.edu/clinic-overview/

Good luck. Thanks for using our forum.