How Do Trees Catch Dutch Elm Disease?

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    Geography

    • Dutch elm disease spread throughout Europe in the 1930s. By 1930, it had found its way to Ohio and in 1933 it was found in New York. States in the Midwest had their first reported Dutch elm case in 1961. In a mere 30 years, this crippling fungal disease had spread throughout all of Europe, Asia and the United States.

    Beetles

    • Two beetles are the primary cause of Dutch elm disease: native elm beetle and European bark beetle. Much like the disease, the European bark beetle was introduced to the United States by Europe. as the name implies. The beetles feed on diseased trees and spread to healthy trees, thus infecting them with the fungus. In addition, these beetles pick dying, damaged or dead elm trees as their preferred breeding grounds. Once the beetles emerge in the late spring, they spread out to find more breeding .

    Root Grafts

    • According to Oklahoma State University, the disease commonly spreads through root grafts. Root grafts occur when two trees are planted close to each other and their root systems fuse together. The disease will spread from one elm to a healthy elm through the fusing root grafts. This is one of the reasons that it is important to remove any diseased elm trees from the yard and away from healthy trees.

    Sanitation

    • Dead, diseased elm trees in the yard will result in more unhealthy trees. Because the beetle population is attracted to dead trees, they will breed and spread Dutch elm to healthier plants. Oklahoma State University says a branch the size of a fireplace log can breed up to 1,800 beetles. If that branch is infected with the fungus, almost all 1,800 beetles can go on to infect other elms with the fungus.

    Insecticide/Fungicide

    • Leaving elm trees to their own devices will not only result in their death, but also cause more unhealthy trees. An application of insecticide in the late fall makes controlling the beetles easier. Fungicide injections can be used on trees that are less than 5 percent infected with the disease. Gardeners must examine their elm trees to find out if the tree has been infected with Dutch elm and its rate of survival.

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