bugs on hydrangea

these are all on my hydrangea leaves and also the stems, the plant has flowers on it, but not as  large as they normally are,  The infestation is all over the leaves on the underneath and almost look as though they are made of cotton.  I have no idea as to what they are and which is the best way of treating them, so rather than wait for it to be desimated, i've cut all the infected stems down and gathered the soil up where the eggs/bugs have fallen, bagged themup and taken them to the tip.  has anyone ever had any dealing with anything like this...thanks