As stated above, oak wilt has been confirmed in a tree in western Illinois this year. Assuming the sample is taken properly, it is not too early to sample for this disease.
Symptoms vary depending on the oak species involved.
The leaves curl slightly and turn a dull pale green, bronze, or tan, starting at the margins. Usually by late summer, an infected tree has dropped all its leaves. We have seen red oaks progress from bronze to dead in as little as 3 weeks. The white and bur oak group generally shows symptoms on scattered branches of the crown. Their leaves become light brown or straw colored from the leaf tip toward the base.