The oak tree is attacked by a large number of pests and diseases including: anthracnose, beetles, blight, borers, brown rot, cankers, chlorosis, galls, leaf miners, leaf rollers, leaf scorch, mealy bugs, mildew, red spider, root rot, rust, scale, thrips and wood rot. Perhaps the most notorious disease is oak wilt, which kills within a matter of weeks by plugging the tree's vascular system. The fungus is disseminated through root grafts and by insects.
Sudden oak death is caused by the fungal pathogen Phytophthora ramorum. It kills most species of oaks and other plant hosts may be vulnerable, such as maples, bay laurels and rhododendrons. Once the spores penetrate bark in the trunk, the fungus eats away at the cambium in a matter of months. Upon its sudden appearance around 2000, most devastated are live oaks in California, USA.