Question
I have 2 willow trees in opposite sides of my yard and both of them are deeply infected.  It appears to be a raised bump on the one side of the leaves and on the other side it looks shrivelled up and sunk in slightly.  What is this and what do I use to be rid of it?  Unfortunately I do not know the age or type of willow tree because I got it when I was very young.  I do have pictures of the leaves if it would help in your search.  I have looked all over the internet at willow tree fungi and disease, but couldn't find anything that's my situation.  If you could help me that would be great!  
Thank you for your time,
June


Answer
I think you have one of the willow gall insects that will from time to time attack wiilow. These generally will not kill the tree BUT will make to look quite sick. Generally chemical controls are not needed but you can cut down the next years population by raking up and distroying the fallen leaves. Insects usually run in cycles and the population will buildup and the insects natural enimies will also build up and the population will decrease. Here is a web site link that describes gall insect on willows.
http://www.treehelp.com/trees/willow/willow-iandd-galls.asp