A: Oak wilt is caused by the fungus Ceratocystis fagacearum. Oak decline is a stress-induced problem. There are several diseases that cause decline. For example, you have oak trees and you build a parking lot around them. Over the course of the next 20 to 25 years, the trees slowly begin to die. The trees across the street in an open lot are healthy; the decline disease never affects those trees. The paving of the parking lot and the soil compaction were the initial stress factors. Over the course of time, these factors are slowly killing the trees. Eventually, it reaches the point where even removal of the parking lot cannot save the trees because they are too far gone. This is the textbook definition of “oak decline”.
Here in Central Texas, folks use the terms “oak wilt”, “oak decline” and “oak blight” essentially interchangeably.
Drought is also a stress causing oak decline.