Question
I planted a couple of small montmorency sour cherry trees in pots to get them to a good size before planting outside.They are about six inches high. When I brought them indoors for the winter(northern ontario)all the leaves died after getting like a very thin covering of white powder on them. The trees lived and grew a few new leaves near the top only to have the same thing happening again. I am at that point now and would like to know if there is anything I can do to save them. I know absolutely nothing about plants or gardening.Thanking you in advance for any help you might be able to give me.

Answer
Sounds like powdery mildew, a fungus that infect many plants. It can be controlled with the use of a fungicide. Here is a web link that will give more information on powdery mildew and the fungicides that will control it. It is one of the diseases that can be easily controlled.
http://ohioline.osu.edu/hyg-fact/3000/3047.html