As peaches begin to ripen they are prone to have insect and disease problems. In particular, june beetles and brown rot can destroy most of the fruit on the tree. June beetles are attracted to ripening fruit and will congregate in large enough numbers to completely consume the fruit. The picture shows not only june beetles but wasps and hornets feeding on ripe fruit.
The feeding injuries are prime sites for brown rot infections. Brown rot develops quickly on the fruit and can also spread quickly to other fruit on the tree. The peach shown in the bottom picture has brown rot on over 50% of its surface and is beyond salvaging.
In order to protect fruit from insects and diseases, peaches should be sprayed on a weekly basis beginning 4 weeks before anticipated harvest. Some stores carry a product that already has the insecticide and fungicide mixed together. Make sure you get thorough coverage to prevent brown rot from becoming established.