Sam - This sounds like verticillium wilt, although Ginkgo biloba is listed as resistant to the wilt. Take a look at the following Virginia Tech webpage and see if the symptoms sound plausible: Verticillium Wilt of Shade Trees . It's always heartbreaking to lose trees - great sympathy.
Sybil
Sybil Mays
Paradise Nursery Gourmet Fruit Plants
6385 Blackwater Road
Virginia Beach VA 23457
757-421-0201 FAX 757-421-7043
Paradise Nursery - Figs & Fruit Plants