Red oaks:With the red oaks, including Spanish oaks or blackjack oaks, you really do not have a good leaf characteristic to diagnose oak wilt. The literature describes “watersoaking” or “bronzing” of red oak leaves caused by oak wilt, but these characteristics are difficult to identify. The main diagnostic criterion for the Spanish oak is the leaves turning red at the wrong time of the year. This color change occurs very rapidly; all of a sudden the entire tree turns red. A red oak dying of oak wilt holds onto its leaves (it does not drop them like the live oak). This process, from initial infection to death, can happen as quickly as 4 to 6 weeks, or even as quickly as a week in a red oak.
Oak wilt can also be diagnosed by sending a fairly large sapwood sample to a lab where they culture for the fungus in a petri dish. Taking the large sapwood sample is damaging to the tree, and thus this is not a good method to diagnose oak wilt.
Oak wilt is best diagnosed by observing the visual symptoms on the leaves and the pattern of death of the tree.
How does oak wilt spread?