Dear Carol: Given your description, I will make a good guess for you. You may have a systemic disease called "black knot" that has established itself in your trees. There is no treatment for this condition. You should contact your local extenion office for confirmation before taking any corrective measures.
Other possibilities include having winter weather damage the flower buds, limiting the number of cherries you had this season. Another one may be a foliar disease that could be treatable once identified for proper timing and material to be used.
Sincerely, Richard
