If the dark spots are big and increasing in size, it may be brown rot. If the dark spots are small, it may be some form of bacterial spot. They are fairly harmless, though they will affect the taste. You can apply a copper spray in fall and spring.
As peaches need an entire spray program to thrive, we would suggest you contact your local cooperative extension. Here is a list of offices so that you can find the one nearest you: http://www.almanac.com/content/cooperative-extension-services
If the dark spots are big and increasing in size, it may be brown rot. If the dark spots are small, it may be some form of bacterial spot. They are fairly harmless, though they will affect the taste. You can apply a copper spray in fall and spring.
As peaches need an entire spray program to thrive, we would suggest you contact your local cooperative extension. Here is a list of offices so that you can find the one nearest you: http://www.almanac.com/content/cooperative-extension-services