Insect and Spider Identification: My poor Hydrangea.....HELP!, 1 by kastrol

kastrol wrote:
This is on my Hydrangea. It is like little cotton dots. It starts out with just a few on the undersides (mostly) of the leaves, then they just multiply into groups. When the leaf gets alot on them it starts to turn yellow and then falls off. The Hydrangea still flowers.....it just looks unsightly with the white dots and I am sure it can't be healthy for it if the leaves are turning yellow and falling off. I would like to know what it is and also what I could do to help it.
I would appreciate any help or information, Please!!