Wednesday, January 25, 2012

Stranger Danger - Dutch Elm Disease

As lovely as our American elms are, they are constantly threatened by Dutch elm disease (DED), Ophiostoma novo-ulmi and O. ulmi. This is a fungal infection that spreads from diseased trees to healthy trees through contact, often by beetles carrying the fungus, but also through the root systems and by well-intentioned individuals with their pruning shears. These people, sometimes even trained arborists, can spread the very disease they’re trying to eradicate if some basic steps aren’t taken. 

DED symptoms appear in individual branches, turning the leaves yellow or brown and withered. Meanwhile, the disease is spreading through the vascular system of the tree (the way it gets its water), affecting other branches and eventually taking down the whole tree. That can happen in just one season.

American elms in the District have a 5 percent chance of dying because of DED. There are American elms that are resistant to DED, but those cultivars are susceptible to other threats. The best practice is to identify infected branches early and eliminate the offender before the disease has a chance to spread.

If you want more information on identifying and managing DED in your trees, you can read
this report by the Department of Agriculture’s Forest Service. Also visit our website for information on our American Elm Restoration Program.

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