Peach tree leaf curl is a common fungal disease among these fruit trees. Prevention is the best form of attack against the disease, however. Once your tree has developed leaf curl, it is difficult to save your peach harvest. Unfortunately, fungicide will not kill this disease. Prune off diseased portions of the tree and try to thin out the number of peaches you have on the tree. Also, clean up any debris that may have fallen. In late fall, you can treat with a fixed copper fungicide to try and prevent the re-occurrence of the disease.

While it is often deemed to be less effective than fixed copper products, lime sulphur is an acceptable form of organic control for this disease. Here is an article that you may find helpful as well: https://www.gardeningknowhow.com/edible/fruits/peach/peach-leaf-curl.htm