It appears that your Praire Fire ornamental crabapple tree may be suffering from chlorosis since this variety of crabapple is resistant to scab and from your photos does not appear to have fire blight, rust, or powdery mildew.

According to the Colorado State University Extension (http://extension.colostate.edu/topic-areas/yard-garden/flowering-crabapple-trees-7-424/), chlorosis can occur in these trees.
"Chlorosis is not a true disease but rather a disorder. Usually, newest growth shows leaf yellowing with veins remaining green. This lack of chlorophyll may be caused by alkaline or compacted soils, excessive watering, or excessive fertilization. Some crabapple varieties are more susceptible than others."

Below is a link to a website with information on how to care for Prairie Fire crabapple trees that may be useful to you.

http://homeguides.sfgate.com/care-prairie-fire-crabapple-tree-49369.html

I hope this information has been helpful to you.