A street in an American community before and after Dutch Elm Disease took its toll.
Dutch Elm Disease (DED) is a fungus disease believed to have been introduced inadvertently into the United States around 1930. The American elm is particularly susceptible to this disease. The fungal growth blocks vessels that carry water from roots to leaves, thus causing the leaves to wither and yellow. As the growth of the pathogen increases, the wilt progresses throughout the crown of the tree, and the tree dies, usually in about a year.
The fungus growth is carried from tree to tree by elm bark beetles. In the fall, adult beetles lay eggs beneath the bark of dead or dying trees, and larvae emerge from the eggs and over-winter in the wood in "brood galleries". In addition to growing in the water-conducting vessels of elms, the fungus growth prospers in the channels of the brood galleries, and the fungus spores, or reproductive structures, contaminate the beetle larvae. In the spring, larvae metamorphose into adult beetles. The adults move away from fungus-infected trees, and inoculate fungus spores into uninfected trees while feeding on the tree bark.
The fungus can also be passed from an infected to a healthy elm if roots of an infected tree contact roots from an uninfected tree and the two root systems fuse. In this case, the previously uninfected tree dies rapidly.
An awareness of the fungus growth characteristics and the fungus-beetle relationship has resulted in the use of methods that attempt to: (1) cure trees that are already infected; and (2) prevent the spread of the disease. If the disease appears to be confined to a limited number of branches, they are pruned from the tree. If the disease has progressed extensively, the tree is removed. Diseased wood is burned in order to prevent the spread of the fungus. There is some disagreement about the use of insecticides, but trained personnel can inject certain fungicides into trees that will spread throughout the tree vascular system. The fungicide injection approach has been most successful when used as a preventative measure.
Although DED has spread incredibly rapidly throughout the United States and Canada, information concerning its control is readily available to the public, and co-operative efforts have helped to keep the effects of the disease to a minimum.
Credit: The "before and after" photograph
showing the effects of DED appears on the Elm Research
Institute website.
PERTINENT LINKS
The information provided above was primarily derived from the following websites, which funish many other interesting facts about Dutch Elm Disease.