Oak wilt effects all Oak species, but has different results and signs with each group. Ceratocystis fagacearum is the fungal pathogen that causes Oak Wilt. It is a vascular disease, meaning the fungus is only found in the outermost xylem of the tree. This fungus is thought to be native of the Eastern US but the problems identifying and isolating it delayed the recognition of the true effects of the fungus until the 1980's. Oak wilt is a very aggressive disease, currently it is one of the most serious tree related diseases in the Eastern US-killing thousands of Oaks each year in both forest and landscape settings.
Oaks in the Red Oak family- such as Black, Northern Red, Northern Pin and others with pointed edged leaves are particularly susceptible and when infected usually die over the course of a single season-some declining to the point of complete defoliation in a matter of weeks. Infected Red Oaks will begin wilting from the top of the tree down, the leaves will gradually become bronze in color and fall off of the tree.
The Live Oak however is not so predictable, it's infection level and timeline is effected by many other variables in the environment. Usually however, Live Oaks infected will die within a six month period from the first sign of decline. Lives Oaks foliar symptoms differ from those of the Red and White Oak. An infected Live Oaks leaves will develop chlorotic veins that eventually turn necrotic prior to falling from the tree.
Oak Wilt fungus spreads in two basic ways. Spores can be transferred from an infected tree to a healthy tree by insect movement or The fungus can move from the roots of an infected tree to those of a healthy tree through root grafts.
Oak Wilt is very similar to Dutch Elm disease but considered to be more controllable. On good factor to consider is the nitidulid Beetles that carry the Oak Wilt Fungus do not have chewing mouth parts, so in turn would need another creature or a damaged portion of the tree to make the transfer. This is different from the Beetles that carried Dutch Elm disease, they do have chewing mouth parts and are able to enter any tree without help.
When an Oak has died from Oak Wilt, trees should be chipped and then burned or covered with plastic sheeting to speed composting. The heat from the chips composting should destroy or severely enervate the fungus. Logs from infected trees should never be moved to unaffected areas, even for use as firewood.
More at www.ArundelTreeService.com or www.MeetATree.com
Downloadable Oak Wilt fact sheets:
Joseph O'Brien, USDA Forest Service, bugwood.org (Photos# 1,3,4,6 & 7)
Forestthreats.org with Google Earth overlay (Photo #2)
Wikipedia (Photo #5)