While I can’t give you a diagnosis from a photo, it looks like your Redbud may have Cercospora - a fungal disease. There is no need to spray it with anything. 

You don’t say if this is a Minnesota Strain, but those are actually bread in Minnesota and survive the best here. 

We have had a 3 year drought and all of our trees are stressed. Stressed trees are more susceptible to disease. Be sure to keep your tree well watered through the summer and until the ground freezes in the fall. Trim out any dead branches and thin out the canopy if it is too thick. You want to have good air circulation.

https://trees.umn.edu/northern-strain-redbud-cercis-canadensis-northern-strain