Good Morning Susan, 

Thank you for contacting the U of M Extension Service. 

With the cool and wet spring we've experienced, there is lots of fungi issues in the garden. 

Here is a link from the U of M Extension Yard and Garden website about growing stone fruit: 

https://extension.umn.edu/fruit/growing-stone-fruits-home-garden#diseases-2836762

If you scroll down, it discusses possible diseases of your tree. If you follow the links, there is a link to cherry leaf spot: https://extension.umn.edu/plant-diseases/cherry-leaf-spot

From your description, I immediately thought about powdery mildew: https://extension.umn.edu/plant-diseases/powdery-mildew-trees-and-shrubs#trees-and-shrubs-commonly-affected-by-powdery-mildew-1584110

Here is a link to the plant disease clinic if you deicde to submit a sample: https://pdc.umn.edu/

Good Luck!