Thread blight is a fungus disease caused by Corticium stevensii. The disease is primarily a problem in poorly managed orchards in the southeastern United States. Thread blight symptoms are readily noticed in early summer. Leaves wilt and turn brown, usually in the interior or shaded portions of the tree. Dead, curled leaves cling to blighted branches, frequently in mid-branch, with unaffected leaves still appearing on both sides of the diseased area. In well-managed orchards, the disease is usually not seen until after harvest when the fungicide spray program has been discontinued. Positive diagnosis in the field is made by observing signs of the fungus. For more information and images, read this article on Thread Blight.
Answer provided by Alan R. Biggs, West Virginia University.