There is more than one disease that affects oak trees. Anthracnose is a fungal disease that is usually not fatal to an oak tree. Michigan also is seeing oak wilt which is a serious disease and is best diagnosed by a tree expert. There are some resources that may be helpful to you since I cannot tell from your picture what the disease is. Go to extension.iastate.edu and search sick oak leaves. Also migarden.msu.edu and search anthracnose and/or search oak wilt. Having a certified arborist look at your tree may also be helpful. You can find one in your area by searching treesaregood.com. I hope this helps you.