Peach leaf curl, a common fungus disease of peaches. too late to spray this year. This year, collect and discard all affected leaves as promptly as possible.

Thank you Jean - what spray do I need for next season?

Contact your count's Extension Service office as they will know when and what is appropriate for your region.

Locate that office with this interactive map:

http://npic.orst.edu/pest/countyext.htm

If that is peach leaf curl (and I don't believe it is), it is an extremely mild case and seems to be isolated to a single leaf. Generally, leaf curl will affect a significant portion of the new growth and produce contorted, swollen and fleshy, almost blistered leaves, frequently with reddish discoloration.

Unless there is a lot more going on with this tree that we do not see, that looks a lot more like mechanical damage to the leaf than anything else.