I think if your county has been having as wet and cool a spring as we have in the metro area it could be apple scab, a common issue for apples and crabapples. This is a fungus that can overwinter on the ground. A wet spring is a perfect condition for the spores which can be carried on the wind to take hold. As the season warms and dries up, the symptoms will decrease. The best thing to do, now is to rake up all the leaves that drop because they can reinfect the tree if you get more rain just when the fruits are starting to form. If it is apple scab, the tree should releaf but I would ensure that it gets enough water for the rest of the season until the ground freezes (usually in December.) Here is more information about apple scab from the U of MN Extension that may help you out: https://extension.umn.edu/plant-diseases/apple-scab-apples-and-crabapples

Another possibility is root damage from that cold snap we had in January when there was barely any snow cover to protect plants' roots.  I'm not sure what the snow conditions were in Murray county so you'll be the judge of this.  If there is barely any snow to blanket the roots and the temps drop deep into even zone 3 levels, plant roots can be damaged.  Sometimes trees will leaf out using the stored energy in their buds but without the support of the roots, the leaves will wither and die.  We have seen this on parts of trees in other areas of Minnesota.  It's possible that it could affect an entire tree but since your trees appear to be well established, I'm not sure this is the case with them.  But I wanted to throw that out for consideration. In this case, I would also ensure that the trees get enough water especially if they releaf so that their roots get a chance to grow.

Good-luck!