Question
My rose bush has white spider-web looking things around the
leaves and white cotton-like masses underneath some leaves.  
What is it?  How can I get rid of it?

Answer
With out seeing your Rose bush I am pretty sure you have powdery mildew.  It will cling to your plant like moss to an oak tree.  

Oils will do nothing, poisons and pesticides will stop the problem but will stunt your plant and alter its growth.

Go to www.atomicgrow.net.  There is a new product on the market not available in stores yet.  I have used this product on many plants and Roses react the best.  First it will clean up your problems and then it will stimulate the plant at the same time.  I usually get reports of a bloom explosion in about 1-2 weeks after applying.

I wont recommend anything else for Roses problems.

Good Luck

James