Greetings Dr. Wassermann, I am glad you were able to upload this photo as it definitely provided some clues for diagnosis.  My first impression is a foliage disease known as tar-spot but that is not something I have been familiar with on tulip tree.  Most of the information from university diagnosticians note different leaf spots that are attributed to environmental stress- yet this one has clear signs of being fungal.  Then I discovered one reference from University of CA that specifically noted that tulip trees can indeed get tar spot.  That said- this is a cosmetic disease, usually affecting maple trees.  Normally we start to see it later in the summer (August) but we did have some early spring weather in Michigan. Here is an article written by one of my colleagues that you may find interesting. https://www.canr.msu.edu/news/why_do_my_maple_leaves_have_spots