Hello Edelle, 

Thanks for reaching out! I am sorry to read about your cherry tree. It is my understanding that there have not been any reported cases of Little Cherry Disease in Minnesota -- this disease has affected cherry trees in WA and OR, for the most part. 

X-Disease, on the other hand, has been reported in Minnesota in cherry trees. This disease is caused by a bacterium that is carried between trees by insects known as "leaf hoppers". Symptoms of X-Disease include small fruit and poor color development. This link shares more about the disease: https://treefruit.wsu.edu/crop-protection/disease-management/western-x/

This bacterium can be identified through laboratory testing. The University of Minnesota has a plant disease clinic that has reported doing this type of testing in the past. If you wish to pursue the plant testing option, it is recommended to contact them first and confirm whether they still do this testing. More information can be found here: https://pdc.umn.edu/

You may also consider hiring a certified arborist to conduct an onsite inspection of your cherry tree. I am happy to read that the rest of your tree looks healthy, so perhaps the arborist will have ideas for encouraging a better cherry harvest after they see the tree in person. They will be able to evaluate the tree for disease, in addition to any environmental issues. Here is a helpful link: https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional

I hope this helps!