There are several different fungi that can cause spots on leaves like this,   Your best option is to take a sample of several leaves to your county extension office so they can send it to NDSU to see which one is causing the damage. Also if you live in a town with a city forester they may be able to tell what it is by actually looking at the tree. In the mean time be sure to give your trees extra water.   A good soaking once a week should be done on trees this young until this drought breaks. 

Contact Esther McGinnis at the extension office on campus.   231-7971 or 231-7406  they should be able to direct you.   Usually you take them to your local extension office and they send them in for you.