vascular wilt diseases that appeared in the early 20th century. The other two vascular wilts are chestnut blight (1900–1950) and Dutch elm disease (1928–1980). Each of these diseases have depopulated their respective host tree populations. Chestnut trees were the dominant overstory tree species before chestnut blight and elms were an iconic landscape tree that bordered streets before Dutch elm disease. Oak wilt and the newly emerging emerald ash borer have the potential to devastate other important North American tree species with large geographical and cultural significance. Range expansion of oak wilt to the Western United States (or to other continents) is a major concern. The asexual stage of oak wilt was first described in 1942 in Wisconsin. Soon thereafter the disease was reported throughout the Upper Midwest and Central forests. The early 20th Century coincided with oak regeneration after significant logging in the Mid-Atlantic and Great Lakes region. Deforestation and fire suppression in this region altered the ecology to favor oak–hickory forests, instead of coniferous forests and grasslands. Subsequently, the host for the disease became more prevalent and promoted oak wilt infections. Moving timber during the late 19th Century and early 20th Century, in the period of railroad expansion, coincides with the discovery of the oak wilt disease in the United States. The origin of the disease is unknown, but probably emerged from Mexico, Central America, or South America. Mexico is the global center of oak diversity, supporting it as the endemic range of oak wilt. Any biocontrol or disease resistance for this pathogen will likely come from Mexico. The disease currently affects much of the eastern and central US, from northern New York to Central Texas. It is particularly common in the Midwest where conditions are usually favorable for spore production and beetle activity during spring and early summer. Oak wilt is a major problem in Illinois, Iowa, Michigan, Minnesota, Texas, and Wisconsin. Disease cycle The fungus overwinters on dead tissue from diseased trees. Symptoms first appear in spring and summer. Highly susceptible species typically die within one year (often within six weeks) after symptoms appear. Symptoms begin in the tops of trees and can be difficult to notice. The disease progresses inward and downward from the tree top. Leaves become chlorotic beginning at the leaf tip and leaf edges. An abrupt demarcation of chlorotic veins and green tissue is often a distinguishing characteristic in live oak infections. The