Hi- this is brown rot, a common, destructive fungal disease that makes growing stone fruit a challenge for Maryland gardeners and commercial growers. Sanitation and properly timed fungicide sprays help to combat the disease.
The fungus overwinters in twig cankers and in mummified fruit that is left hanging on the tree or has dropped to the ground. So, pick off and dispose of infected fruit (and fruit stems) from the tree and rake up any that has fallen around the tree.
Next year, apply labeled fungicides when the blooms are between 5-10% open, at full bloom, and about 2 weeks prior to harvest. It is best to apply fungicides before a rain event is predicted instead of waiting until after. Additional cover sprays will be necessary if we are experiencing a cool, wet spring and summer. Rotating fungicides helps to reduce the fungus from becoming resistant to the preventative sprays. You can start a spray program this summer to limit infection on clean fruit.
Fungicides available to home gardeners can prevent but not cure infections. Organic fungicides like sulfur and copper can be somewhat effective but may damage new spring growth.
Read more about brown rot: https://extension.umd.edu/hgic/topics/diseases-stone-fruit
Learn about and follow the VA Tech spray recommendations for tre fruits, including peaches: https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/456/456-018/ENTO-289C.pdf