Oak decline is a term that describes the deterioration of oak trees, in some cases eventually leading to death of the tree. A slow-acting phenomenon known as chronic oak die-back, thought to be due to an interaction between many different factors (pests, diseases and environmental conditions) has been known since the early part of the twentieth century.
In recent years another problem called acute oak decline has come to the fore. Thought to be caused by a bacterial pathogen, this can lead to a rapid deterioration of affected trees.
Oak decline is unrelated to the disease known as sudden oak death which, despite its name, does not notably affect English oak trees.