Spray with an approved fungicide such as benomyl. The lichen itself is not harmful, but it usually indicate a decline in vigor by the tree. Try to get the tree actively growing again with extra fertilizer and water. If the tree fails to respond, replace it with a new tree. Birds are starting to work on peaches.
Peaches stop ripening once they are picked.
Hence the only answer is to protect the fruit from the birds. Nets are the only sure fire way to prevent this damage. If the owner desires a true cultivar, it is recommended trees from seed be avoided as they will not be true to type. However, if the tree makes a satisfactory rootstock it is ok to be used. What can be used to spray hybrid Bermuda grass in a peach orchard that will get rid of the grass but not hurt the trees.