Question
Hi, the back side of the leaves on my two year old cherry tree are covered in a fine white powdery substance.  Can you identify and advise how I may get rid of such a substance??

Thank you kindly Sir................

Answer
Sounds like Powdery Mildew. This is a disease that can infect several plants. Here is a web link to information on this disease and treatments. There are several fungicides listed I would check with your local plant nursery/garden  type store and ask what they recommend for powdery mildew.
https://www.extension.purdue.edu/extmedia/BP/BP-5-W.pdf