Question
I live in the northeast corner  of Maryland, just south of the Pa state line. I have a paperbark river birch approx. 20' tall I planted last year.

The tree is healthy but in the past week I noticed the leaves becoming more and more wrinkled. On closer examination you can see some white powdery substance on
the underside of the leaves. Is this leaf miners and is the tree in trouble? Please help.

Answer
Sounds like powdery mildew. This is a disease that infects the leaves of a wide number of plants. It can be controlled by the use of fungicides. Here is a web link that discribes powdery mildew and lists the control measures.   http://ohioline.osu.edu/hyg-fact/3000/3047.html