The wilted graying leaves are likely cause by Powdery Mildew, a fungal pathogen, and symptoms include white coating on leaves which may appear gray in color. You can explore our Powdery Mildew Disease on Trees and Shrubs to for more information on conditions that favor the disease and it's management. 

There could also be Botryosphaeria canker (also a casued by a fungus) killing the branches. You can visit the Virginia Cooperative Extension webpage on Botryosphaeria Canker and Dieback of Trees and Shrubs in the Landscape to learn more about they symptoms and managing the disease. Heat and drought stress can increase disease incidence. 

Pruning can help with both problems by creating better air circulation to reduce humidity levels (powdery mildew) and removing the dead/dying branches also removes the fungus in the dead wood which can move to the healthy wood (Botryosphaeria canker).  Please remember to sanitize pruning tools to help prevent the spread of the fungus. You can visit out webpage on Pruning Trees in the Home Landscape for more detailed information on how to prune.

-Julia