Thanks for the question. I cannot tell with certainty from the photos. The tree definitely has apple scab a very common fungal disease on crab apple trees. Spreads readily in cool wet weather. Typically, will not kill the tree. Fire blight is a bacterial disease with symptoms of isolated branches, usually high up and new growth, leaves turning brown and wilting as if too close to a campfire. That one branch may fit that diagnosis?? Here is information on both apple scab and fireblight: https://extension.umn.edu/plant-diseases/apple-scab, https://extension.umn.edu/plant-diseases/fire-blight#bark-symptoms-1766162

Paul

Tree Care Advisor volunteer

Bob, It seems to me that I have seen a class offered at the MN Landscape Arboretum but I don't see any currently. Here is a link to their website: https://arb.umn.edu

You might check with them to see if they have any apple class planned.

Paul