These peaches were found pretty widespread in an 8-year-old Cary Mac orchard in GA in 2010.
This Red Suture disease was caused by an accidental 2,4-D herbicide application, which reddened the suture area early and produces a bulge at the suture. Damage was also noticeable on the non-suture part of the fruit and on leaves. Similar symptoms at the suture end can be induced by a leaf hopper-vectored phytoplasma, but infected trees might be more likely to be found near the boundary/hedge row.
In 2011 the same symptoms were found on 5% of the fruit in two blocks of Contenders in Anderson county SC. Trees from the two blocks were of different age and from different nurseries. Grower applied 2,4-D during dormancy in February. We believe that the volatile 2,4-D drifted to the buds and precipitated in high enough concentrations to cause this damage. This herbicide has growth regulator effects.