Hi, 

It is difficult to say for sure what is causing this between potential borers or a canker disease. You can prune out the smaller twigs and branches but there won’t be much you can do now on any trunks or larger branches. 

You can visit our Stonefruits page for guidance. Under the tab “Plant and Pest Problems” there are links for further information on Cytospora canker and peach tree borer. You can explore those for management tips, pesticide and fungicide information and proper pruning techniques to have a successful crop. 

If you have further questions after going through that, please continue to reach out. 

Emily